ct review
_________ __________ and _________ studies were the first exams to be routinely acquired with a helical technique.
Chest, abdomen and pelvis
How does varying the collimation affect the dose for that slice?
Collimation determines the radiation penumbra and it also affects scatter radiation.
Computed Tomography, or CT, has been commonly called_______________ or_________________ in the past.
Computerized Axial Tomography, CAT-Scan
If standard filtered back projection is applied to a cone beam, this results in an artifact known as a/an _____________________.
Cone Beam Artifact
What is being used in the oncology department in order to verify patient positioning prior to receiving radiation therapy?
Cone Beam CT
On single row detector scanners, what determines the final slice thickness?
The collimation
Where does the analog signal go to after it leaves the Sample-and-Hold Component?
To be digitized by the Analog-to-Digital Converter or ADC.
What is the purpose of a reconstruction filter, or kernel?
To enhance the important characteristics of the image before back projection is performed
T/F: Fear and stress resulting from the CT examination have also been known to trigger a histamine release.
True
T/F: Filtered back projection alone fails to produce acceptable images when the x-ray beam collimation is greater than 20 mm.
True
Window adjustments allow us to concentrate on either ______ _________ detail or ______ _________ contrast by varying _____________ and ____________ settings.
high resolution, soft tissue, brightness and contrast
In order to keep the concentration of the contrast media in the vessels sufficiently dense, ________ rates of injection of approximately ___ to ___ ml/sec are used in CTA studies.
higher, 3 to 5 ml/sec
IV contrast agents are said to be _______________ or ______________ compared to blood plasma.
hyperosmolar or hypertonic
_________________ (hypertonic / hypotonic) solutions will cause a net movement of water from within the tissues into the vascular space.
hypertonic
Volume rendering can incorporate information from the entire _______ _______ set. rather than just a/an ________, into the post-processed images, enabling visualization of structures _________ ____ _________ ____ _________.
image data, surface, above and below the surface
CT scanners have many user-selectable parameters which can dramatically affect clinical _________ __________, __________ _______ and ______.
image quality, patient dose and throughput
The grid of pixels comprises the _______ ________.
image, matrix
Barium sulfate is an _______, ___________ substance that is not __________ or ___________ in the body.
inert, insoluble, absorbed or metabolized
The slice thickness must be chosen carefully to maintain an acceptable _______ _________ and appropriate _____________ while minimizing __________ __________.
noise level, coverage, partial voluming
When a ____________ agent is injected, the entire molecule remains intact as it passes through the body and is excreted in the same form by the kidneys.
non-ionic
Due to __________, the patient's blood vessels will dilate to compensate for the increased volume of fluid in the vessels during an IV contrast injection. This type of reaction mechanism would be referred to as what?
osmosis, Chemotoxic Reaction Mechanism.
If the reconstruction interval is less than the slice thickness, the reconstructed slices will _____________.
overlap
Using ____________ ________ in the initial data set improves the quality of the reconstructed images.
overlapped
In regards to an MIP image, in a vascular dissection in which the true and false lumens are enhanced to the same degree, the membranes will only be visualized where they are oriented directly ________ to the viewing direction.
parallel
The edge gradient effect is one of the many causes of _________ artifacts in CT images.
streak
The pitch determines how _________ the x-ray path is during a helical scan.
stretched
Intrathecal contrast agents are injected into the spinal ________________ space during a ______________ exam of the spine.
subarachnoid, myelographic
The ARRT Code of Ethics offers __________ for ethical conduct.
suggestions
On conventional or serial scans, the ________________ determines if the slices will be contiguous or if there will be a ______ or __________.
table increment, gap or overlap
If more than one tissue is contained in a voxel, the CT number is determined by a _____________ of the densities of the contents of the voxel.
weighted average
Describe the Patient Coordinate System.
x-axis: The axis extending from the patients left to right side. (left to right)\ny-axis: The axis extending from anterior to posterior through the patient. (anterior to posterior)\nz-axis: The axis extending along the patient table and the long axis of the patients body. (head to feet)
What does MDCT stand for?
Multi Detector Computed Tomography
What does 3D SSD stand for?
Three Dimensional Shaded Surface Display
What does nutate mean?
To angle
What artifact can occur when more than one tissue type is contained in a voxel?
Partial volume averaging
What are two examples of Graphic Input Devices?
1.) A Mouse\n2.) A Trackball
What are the advantages of having a duel modality PET/CT scanner?
1.) Acquiring the PET/CT images back to back w/out any patient motion makes it easier to register the PET and CT images accurately.\n\n2.) Information from the CT scan simplifies a necessary step performed on the PET study known as Attenuation Correction.
What are the three possible paths that a fast moving electron may take as it passes through an atom?
1.) Directly collide with nucleus. (unlikely) (Bremsstrahlung)\n2.) Enter the vicinity of the nucleus and loose energy, slowing down, changing direction and emitting Bremsstrahlung radiation.\n3.) Collide with an electron in an inner shell of the target atom. (Characteristic)
What are the three things that are transferred by the slip ring?
1.) Electrical Power\n2.) Scanning Instructions\n3.) Detected Signals
What are the three conditions required for the detectors used in a CT system to measure an incoming photon?
1.) Enter the detector - be "Captured"\n2.) Collide with a detector - be absorbed\n3.) Produce a measurable result
List the four key aspects of a 3rd generation CT system.
1.) Fan Beam\n2.) Multiple detectors along and arc\n3.) The tube/detector assembly rotates around the patient ( without translating)\n4.) Total scan time faster than 1 second per image
List the four key aspects of 4th generation CT systems.
1.) Fan Beam\n2.) Multiple detectors encircle the patient and do not rotate around the patient.\n3.) Only the tube rotates around the patient\n4.) Total scan time of 1 second per image or faster.
List the benefits of MDCT.
1.) Faster Scans\n2.) Increased anatomical coverage\n3.) The ability to use thinner slices to improve resolution along the slice direction
List six advantages of helical scanning.
1.) Faster Studies\n2.) More coverage in a breath-hold\n3.) No missed anatomy\n4.) Less contrast agent needed\n5.) Arbitrary slice positioning\n6.) Ideal dada for post-processing
In what two types of scans does the table move continuously while scanning?
1.) Helical Scans\n2.) Localizer Image (Scout)
What are the only two ways to cover anatomy faster in a helical study with a single row detector scanner?
1.) Increase the slice thickness\n2.) Vary the pitch
List three Scanning Methods
1.) Localizer\n2.) Conventional, or serial, CT\n3.) Helical CT
What are other names for MDCT?
1.) Multi-Slice Scanners\n2.) MSCT\n3.) Multi-Array Scanners
What types of information/commands can be initiated from the operators console?
1.) Patient Information\n2.) Imaging Parameters\n3.) Post Processing Commands\n4.) Image Manipulation
What are the two types of collimators that exist in CT scanners?
1.) Pre-Patient\n2.) Post-Patient
What is the purpose of collimation?
1.) Reduce the dose to the patient\n2.) Reduce the production of scatter radiation
Give three examples of where Conventional CT is the preferred scanning method of choice and explain why.
1.) Some neurological exams such as studies involving the temporal bones; because it demands fine detail\n2.) Cases involving obese patients\n3.) Cardiac calcium scoring studies; because it mimics the results that would be obtained from EBCT
In MDCT scanners, what are the two basic types of detector arrays?
1.) Symmetric\n2.) Asymmetric
What are the two functions of post-patient collimators?
1.) To provide better definition to the slice thickness on single-row detector scanners.\n2.) To reduce the amount of scatter radiation that would otherwise enter the detector system.
How is Bremsstrahlung radiation produced?
1.) When an incoming electron collides with the nucleus of an atom and loses much of it's energy and x-ray photon is produced. (Very unlikely)\n2.) When an incoming electron enters the vicinity of the nucleus of an atom and looses energy, slowing down and producing a Bremsstrahlung photon.
What would be a typical pediatric dose of IV contrast media for a helical scan?
1.5 ml per kilogram of body weight
What is the required difference in density in order for tissues to be differentiated with conventional radiography?
10%
What percentage of the x-ray beam emitted from a CT x-ray tube is Characteristic Radiation
10%-12%
Any measurements above _______ units generally indicates the presence of calcification.
100
What is the typical dosage of IV contrast, injection rate and delay time for studies of the pelvis?
100 ml @ 2 to 3 ml/sec, with a delay time of a few minutes to allow for ureter and bladder enhancement.
What is the typical dosage of IV contrast, injection rate and delay time for studies of the chest?
100 ml @ 3 ml/sec, with a delay time of approximately 20 to 25 seconds
Most scanners today are based on ____________ technology.
3rd Generation
What type of architecture do MDCT scanners have?
3rd Generation
Most Ct Scanners made today still apply similar technologies as those incorporated in which generation of CT Systems?
3rd Generation Systems
How many Generations of CT Systems are there?
4
What injection rate would you use for a CTA?
4 to 5 cc/sec.
After a "projection" of data is obtained in a 2nd Generation System, the tube/detector rotates typically ___________ covering an arc of __________ around the patient.
5 degrees or more, 180 degrees
What was the shortest possible scan time per image with a 1st Generation system?
5 minutes per image
What is the normal/ acceptable range for BUN values?
5 to 25 mg/dl
How long does one "rotation" take on an EBCT scanner?
50 to 100 milliseconds
What is the most commonly used matrix size and is this value typically varied?
512 x 512; No, it is not typically varied.
Approximately what range does Congealed blood fall into?
56 to 76 HU
What is the normal range for creatinine?
6 to 1.7 mg/dl
When does the portal venous phase of liver enhancement occur?
60 to 90 seconds after the start of the injection.
What is the atomic number of tungsten?
74
If a single row detector scanner has 750 detectors in its detector array, how many attenuation measurements would be gathered from one projection?
750 attenuation measurements
The liver receives about _____% of its blood from the portal vein and about _____% from the hepatic artery.
80%, 20%
If a 64 slice MDCT scanner has 850 detector elements in a single array and there are 1700 projections collected per full rotation, how many total attenuation measurements are collected per rotation?
92,480,000 measurements/samples
Define "Digital Image".
A "Digital Image" is a numerical representation of an object that can be recognized and processed by a computer.
First generation CT Systems generated a thin, focused x-ray beam called what?
A "Pencil Beam"
What is 3D SSD?
Reconstructed images of the surfaces of anatomical structures
What things are affected by slice thickness?
1. Anatomical Coverage\n2. Image Noise\n3. Resolution along the direction perpendicular to the acquired images\n4. Patient Dose
What four things does pitch affect?
1. Anatomical Coverage\n2. Scan time\n3. Resolution\n4. Dose
List four techniques for distending the veins.
1. Apply tourniquet\n2. Have patient pump hand\n3. Slap vein\n4. Apply heat
What are the two steps to filtered back projection?
1. Applying a filter to the raw data\n2. Back projection
The amount of attenuation is dependent upon What four factors?
1. Atomic number\n2. Density of electrons\n3. Thickness\n4. Photon energy
What are the two methods used to determine the proper timing between the administration of contrast and the initiation of the CT scan?
1. Automated Software\n2. Test Bolus
What are the two categories of Oral Contrast Media?
1. Barium Sulfate\n2. Iodinated
What are the three phases of tissue enhancement?
1. Bolus Phase\n2. Non-equilibrium Phase\n3. Equilibrium Phase
What are the two ways that x-rays which penetrate the tissues can cause damage to the body?
1. By breaking electron bonds and forming ion pairs (Indirect Effect) (more likely)\n2. By directly disrupting the DNA bonds within the nuclei of cells in the patient's body (Direct Effect)(less likely)
What are the two most frequently used standards for daily quality assurance assessment
1. CT Number Calibration Test\n2. CT Number Standard Deviation Test
What are the four influences on parameter selection?
1. Contrast Resolution\n2. Spatial Resolution\n3. Image Noise\n4. Patient Dose
List the three image quality factors.
1. Contrast\n2. Resolution\n3. Noise
How might beam hardening manifest itself in the resultant image?
1. Cupping\n2. Broad streaks\n3. Regions of decreased density
By asking extensive questions about the patient's medical history there are actually two pieces of information we are trying to learn. What are they?
1. Does the patient have any conditions or tendencies to be intolerant to a contrast agent?\n2. Does the patient have any history of prior surgeries or treatments we would expect to cause the CT images of this patient to differ from normal anatomy?
What must be demonstrated in a lawsuit in order to prove negligence?
1. Duty\n2. Breach of Duty\n3. Injury\n4. Cause of Injury
What are the two factors that determine slice thickness on a single-row detector scanner?
1. Focal Spot Size\n2. Pre-Patient Collimation
List four reasons to increase the pitch.
1. Greater anatomical coverage in less time\n2. Faster scan for trauma\n3. For appropriate contrast timing during a CTA study\n4. Decrease the dose to the patient
Give three examples of bloodborne pathogens.
1. Hepatitis B \n2. Hepatitis C\n3. HIV
What are some steps to reduce the edge gradient effect?
1. If the structure causing the artifact can be identified, it should be moved or the patient should be repositioned if possible\n2. If the scanner allows for an increase in data sampling, or over-sampling, in which a scan arc greater than 360°, is employed, the additional samples will decrease the streak artifact\n3. Use thinner slices
What are two reasons that we might use a reduced pitch?
1. Improving the resolution along the slice direction\n2. Minimizing the appearance of noise in the image.
What are the four groups of contrast media?
1. Intravenous (IV) Contrast Agents\n2. Oral Contrast Agents\n3. Intrathecal Contrast Agents\n4. Intra-Articular Contrast Agents
What are two scanner determined factors that must be considered when calculating delay times?
1. Is it going to be a serial scan or a helical scan? Serial scans take longer so scanning usually starts immediately after injection.\n2. Is it a single-row detector scanner or a MDCT scanner? A MDCT scanner will cover the anatomy much faster than a single-row detector scanner.
How may partial voluming averaging manifest itself in the final CT image?
1. It can appear as blurriness at the margins of an object, where the surface of the object curves out of the slice plane\n2. It can falsely give the impression of pathology in which vague opacities are the result of a slice through the top or bottom of a rounded structure, such as the top of the aortic arch or the diaphragm
What are the two functions of the special transformer oil that surrounds the x-ray tube?
1. It electrically isolates the high voltage anode, filament and cathode connections\n2. It serves to transfer the huge quantities of heat normally generated within the tube to a heat exchanger in the gantry
What are the two categories of lab tests that are required in some facilities before patients can receive IV contrast?
1. Laboratory tests done to determine the kidneys' ability to clear impurities from the vascular system\n2. Tests done to asses the bloods ability to coagulate
Based on osmolality, contrast media can be divided into what two groups?
1. Low Osmolar Contrast Media (LOCM)\n2. High Osmolar Contrast Media (HOCM)
2nd Generation Systems are referred to as having ________ Geometry.
"Fan Beam"
What are the two categories of reaction mechanisms?
Chemotoxic and Idiosyncratic
Where are the instructional commands entered by the technologist?
The CT System Control
What is the CT Number / Hounsfield Unit for air?
-1000
What are the acceptable limits for the CT Number Calibration Test?
-3 to +3
Why was the curved detector array contained in 3rd Generation Systems an improvement over 1st and 2nd generation designs?
-It improved the reproducibility of the "projection data measured across the array.\n-It also minimized certain artifacts that were common in 2nd Generation Systems.
The xenon detector is most sensitive to x-rays coming from which direction and why?
-To x-rays entering the detector straight on.\n-Because the detector has the shape of a narrow, tall chamber
What pixel level (color) is assigned to any CT numbers below the range specified by the window width?
0 (black)
If a detector has an offset difference of as little as _______% with neighboring detectors, a ring artifact may result on the images.
0.1%
Typically, tissues with differences in density of less than ______% can be differentiated with CT.
0.5%
How much radiation is in 1 rad?
1 rad = 0.01 joules of energy per kilogram of matter (the patients weight)
Barium sulfate solutions used in CT are much more dilute than those used in conventional radiography, typically containing a _____ to ______% barium sulfate suspension.
1 to 3%
List four key aspects of 2nd Generation Systems.
1) Fan Beam\n2) Multiple detectors in a straight line\n3) Tube/Detector moved across the patient then rotated by approx. 5 degrees\n4)Total scan time of about 20 seconds per image
What were the 2 most important features of 2nd Generation Scanners which quickly made 1st Generation Systems obsolete?
1) Fan beam geometry\n2) The detector Array
List five types of information/ instructions that are entered at the CT System Console.
1) Patient Information\n2) Imaging Parameters\n3) Post-Processing Technique\n4) Filming\n5) Archiving
List four key aspects of 1st Generation CT Scanners?
1) Pencil Beam\n2) Single Detectors\n3) The tube/detector assembly translated, rotated 1 degree and repeated\n4) Scan Time was 5 minutes per image
If there are 750 detectors in the detector array and 1500 projection are collected per rotation, how many attenuation measurements would be collected for one image?
1,125,000 attenuation measurements would be collected
X-ray photons are attenuated via what two processes?
1. Absorption\n2. Scattering
What are the two slice thickness parameters that must be specified on a MDCT scanner?
1. Acquired Slice Thickness\n2. Reconstructed Slice Thickness or Effective Slice Thickness
List six "moderate" reactions to IV contrast agents.
1. Moderate hives\n2. Change in pulse rate\n3. Hypotension or hypertension\n4. Wheezing\n5. Bronchospasm or laryngospasm\n6. Facial edema
What are the two types of printers used to print CT images?
1. Multi-Format Camera\n2. Laser Camera
List eleven "minor" reactions to IV contrast agents.
1. Nausea\n2. Chills\n3. Vomiting\n4. Feeling of warmth\n5. Minor hives\n6. Unusual, metallic taste sensation\n7. Itching\n8. Shaking\n9. Headache\n10. Dizziness\n11. Sweating
What are 4 applications for 3D SSD/
1. Orthopedics\n2. Planning for craniofacial surgery\n3. Planning for neurosurgery\n4. Planning for radiation therapy
What questions should be asked during screening for contrast agents?
1. Previous reaction to contrast?\n2. Allergies to iodine or barium?\n3. Conditions such as hypertension, heart disease, asthma, sickle cell anemia, renal impairment or diabetes?
What are the three tests that determine the bloods ability to coagulate?
1. Prothrombin Time (PT)\n2. Partial Thromboplastin Time (PTT)\n3. Platelet Count
What are the two types of FOVs?
1. Scan Field Of View (SFOV)\n2. Reconstruction or Display Field Of View (RFOV or DFOV)
List 12 CT studies of the head that do not require the administration of IV contrast media.
1. Sinusitis\n2. Trauma\n3. Grave's disease\n4. Early-stage cerebrovascular events\n5. Early-stage subdural hematoma\n6. Hydrocephalus\n7. Dementia\n8. Mastoiditis\n9. Labyrinthitis\n10. Facial or seventh nerve palsy\n11. hearing loss\n12. Studies of the petrous and temporal bones
What defines the two dimensions of a voxel?
1. Slice thickness\n2. In-Plane Spatial Resolution
What are the two types of lab results important to CT?
1. Tests to determine renal function\n2. Tests to determine the bloods ability to coagulate
List 4 key screening issues.
1. The reason for the exam\n2. The potential for pregnancy\n3. The patient's medical history\n4. The values of lab tests
What are the 7 sets of patient rights?
1. The right to Information\n2. The right to Choose\n3. Access to Emergency Services\n4. Being a Full Partner in Health Care Decisions\n5. Care Without Discrimination\n6. The Right to Privacy\n7. The Right to Speedy Complaint Resolution
What are the three goals of the Patients Bill of Rights and Responsibilities?
1. To strengthen consumer confidence that the health care system is fair and responsive to consumer needs\n2. To reaffirm the importance of a strong relationship between patients and their health care providers\n3. To reaffirm the critical role consumers play in safeguarding their own health
What are some techniques to minimize the effects of beam hardening?
1. Use a beam hardening correction algorithm\n2. Use thinner slices\n3. Use diluted contrast agents.
What are three general categories of CT artifacts?
1. User related artifacts\n2. System related artifacts\n3. Patient motion artifacts
What are the four hardware factors affecting dose?
1. X-ray tube to patient distance\n2. Filtration\n3. Pre-patient Collimation\n4. Multi-row detector design along with dose minimizing software
What is today's defination of a "scan"?
The collection of anatomical information during the time the xray beam is on.
What is the typical dosage of IV contrast, injection rate and delay time for studies of the neck?
100 to 125 ml @ 2 to 2.5 ml/sec, with a delay time of approximately 35 seconds
What is the typical dosage of IV contrast, injection rate and delay time for studies of the abdomen?
100 to 150 ml @ 2 to 3 ml/sec, with a delay time of approximately 65 to 75 seconds for the liver, 50 to 60 seconds for the pancreas, and 75 to 85 seconds for the kidneys and adrenal glands
What is a typical dose of IV contrast for a head scan?
100ml
Approximately where does blood fall on the CT Number / Hounsfield scale?
12 HU
Manufacturers claim that their dose-optimizing software which automatically varies the mA allows for dose reductions ranging from ______ % to ______%.
15% to 55%.
How many individual projections might be obtained during one full rotation (360˚)?
1500
What size catheter is generally used for IV contrast injection?
18-22 Gauge
How many different projection were need in a 1st generation system in order to construct and image?
180\n(180 degree arc)
When was the 1st CT System commercially introduced for general clinic use?
1973
When were 3rd Generation Systems first introduced?
1975
What would be a typical pediatric dose of IV contrast media for a conventional, serial scan?
2 ml per kilogram of body weight
What is the average annual radiation dose equivalent from radon?
2 rem
What is the routine IV contrast injection rate?
2 to 3 cc/sec.
How much should the needle tip be withdrawn before advancing the catheter up the vein?
2 to 3 millimeters
When does the hepatic arterial phase of liver enhancement occur?
20 to 40 seconds after the start of the injection.
What pixel level (color) is assigned to any CT numbers above the range specified by the window width?
255 (white)
How many shades of grey can an operators console display?
256
In a 1st generation scanner, what did you call the series of measurments the was collected as the tube/ detector assembly translated across the patient?
A "Projection"
What is another name for a CT artifact?
A CT anomaly
Define a Chemotoxic reaction.
A Chemotoxic reaction mechanism is one that can be directly attributed to factors that include: physiological properties, the total volume of agent injected and the rate of injection.
The spreading of the x-ray photons along the z-direction is responsible for an artifact called what?
A Cone Beam Artifact
What do we call each small region of a digital image's grid/
A Picture element or Pixel
What do we call a single picture element of the image matrix?
A Pixel
If a patient is sedated, what type of monitoring device is recommended?
A Pulse Oximeter
Which type of detector is the most sensitive to x-rays coming in from various angles?
A Solid State Detector
What do we call a volume element?
A Voxel
What motion artifact appears as a double margin of a tissue boundary?
A ghost artifact
In the days before continuous rotation scanners, what transferred the high voltage from the generator to the x-ray tube?
A large, bulky, high tension cable
In a spatial resolution test for CT, what is one hole and one space referred to as?
A line pair
What is the extra step involved in helical image reconstruction?
A mathematical calculation has to be ran on the helical raw data in order to divide it into individual, planar data slices that can then be reconstructed into images using the same mathematical process applied to conventional image data sets.
What type of printer requires a photographic focusing lens?
A multi-format camera printer
What type of contrast is administered for a virtual colonoscopy study and how is it administered?
A negative contrast agent such as air or CO2 is administered through the rectum in order to distend the bowel so that we can see the interior surfaces.
Define an "Integer".
A positive (+) or negative (-) whole number
Explain the word "Projection".
A projection can be taught of as a "view" of the anatomical cross-section from a particular vantage point.
What do we call the filter that is applied to the raw data during image reconstruction?
A reconstruction filter or kernel
As a general rule, what reconstruction interval will produce excellent MPRs, MIPs, or other three-dimensional renderings?
A reconstruction interval equal to 1/3 to ½ of the slice thickness
Which artifact results from a faulty or miscalibrated detector element?
A ring artifact
What is the 1st Generation defination of a Projection?
A series of measurments collected as the tube translates across the patient.
What is a solid state detector made of?
A solid crystalline substance which is much more dense than Xenon.
What is a 'Test Bolus"?
A test bolus is used to determine how long it takes for a bolus of IV contrast media to reach the region of interest.
How much faster could a 2nd Generation Scanner collect the required data compared to a 1st Generation Scanner?
About 10 times faster
How many shades of grey can the human eye distinguish?
About 20 shades of grey
About how many detectors comprised the detector array in 2nd Generation Systems?
About 30
About how long would you wait before scanning the head after the injection of IV contrast for studies involving metastatic disease, AIDS or multiple sclerosis?
About 45 minutes
About what percentage of patients injected with IV contrast will have some sort of reaction?
About 6% to 8%
The______________________ indicates which rows of detectors are being used to measure the photons that pass completely threw the patients body.
Acquired Slice Thickness
How is the acquired slice thickness calculated on an MDCT Scanner/
Acquired slice thickness = The thickness of the x-ray beam # of slices acquired per rotation
What are the key vital signs and their normal values?\nPulse:
Adult 70 to 100 BPM\nAthletic 45 to 60 BPM\nChild 95 to 110 BPM\nInfant 100 to 180 BPM
List two types of negative contrast agents.
Air and water
Other than barium and gastrographin, what are some other oral contrast agents?
Air and water
What do we call the precautions associated with airborne infection transmission?
Airborne Precautions
What form of infection transmission occurs by dissemination of either airborne droplet nuclei (small-particle residue [5 um or smaller in size] of evaporated droplets that may remain suspended in the air for long periods of time) or dust particles containing the infectious agent?
Airborne Transmission
What should you do if your patient is having a seizure?
All restraints and objects that could cause harm should be removed and the patient should be eased into a resting position (e.g., on the patient table, a chair, or the floor).
How does EBCT work?
An electron gun produces an electron bean which is electro-magnetically directed toward an array of tungsten anodes located around the patient. X-Rays are then generated from the collision of electrons and the tungsten anode.
Define an Idiosyncratic reaction.
An idiosyncratic reaction is one that is caused by anything besides the type, amount or rate of contrast injected.
What does the digitizing process involve?
An integer is assigned to each amplified electrical signal. The value of the integer is determined by the signal's strength. The stronger the electrical signal, the larger the integer. Each integer also corresponds to a shade of gray in the image. This allows the display hardware to assign a specific gray level to the region of a CT image from which this attenuation information was detected.
What type of shock occurs from IV contrast injection?
Anaphylactic shock (sudden massive vasodilation)
The patient table is fed threw the ___________ of the gantry.
Aperture
What is the CT Number / Hounsfield Unit for fat?
Approximately -80
How big is the opening in each xenon gas detector?
Approximately 1mm
What is the CT Number / Hounsfield Unit range for soft tissue?
Approximately 30 to 80
How much can a gantry tilt/angle?
Approximately 30˚ from the vertical plane
What is the melting point of tungsten?
Approximately 3400˚ C
How warm should IV contrast be before being injected into the patient?
Approximately body temperature
How much of the Iodinated oral contrast is absorbed by the body?
Around 0.1 to .5%
What is the concentration of particles in an ionic, high osmolar IV contrast agent?
Around 1300 to 1600 mOsm/kg
What is the concentration of particles in a non-ionic, low osmolar IV contrast agent?
Around 500 to 850 mOsm/kg
Why was dose-optimized software developed?
As a response to the realization that the newer scanners (MDCT) would otherwise increase the dose to the patient.
Why were 4th generation systems developed?
As an alternative technology to 3rd generation systems
What was the scan time for a single image in a 2nd Generation Scanner?
As little as 20 seconds
Describe the mechanism for arcing within the tube.
As the tube ages tungsten gas accumulates inside of the tube. the tungsten gas acts as an alternate pathway from cathode to anode and is the cause of arcing within the tube
How will arcing within the tube manifest itself during the later stages of tungsten gas formation?
As the tungsten gas increases in density the frequency and severity of the arcs will increase and result in more severe noise or more numerous streaks
How thick should the slices in a CTA study be?
As thin as possible
Why is iodinated oral contrast contraindicated if there is a risk of aspiration/
Aspiration of these agents can result in severe pulmonary edema
At about what thickness does an x-ray beam cease to be referred to as a fan beam and start being referred to as a cone beam?
At about 20mm
Define Attenuation.
Attenuation is the progressive reduction of the intensity of the x-ray beam as it passes through the patient's tissues.
What do we call the attenuation information collected at each projection?
Attenuation profiles
What are the two tests that determine renal function?
BUN and Creatinine
Define "Back Projection".
Back Projection is a technique which adds together the attenuation information collected from all of the projections.
When an x-ray beam enters tissue and looses lower energy photons to attenuation, there is am increase in the mean energy of the beam. This is referred to as what?
Beam Hardening
Restricting the lower energy photons from entering the patient minimized an undesirable effect called _________ ________ as well as the _________ _________.
Beam Hardening, Patient Dose
What artifact might be cause by scanning the patients chest or abdomen with their arms at their side?
Beam hardening
Define Beam Hardening
Beam hardening is the increase in average energy of the x-ray beam as it penetrates tissue
Why must care be taken in choosing the scan FOV?
Because correction and calibration algorithms are often affected when selecting a scan FOV. For example: Choosing a head scan FOV of 25 cm is not equivalent to choosing a small body scan FOV of 25 cm, and will not produce identical image quality.
Why was slip ring technology such an improvement over existing technology?
Because it eliminated the winding up of the high tension cable and allowed for faster exam times due to the eliminated need for reversal of the gantry frame rotation between scans
Why is the liver a unique organ?
Because it is the only organ with a dual blood supply
Why is it not recommended to continue scanning after tube arching outside the tube in the surrounding oil?
Because it is very destructive to the tube and high voltage generator and because it is not possible to predict the effects from continued arcing on the oil pressure within the tube housing and the oil cooling circuit
Why is there such great value in PET/CT scans?
Because it shows the exact location of metabolism changes (tumors/growth) based off the high resolution CT images that are registered to the PET images.
Why is the cephalic vein less desirable for insertion of the catheter/
Because it's tortuous route makes the flow more likely to be impeded when the patient's arms are raised.
Why do CT localizer images have better soft tissue contrast than conventional films?
Because of the reduction in scatter radiation as a result of pre-patient and post-patient collimation.
Why are oral iodinated contrast agents tolerated so much better than IV iodinated contrast agents?
Because oral agents use a much lower concentration of iodine
Why might it be important to ask the patient if they have had had radiation therapy?
Because scarring caused by radiation therapy mimics lung disease.
Why is it called Characteristic Radiation?
Because the energy level of the emitted photons is a characteristic of the specific target atom.
Why is it important for the patient to be well hydrated both before and after the administration of IV contrast?
Because the hypertonic nature of the IV contrast agent can cause a net movement of water from within the tissues into the vascular space(dehydration).
Why is spatial resolution and noise not affected by magnification?
Because the same amount of anatomy is represented by each pixel.
The term "scan" slightly changed meaning with the introduction of 3rd Generation Systems. Why?
Because the tube/detector array no longer had to "translate" across the patient.
Why are IV contrast agents used in studies of the neck?
Because they allow for the differentiation of blood vessels from lymph nodes and outline the epidural venous plexus
Why are barium sulfate agents usually well tolerated by the body?
Because they are not absorbed
Why can't xenon detectors be used in fourth generation systems?
Because they aren't sensitive to x-rays entering the chamber from any other direction than strait-on.
Why streaks from the edge gradient effect less apparent on today's scanners?
Because today's scanners utilize high data sampling rates and small detector apertures
Why is vascular depiction most accurate with a narrow VOI?
Because using a narrow VOI reduces the inclusion of extraneous high intensity background pixels and increases the conspicuity of vascular structures.
What do we call the exam frequently performed to differentiate liver lesions with arterial blood supplies from those with venous blood supplies?
Bi-phasic study of the liver
What is another name for Bremsstrahlung Radiation?
Breaking Radiation
How can the severity of the osmotic effect, and the associated reaction, be reduced?
By administering non-ionic, low osmolar contrast media.
How is the actual dose from multiple adjacent slices measured?
By an important indicator of radiation dose called the CT dose index, or CTDI.
In regards to MIP images, the lack of 3D information can be partially offset by doing what?
By generating multiple MIP images at different angles about an axis of rotation and then displaying them as a movie, or cine loop.
How does the 3D SSD reconstruction program begin?
By stacking the transverse slices to form a volume of anatomical data.
How do we optimize in in-plane spatial resolution?
By using a small reconstruction FOV
How can the viscosity of any contrast agent be reduced?
By warming the agent to approximately body temperature.
What are the two most common modalities to fuse?
CT and PET
MIP is most typically used for ____________________ (as well as _____________ studies).
CT angiography, MR angiography
Beam hardening is responsible for variations in the ____________ of a given tissue type from the ____________ to the ________ of and image.
CT number, periphery to the center
The pixels in a image represent the _____________ of a volume of tissue called a __________.
CT number, voxel
The ________ assumes that consecutive slices are contiguous.
CTDI
Delay times will vary from patient to patient depending on what/
Cardiac output
If your scanner is going to be collecting more than four slices per rotation (greater than 20mm) what type of reconstruction method will be used?
Cone Beam Reconstruction
Describe Cone Beam Artifacts.
Cone beam artifacts are associated with multi-row detector scanners that use only simple filtered back projection reconstruction. These artifacts cause peripherally located structures in the image to have a spoke or star-like appearance.
Which type of precautions are designed to reduce the risk of transmission of epidemiologically important microorganisms by direct contact?
Contact Precautions
What do we call slices with no gaps between them?
Contiguous
What is another name for analog waveform
Continuous waveform
Define Contrast Resolution.
Contrast Resolution is the ability to differentiate small differences in density on the image.
What scanning method is the "Gold Standard" for CT image Quality?
Conventional or Serial Scanning.
Which scanning method entails the x-ray tube rotating around the patient while the patient table remains stationary?
Conventional, or serial, CT
What is the process of applying a filter to the raw data called?
Convolution
Why can an elevated creatinine level be a contraindication for IV contrast?
Creatinine is a waste product of muscle contraction that is normally filtered out of the body by the kidneys. Elevated creatinine levels may indicate impairment of the function of the kidneys.
What artifact results when the central tissues are interpreted to be less dense than they actually are and are incorrectly assigned lower CT numbers?
Cupping or Beam Hardening
What does DAC stand for?
Digital-To-Analog Converter
What do we call the precautions used when dealing with droplet infection transmission?
Droplet Precautions
What type of infection transmission involves contact of the conjunctivae or the mucous membranes of the nose or mouth of a susceptible person with large-particle droplets (larger than 5 um in size) containing microorganisms generated from an infected person.
Droplet Transmission
Why do most lesions of the heat enhance?
Due to a break in the normal blood brain barrier
During which of contrast enhancement are CTA images of optimal quality?
During the Bolus phase of contrast enhancement
During what phase of contrast enhancement is the agent's concentration in the veins similar to the concentration in the arteries?
During the equilibrium phase of contrast enhancement
When are most liver tumors the most conspicuous?
During the portal venous phase of liver enhancement
What is the fastest CT on the market?
EBCT
Rem and Sievert are a measurement of what?
Effective Dose" or "Dose Equivalent"
What is another name for Reconstructed Slice Thickness?
Effective Slick Thickness
On a multi-row detector scanner in which four slices are collected simultaneously, an un-stretched, contiguous helix would correspond to what pitch?
Either 4 or 1
What does EBCT stand for?
Electron Beam Computed Tomography
The increase in brightness on the CT image associated with tissues perfused by IV contrast agents is referred to as what?
Enhancement
T/F: The density of a barium sulfate suspension is diminished as it passes through the GI tract.
False
T/F: The image matrix does not affect the apparent noise or resolution of the resulting image.
False
Conventional radiography images tend to have better tissue contrast compared to CT localizer images.
False: CT localizer images have better soft tissue contrast than conventional images.
T/F: CTA is most commonly used in the evaluation of veins.
False: CTA is most commonly used in the evaluation of arteries
T/F: Cone Beam CT, used in oncology acquires up to 64 slices per rotation.
False: Cone Beam CT, used in Oncology, does not acquire individual slices, but instead collects data w/a large 2D panel to acquire the entire volume of anatomical information in 1 rotation.
T/F: Electrons are atomic particles that have a positive charge.
False: Electrons have a negative charge
T/F: For MDCT scanners, the slice thickness always affects the dose.
False: For MDCT scanners, the slice thickness does not affect the dose.
T/F: Increasing the number of photons increases the appearance of noise in the CT image.
False: Increasing the number of photons decreases the appearance of noise in the CT image.
T/F: In the range of energy levels used in CT, an increase in the kVp leads to a slight decrease in the radiation dose.
False: It leads to a slight increase in the radiation dose.
The image created when arcing occurs outside the tube within the oil contains streaks and noise.
False: No image is created when there is arching outside of the tube within the oil since no x-rays are produced
T/F: In general, sharp filters are used when examining predominantly low contrast regions, such as the abdomen and brain.
False: Sharp filters are used when examining predominantly high contrast regions, such as in musculoskeletal studies.
Slice thickness really only affects the dose to the patient on MDCT scanners.
False: Slice thickness really only affect the dose to the patient on single-row detector scanners.
T/F: The more an agent breaks down into a greater number of charged particles, the better it is tolerated.
False: The LESS an agent breaks down into a greater number of charged particles, the better it is tolerated.
T/F: The beam is more affected by beam hardening as it travels through the peripheral tissues and less affected by beam hardening as it penetrates the central tissues.
False: The beam is LESS affected by beam hardening as it travels through the peripheral tissues and MORE affected by beam hardening as it penetrates the central tissues.
T/F: the thicker, or more viscous the contrast media solution, the less force will be required to administer the solution into the patient.
False: The more force will be required
T/F: The pitch affects the amount of gap or overlap between slices.
False: The pitch does not affect the amount of gap or overlap between slices! The pitch indicates how the data is going to be collected and the reconstruction interval handles the location of the reconstructed slices.
T/F: The reconstruction process is equally successful at extracting bony surfaces and skin as it is at distinguishing fat, muscle, and other soft tissues.
False: The reconstruction process is usually much more successful at extracting bony surfaces and skin surfaces than at distinguishing fat, muscle, and other soft tissues whose CT numbers are much closer together.
T/F: Iodinated oral agents are more concentrated than iodinated IV agents.
False: They are less concentrated than iodinated IV agents
T/F: For a CTA examination, only the post-processed images are necessary for a complete diagnostic evaluation.
False; The post-processed images should be reviewed along with the axial images for a complete diagnostic evaluation.
T/F: Many more detectors are required in 3rd generation scanners than 4th generation scanners.
False; many more detectors are required in 4th generation scanners than 3rd generation scanners.
What is the beam geometry of a 4th generation system?
Fan Beam
3rd Generation Systems incorporate what type of beam geometry?
Fan Beam Geometry
How fast can a 3rd generation system acquire the data for one image?
Faster than one second per image.
Most CT systems today use a reconstruction method called _______ _____ __________.
Filtered Back Projection
What is the limit to the number of slices collected in a single rotation is you are going to be using filtered back projection to reconstruct the images?
Four Slices
What are the concentrations of iodinated oral agents?
From 6 to 9 mg of iodine per ml
What do we call the comparison of two imaging modalities yielding co-registered images?
Fusion Imaging
What are the two basic categories of detectors?
Gas and Solid State detectors
What is done by service personal to correct tube arcing from tungsten gas buildup?
Generally, the service personal will "burn off" the gas with specific service procedures in order to minimize the occurrence of arcing
What can be administered in order to inhibit gastric peristalsis?
Glucagon
To make sure that the reconstructed MPR images are diagnostic, it is important that the original slices do what?
Have no gaps between them.
What are the typical skin radiation doses for CT scans of the head, body and the localizer scan?
Head Scan 1-5 rads\nBody Scan 2-6 rads\nLocalizer Scan 0.05-0.1 rads
Since 1st Generation Scanners were so slow, imaging was limited to what part of the body and why?
Head because patient motion could be more easily controlled
What type of imaging technique should be used when post processing is required?
Helical Imaging.
What do helical artifacts look like?
Helical artifacts look like swirls or windmills on the image.
_______________ acts by constricting smooth muscle and venules, dilating arterioles, producing localized edema, accelerating heart rate, lowering blood pressure, and increasing gastric and mucous secretions.
Histamine
The black stripes in a CT Spatial Resolution Phantom represent the ______.
Holes
Who produced the first clinically useful CT scanner for brain imaging and when did he/she do it?
Hounsfield, in 1967
Enhances NADPH Oxidase Activity (2)\n\nPossible Answers: \nIFNγ, TNF, TGFβ, IFNα/β, CXCL8, CCL2, CCL11
IFNγ (from NKs, Th1 and Th0)\nTNF (from Macro and Th1)
Anti-histamines or steroids may be administered to a patient prior to an IV contrast injection in order to try to prevent or lessen the severity of which type of reaction mechanism?
Idiosyncratic Reaction Mechanism
What category of reaction mechanism can be caused by anything other than the properties of the contrast agent, the amount injected, or the injection rate?
Idiosyncratic Reaction Mechanism
What would make a contrast agent have a high viscosity?
If it's molecules are large.
On a single-row detector scanner, a pitch of 1 means what?
It means that the patient table moves a distance equal to the slice thickness during one rotation of the tube/detector assembly
What precautions are taken with diabetic patients?
If the patient is taking Metformin (Glucophage) they should be instructed to refrain from taking it for 48 hours following the procedure. Then, Metformin should be resumed only after kidney function has been reassessed and determined to be normal.
What is the only reason a technologist might consider changing the kVp for a given exam?
If the patient is very large or very small
The speed of EBCT makes it well suited for doing what?
Imaging the heart and coronary arteries.
In what electrical form does the amplifier output its signal/ information?
In Analog form
When is the only time that a patient's consent may be presumed rather than obtained?
In an emergency situation.
When is a lateral localizer image obtained?
In general, only if we intend to angle the gantry to specify oblique slices (e.g., for some head and spine studies)
How is spatial resolution measured?
In line pairs per cm
When and why was the ecessity for universal precautions first identified?
In the mid 1980s as a result of the HIV epidemic
When was EBCT originally designed?
In the mid-1980's
Where is the data stored after it leaves the DAC?
In the raw data file
Give an example of where cupping (beam hardening) might be evident.
In the supratentorium of the brain
Where does the radioactive pharmaceutical used in PET accumulate after it is injected?
In tissues having areas of rapid growth and increased metabolism
What is the In-Plane Spatial Resolution Formula?
In-Plane Spatial Resolution = Reconstruction (Display) FOV\nOVER\n# of pixels along each direction in the matrix\n\nor\nSpatial Resolution =__DFOV___ \nOVER\nThe Matrix
What is the easiest way to increase the number of photons?
Increase the tube current or the scan time.
What do we call the State laws that have been developed to govern communication between health care providers and patients?
Informed Consent Laws
When scanning the brachial plexus, it is advantageous to do what?
Inject in the arm which is contralateral to the side of primary interest in order to avoid streak artifacts.
_________ IV contrast agents divide into charged particles (called ions) when in a solution, like the patients blood stream.
Ionic IV contrast agents
What was it called when the Tube/Detector configuration in a 1st Generation Scanner scanned across the patient's body in a linear path before rotating and repeating?
It "Translated"
What does the display hardware do?
It assigns a specific gray level to the region of a CT image from which the attenuation information was detected.
What does the dose-optimized software do?
It automatically adjusts the mA
What does the "Space Charge Compensator" do?
It cools off the filament slightly as the tube voltage increases in order to prevent an unwanted elevation in tube current in response to higher kV levels.
In all actuality, what does the in-plane spatial resolution formula determine?
It determines the size of an object that can be seen in the resulting image.
What does oral contrast do besides just attenuating x-ray photons?
It displaces air and fluid in the bowels.
Describe a Cone Beam Artifact.
It has a "spoke" or "star-like" appearance around structures at the edges of the image. Structures at the center of the image are not affected.
What does a sharp reconstruction filter do?
It improves the definition of the edges of structures but it does not minimize the grainy or speckled appearance in the image.
What does an unacceptable Standard Deviation test indicate?
It is an indication of an increase in the image noise which could be caused by either a decrease in the delivered dose, resulting in a lower than expected signal, or an increase in image noise in the detector-amplifier chain.
Where is the photodiode located?
It is attached to the bottom of the solid state material on the detector.
What is believed to be responsible for reactions such as hypotension and hives?
It is believed that when an excessive amount of histamine is released in the body, the vascular system becomes overloaded and histamine passes into the surrounding tissues and causes hypotension and hives.
What is done to a xenon gas chamber in order to increase the chance of an incoming x-ray photon interacting with the gas inside?
It is pressurized up to 30 times the normal atmospheric pressure
What does the scan controller do?
It is responsible for the timing and operation of the table, gantry, and high voltage generator.
What is a threshold value/setting?
It is the value that we set in a 3D SSD rendering that is equal to the CT number of the tissue of which we want the surface rendering.
What does a smooth reconstruction filter do?
It minimizes the grainy appearance of noise in the image so that the contrast between tissues can be better distinguished, but is does not improve upon the edge definition.
What does BUN provide?
It provides information about the kidney's ability to remove impurities from the blood.
Explain the "filtered" in filtered back projection.
It refers to a filter that enhances certain characteristics in the raw data before back projection is performed.
What is the -3 to +3 acceptable limit for the CT Calibration Test referring to?
It refers to the fact that the CT number of water should be 0 (zero) but a variation of anywhere from -3 to +3 is acceptable.
What happens to a xenon atom when it is struck by a photon?
It splits into an ion and an electron.
If a tumor is more vascular than the liver, will it be brighter or darker than the liver in the arterial phase of the exam.
It will be brighter than the liver
How will increasing the window width change the representation of tissues on the image?
It will represent a wider range of tissues on the image.
When does the bolus phase of enhancement begin?
Just after the contrast agent is injected.
There is a __________ relationship between mAs and dose.
Linear
What is one way to tell if you have a faulty detector element?
Look at your AP or lateral localizer image and see if there is a straight line traced across the length of the image
How are MIP images generated?
MIP images are generated from the transverse slices of a CTA study by projecting the brightest pixels onto a plane.
What is the only way to enlarge the size of the image if the raw data is no longer available?
Magnification
Define Malpractice.
Malpractice is the failure to do something that a reasonable person, guided by those considerations which ordinarily regulate human affairs, would do.
What does MIP stand for?
Maximum Intensity Projection
Describe a metal artifact.
Metal artifacts frequently appear as streaks emanating from the metal object and are caused by a combination of beam hardening, the edge gradient effect, the partial volume effect, and motion
What is the best way to minimize metal artifacts?
Minimize the metal in the scan FOV
What can be done to help the barium sulfate solution to move through the GI system faster?
Mix some faster-moving iodinated oral contrast media with the barium sulfate solution.
What would we call an x-ray beam composed of photons all having the same energy level?
Monochromatic
Define Multi-Planar reconstruction.
Multi-planar reconstruction is a post-processing technique performed on image data which produces new slices from a set of CT scans.
In order to account for gaps or overlaps between adjacent slices there is another indicator of dose called the _________________________.
Multiple Slice Average Dose or MSAD
Define Negligence.
Negligence is a breach or failure to fulfill the expected standard of care.
Is there any need for back projection during the reconstruction process for a localizer scan?
No
Did Continuous Rotation and Multi-row Detector scanners come out at about the same time?
No; Multi-row Detector scanners came out years after continuous rotation scanners were the norm.
What appears in a CT image as a point-to-point fluctuation in the CT number within a uniform material?
Noise
What do we call it when a CT image looks grainy or speckled?
Noise
_____________ IV contrast agents do not divide into charged particles when in solution (like the patient's blood)
Non-ionic
Where is the CT x-ray tube mounted?
On the Rotating Frame Assembly within the gantry
Where is the raw data retained?
On the raw data storage device on the host computer
How many detectors were incorporated in the 1st generation CT Systems?
One
What happens to the xenon atom after it splits?
One side plate of each detector chamber has a positive charge and the other has a negative charge. After the collision the two charged particles migrate to the plate with the opposite charge and this can be measured as an electrical event.
How long are a patients archives normally held for?
One to seven years, depending on the state.
When should the veins on the dorsum of the hand be used?
Only if there is a lack of venous access to the vessels at the elbow or cubital fossa.
When should increasing the dose to the patient be considered?
Only when the result of no doing so would otherwise be a non-diagnostic study.
2nd Generation CT Systems used an x-ray tube that produced an x-ray beam that had a shape similar to what?
Opened paper fan
What are the key vital signs and their normal values?\nTemperature:
Orally 97˚ F to 99˚ F\nAxilla 96.5˚ F to 98.5˚ F\nRectal 97.5˚ F to 99.5˚ F
Define Osmolality.
Osmolality is the concentration of molecular particles in the contrast agent solution.
Define Out-Of-Field artifacts.
Out-Of-Field artifacts are characterized by image shading, streaks and incorrect assignment of CT numbers to the image pixels.
Describe out-of-field artifacts.
Out-of-field artifacts occur because the anatomy outside the scan field-of-view contributes toward the attenuation and hardening of the x-ray beam, but it is ignored during the image reconstruction process
What are the typically accepted values for PT, PTT and Platelet count?
PT = 10 to 14 seconds\nPTT = 20 to 40 seconds\nPlatelet Count = 150,000/mm³ to 400,000/mm³
What two tests asses the series of chemical interactions required to form a blood clot?
PT and PTT
What do we call the effect that results from the from the mathematical averaging of several millimeters of varying density tissues, which is displayed as a single shade of gray on the resulting image?
Partial Voluming
What artifact results from the mathematical averaging of various attenuation coefficients from several millimeters of different types of tissue?
Partial volume averaging
What determines the dose administered to a pediatric patient?
Patient weight and the type of scan to be done
What is the one responsibility of the patient?
Patients must take greater responsibility for maintaining good health.
What does PICC stand for?
Peripherally Inserted Central Catheter
When a solid state detector generates a flash of light, it is sensed by the ______________.
Photodiode
The anatomical coverage of a helical scan is determined by an important scan parameter called what?
Pitch
What can be increased to scan the vessel more quickly in a CTA examination?
Pitch
List the two possible formulas for determining pitch (scanner dependant)
Pitch = Movement of the patient table in one gantry rotation OVER\nTotal slice volume\n\nPitch = Movement of the patient table in one gantry rotation OVER\nThickness of a single slice
In reality, the x-ray photons generated by a CT x-ray tube have a variety of energies. This is referred to as being what?
Polychromatic
What do we call an x-ray beam that is comprised of a spectrum of energy levels?
Polychromatic
What does PET stand for?
Positron Emission Tomography
What is another name for post-patient collimation?
Pre-Detector Collimation
What might a facility do in order to prevent histamine reactions?
Pre-medicate with an anti-histamine or steroids.
What sensations may be experienced by the patient during the injection of interaarticular contrast?
Pressure, pain, tingling, or a feeling of fullness
What word associated with Computed Tomography is synonymous with the word "View"?
Projection
What does PHI stand for in regards to HIPAA.
Protected Health Information
Define Reconstruction Field Of View (RFOV)
RFOV is the region of interest illustrated in the resulting images and the FOV reconstructed from the complete set or raw data.
What do we call radiation that extends outside of the intended slice?
Radiation Penumbra
Data measured at each projection is placed in a computer file called the _____ ______.
Raw Data
What should you do if you see particulate matter in the IV contrast?
Read the label; it will tell you how to get rid of it or if the contrast needs to be discarded.
Reconstruction interval refers to how the helical slices are what?
Reconstructed
What does an elevated BUN indicate the possibility of?
Renal Disease
What are the key vital signs and their normal values?\nRespiratory rate:
Respirations/minute\nAdults 12-20\nChildren 15-30\nInfants 25-50
The array processor is also the site of calculations required to generate __________ ____________, and sometimes, to __________ image data.
Retrospective reconstructions, post-process
The _____________________ is located toward the central aspect of the gantry, about the perimeter of the gantry aperture.
Rotating Frame Assembly
What does a resolution test consist of?
Scanning a water filled phantom and determining the smallest line pair that can be resolved.
What is another name for solid state detectors?
Scintillation Detectors
What is another name for conventional scanning?
Serial Scanning
Each projection can consist of how many measurements coming from the detectors?
Several hundred
How many detectors are contained in a single detector array of a 3rd generation system?
Several hundred
What are the two basic types of reconstruction filters?
Sharp and smooth
What results from insufficient blood flow to the tissues and vital organs?
Shock
What is the approximate Skin Dose and Center Dose for 1 radiography film?
Skin Dose .5 rad\nCenter Dose 0.15 rad
What is the approximate Skin Dose and Center Dose for 5 radiography films?
Skin Dose 2.5 rad\nCenter Dose 0.75 rad
What is the approximate Skin Dose and Center Dose for a 30 slice CT study?
Skin Dose 5 rad\nCenter Dose 1 rad
Most continuous rotation scanners use ______________ technology.
Slip Ring
On most current CT systems, the ________ and _________ are also contained within the gantry.
Slip Ring, HVG (High Voltage Generator)
How should the slices from a CTA study be reconstructed?
So that they overlap
Which type of detector generates a flash of light in response to an incoming x-ray photon?
Solid State
What is the current detector of choice?
Solid State Detectors
Minimizing the noise with a large reconstruction FOV is attained only by compromising the image's __________________________.
Spatial Resolution
What is the formula for determining spatial resolution if the set of lines with 8 line pairs per centimeter can just be resolved??
Spatial Resolution = ___________10mm____________16 lines (there are 2 lines per pair)\n* Spatial Resolution = 0.625 *
Define Spatial Resolution.
Spatial Resolution is a measure of the size of the smallest object that can be visualized, or resolved, in an image.
What is another name for helical imaging?
Spiral Imaging or Spiral CT
In 1996 the definition and recommendations for Universal Precautions was revised and given a new name. What was that name?
Standard Precautions
What do we call the rules that all health care workers must follow in order to minimize the spread of infection?
Standard or Universal Precautions
Describe a streak artifact caused by motion.
Streak artifacts appear tangential to high contrast edges of the moving structure
Out-of-field artifacts may look like ______ or ________ on CT images.
Streaks or shading
What results from a lack of blood flow to the brain?
Stroke
The patient most often lies in the ________ position.
Supine
What are the key vital signs and their normal values?\nBlood Pressure:
Systolic Diastolic\nAdult 90-140 60-90\nChildren 85-130 45-85
mA is a measurement of what?
The "Filament Current"
What is the minimum amount of time that must transpire between the end of one scan and the initiation of the next scan called?
The "Inter-scan Delay Time"
What do we call the voltage applied across the anode and the cathode?
The "Tube Voltage"
What was the major difference in the configuration between 2nd and 3rd Generation Systems?
The 3rd Generation detector array in a curved arc rather than a straight line.
In which system component is data calculated into an image?
The Array Processor
Where is the primary place for all complex mathematical calculations involved in generating CT images?
The Array Processor
Which vein is the vessel of choice for injecting IV contrast media?
The Basilic Vein
The ___________ is an indicator of radiation dose which includes the radiation located within the intended slice thickness as well as that from the penumbra.
The CT Dose Index or CTDI
Which vein drains the dorsal part of the hand, and runs between the pectoralis major and the deltoid muscles, through the clavipectoral fascia and finally joins the axillary vein?
The Cephalic Vein
The ARRT Standard of Ethics is comprised of what?
The Code of Ethics and the Rules of Ethics.
What gantry component collects the attenuation information?
The Detectors
What CT System Component is responsible for converting the digital signal into an analog form?
The Digital-To-Analog Converter or DAC
Tumors of the liver typically receive their blood supply from which vessel?
The Hepatic artery
What CT System Component is necessary to produce the high voltage potential that exists between the cathode and the anode?
The High Voltage Generator
What CT System Component translates each command as it is entered into the systems machine language before passing it on to the Scan controller?
The Host Computer
What component controls the storage devices such as hard disks and removable media?
The Host Computer
What system component is the primary link between the technologist and the other components of the imaging system?
The Host Computer
The CT number scale is also referred to as what?
The Hounsfield scale
Which is better, a laser camera printer or a multi-format camera printer and why?
The Laser Camera Printer is better because the laser camera creates less scattered light which produces superior, high-contrast images compared with multi-format cameras.
What console component serves the purpose of providing feedback to the technologist and data entry?
The Monitor
During what phase of contrast enhancement does the bolus start to disburse into the capillaries, and then into the veins?
The Non-Equilibrium Phase
During which phase of contrast enhancement do we generally obtain the best differentiation of structures in the soft tissues as a result of contrast injection?
The Non-Equilibrium Phase
What system component is the key point of interaction between the technologist and the imaging system?
The Operators Console
Where does the liver receive most of its blood supply from?
The Portal vein
What do we call the thickness of the final image?
The Reconstructed or Effective Slice Thickness
In a helical scan, what determines weather the slices will be contiguous or if there will be a gap or an overlap of slices (images)?
The Reconstruction Interval
What do we call the time required for the tube and detectors to rotate a complete 360˚?
The Rotation Time
What determines the number of detectors collecting data for a particular scan?
The SFOV
How large should the SFOV be and Why?
The SFOV should be large enough to cover all of the patient anatomy. If any part of the patient lies outside the SFOV, out-of-field artifacts will occur.
What determines the total area over which projection data is collected?
The Scan Field Of View (SFOV)
What are the acceptable limits for CT Number Standard Deviation?
The Standard Deviation of water must not exceed a level specified by the manufacturer.
What do we call the flow of electrons from cathode to anode?
The Tube Current
What do we call the voltage that is applied across tha anode and the cathode?
The Tube Voltage
What is the only part of the tube that passes x-rays?
The Tube Window
What controls how "contrasty" the image appears?
The Window Width
Which type of detector provides it's own inherent post-patient collimation and why?
The Xenon Gas detector- Because of its relative insensitivity to x-rays striking it at severe angles
The severity of the out-of-field artifact depends on what?
The amount and density of the anatomy outside the SFOV
What usually determines the amount of table incrementation selected?
The amount of table incrementation selected usually depends on the size of the structures that need to be visualized in the clinical study.
How will arcing within the tube manifest itself during the early stages of tungsten gas formation?
The arcing will be infrequent and not of great energy, therefore only slight signs of random noise or streaks begin to appear in the images.
Administration timing and dose of barium sulfate agents are largely dependent upon what?
The area to be opacified
What CT x-ray tube component makes thin slice, high resolution imaging possible.
The availability of a small focal spot, which comes from having/using a small filament.
What are the two parameters evaluated during the CT number calibration test/CT number standard deviation test?
The average value of the CT numbers and the standard deviation of the CT numbers within a region of interest.
What does the window level control?
The brightness of the image. Specifically, the window level sets the center CT number displayed on the monitor.
Where does the calculated image go to after it leaves the Array Processor and what for?
The calculated image goes to the Host Computer so that it may be maintained on a storage device and displayed on the console monitor.
How do colon carcinoma metastases in the liver appear in relation to the liver itself?
The colon carcinoma metastases in the liver are less vascular than the liver
Describe the detector arrangement in a 4th generation CT system.
The detectors do not travel with the tube but instead form a complete circle around the gantry in a ring configuration, which nutates or angles during the scanning process.
Define Patient Dose.
The dose is the amount of ionizing radiation absorbed by the patient per unit mass.
Describe the edge gradient effect.
The edge gradient effect occurs when different distinctly different attenuation coefficients are obtained for the same object depending on the vantage point of the projection. This leads to uncertainty in the reconstruction process and manifests itself as streaks which emanate from structures having sharp edges and great differences in density from neighboring tissues
What do we call the hole in the gantry where the table is fed through?
The gantry "Aperture"
What is the main source of the enormous amount of heat that builds up in a CT x-ray tube?
The generation of x-rays from the collision between the electrons and the anode target.
What would happen if you did not filter the back projection?
The image would have blurry edges and appear very "grainy" or "noisy"
What determines weather consent may be given verbally or if it must be given in writing?
The individual State Laws
What was the single most important advancement that led to the development of helical imaging?
The introduction of continuous rotation scanners
What is the major drawback to volume rendering?
The large computational requirements
What is the factor that is responsible for the amount of noise we see in the image?
The mAs
What are the advantages of plastic-sheathed needle/ catheter combinations over butterfly-type needles?
The needle/catheter combination allows for greater rates of injection and has a greater tendency of staying in the vein, minimizing the occurrence of extravasation or injection directly into the soft tissue.
How many detectors are contained in a 3rd Generation Systems detector array?
The number of detectors in a 3rd Generation Systems has ranged from several hundred to several thousand.
What do we access in order to generate Retrospective Image Reconstructions?
The patient's raw data files
What is the definition of pitch on a single-row detector scanner?
The pitch equals the movement of the patient table in one gantry rotation divided by the slice thickness.\nor\nPitch = Movement of the patient table in one gantry rotation Slice Thickness
How does the slice thickness affect noise?
The pre-patient collimation allows more photons to reach the detectors when a thick slice is selected that when a thin slice is selected. So a thicker slice appears less noisy because there are more photons detected relative to the noise level in the thicker slice.
Define Quality Assurance
The procedure of performing specified tests or measurements on a periodic basis in order to assure that a set level of quality, as specified by the system manufacturer, has not been compromised.
When dealing with strictly x-rays, what is the most common unit for measuring absorbed radiation dosage?
The rad
What is believed to contribute to pain associated with vessel dilation, as well as flushing, changes to red blood cells, vascular endothelium damage, vomiting, nausea, and dehydration; and what type of reaction mechanism category would this fall under?
The rapid movement of fluid, especially water, through the vascular system. This would fall under the Chemotoxic Reaction Mechanism category.
What is the primary function of the array processor?
The reconstruction of the projected attenuation raw data into a CT image
What single aspect of 2nd Generation Scanners led to applications outside the head?
The reduced scan time. (From 5 minutes on a 1st Generation Systems to 20 seconds per image on a 2nd Generation Systems)
What side of the heart receives blood returning to the heart threw the superior and inferior vena cava?
The right side of the heart.
What governs who can administer IV contrast?
The rules governing who can administer IV contrast media vary from state to state.
What determines which filament is actually used in an exam?
The size of focal spot that is required for the exam
What is the slip Ring?
The slip ring is a large rotating ring which surrounds the gantry aperture and, by means of electrical brushes, conveys electrical power and data to the components mounted on the rotating ring.
What to we consider a minor reaction?
Those that last briefly tend to cause the patient only minor discomfort and generally do not require any treatment.
Why would using a smaller detector aperture help minimize the edge gradient effect?
The smaller the detector aperture, the lower the probability of capturing photons that have been attenuated to different extents by the same material
During a myelographic study, what space is the Intrathecal contrast injected into?
The subarachnoid space.
Which system Components operate using analog waveform?
The table, gantry, and high voltage generator.
1st Generation: What happens next after a complete translation from one side of the patient to the other?
The tube/detector assembly rotates about the patient 1 degree and another translation commences so that another "projection" can be measered.
What are the two most notable components located in the gantry?
The xray tube and the detectors
What characterizes the Non-equilibrium phase of contrast enhancement?
There is a 10 to 30 HU density difference between the abdominal aorta and the inferior vena cava.
What characterizes the equilibrium phase of contrast enhancement?
There is a density difference of less than 10 HU between the abdominal aorta and the inferior vena cava.
What defines the bolus phase of enhancement?
There is a significant density difference between the abdominal aorta and the inferior vena cava.
What causes the basilic vein to remain more stationary than the cephalic vein when starting an IV in the cubital fossa?
There is an anastomosis between the basilic and cephalic veins at the elbow which helps the basilic vein to remain quite stationary within the subcutaneous tissue.
What do all IV contrast agents have in common?
They all contain iodine
What do the detector elements do?
They measure the attenuation information coming out of the patient and convert it into tiny electrical signals that are then sent to the amplifier.
What do pre-patient collimators do in single-row detector scanners?
They restrict the x-ray beam to the thickness of the slice.
What do pre-patient collimators do in multi-row detector scanners?
They select the thickness of the x-ray beam, which spreads out over multiple detectors.
How should you treat a patient experiencing shock?
They should be kept warm with legs elevated (provided there are no bleeding wounds in the upper body or head). If it is anaphylactic shock a medication such as epinephrine can be administered.
How do beam hardening correction algorithms work?
They use idealized models of patients composed of fat, muscle, fluid, and bone, but since few patients perfectly match the composition of the model, inaccuracies may result in the correction process
Why might a patient swallow a final dose of water after consuming the barium or iodine solution?
This keeps the gastric contents from being opacified and allows evaluation of the gastric wall.
Describe a bi-phasic liver study.
This study collects two complete sets of slices through the liver during two different periods within the non-equilibrium phase of enhancement.
What do we consider a moderate reaction?
Those that are a bit more serious, which may require treatment and close observation, although hospitalization is typically not required.
In the early days of 3rd generation scanners, before the invention of continuous rotation scanners, shy was it necessary to stop the gantry frame from rotating at the end of every scan and then reverse the direction of the gantry frame's rotation for the next scan?
To prevent the high-tension cable going from the High Voltage Generator to the tube from winding up
What was the purpose of the added detectors (detector array) and the fan beam geometry in the 2nd Generation design?
To reduce the amount of time required to collect data.
Why were the ARRT Rules of Ethics created?
To safeguard the patients comfort and safety
Why were continuous rotation scanners introduced?
To speed up the exam process
Where is the tiny electrical signal output from the detector elements sent?
To the Amplifier
Where does the analog signal go to after it leaves the amplifier component?
To the Sample-and-Hold Component (S/H)
What are the thick, metal pre-patient collimators attached to?
To the bottom of the tube housing
How accurately should temperatures be recorded?
To the nearest tenth of a degree
Direct acquisition of the oblique slices may be collected when the gantry is oriented in an orientation between ______________ and _____________.
Transverse and Coronal
Arching in the oil will almost always cause the high voltage generator to shut down due to excessive current.
True
Generally speaking, agents have a greater osmolality than blood plasma.
True
Iodinated contrast agents do not cross an intact blood brain barrier.
True
T/F: "Reconstruction Interval" is a scan parameter that is specific to helical scans only.
True
T/F: 3rd and 4th generation systems use different approaches to achieve similar results.
True
T/F: 4th generation systems did not necessarily represent a design which was more advanced than 3rd generation systems or that offered improved clinical benefits.
True
T/F: A build-up of air bubbles or other gasses within the oil surrounding the x-ray tube will create an electrically conductive path for the high voltage potential.
True
T/F: A finer reconstruction interval may be used for helical data than would be practical with conventional overlapping slices.
True
T/F: A large matrix increases the appearance of image noise.
True
T/F: A nasogastric tube may contain metal and should not be removed for a CT scan.
True
T/F: A retrospective reconstruction requires the raw data.
True
T/F: A thinner acquired slice thickness means that smaller detectors are being selected.
True
T/F: A very viscous agent may contribute to discomfort at the injection site.
True
T/F: After arcing occurs outside of the tube in the surrounding oil, it is possible that after allowing the tube to cool and resetting the generator, scanning could be continued, although not recommended.
True
T/F: As a Technologist you must be a patient advocate first and an assistant to the physician second.
True
T/F: As a Technologist, you are responsible for your own negligent acts, regardless if another medical professional advises you to act in the negligent fashion.
True
T/F: Barium sulfate solutions are known for passing threw the GI tract slowly.
True
T/F: Beam hardening correction algorithms are a standard feature on most CT scanners today.
True
T/F: Collecting multiple slices at the same time on a MDCT scanner delivers more dose to the patient than does conventional or serial scanning.
True
T/F: Cone Beam CT is being used in dental and scientific imaging.
True
T/F: Cone beam reconstruction also applies a reconstruction filter in order to improve the edge definition of structures or to minimize the appearance of noise.
True
T/F: Contrast media helps delineate tissues and pathology.
True
T/F: Conventional CT yields the best image quality which is free from helical artifacts.
True
T/F: Different manufacturers use one of two different formulas for determining the pitch of their scanners.
True
T/F: EBCT does not use an x-ray tube.
True
T/F: If back projection was applied to the raw data without convolution, the tissues I the resulting image would have blurry edges and they would be difficult to differentiate because they would appear grainy or noisy.
True
T/F: If rather than two discrete locations, the tissue being scanned gradually becomes displaced over the period of the scan, the resulting images will depict the motion more like a blurring of the tissues rather than a "ghosting artifact".
True
T/F: If the anatomy extends beyond the scan field-of-view, out-of-field artifacts may occur.
True
T/F: If the veins of the hand are used, a smaller catheter and slower injection rate than typically used will be required.
True
T/F: If there is a discrepancy between the study ordered on the paperwork and the one described by the patient, further clarification must be sought.
True
T/F: If there is a risk of aspiration, iodinated oral agents are contraindicated.
True
T/F: In a 3D SSD, only the tissues selected according to their threshold values will be displayed. All other CT numbers and their corresponding tissues will be ignored.
True
T/F: In patients with diabetes or renal insufficiency, a low osmolar, non-ionic contrast agent is safer for the kidneys.
True
T/F: In some states, for procedures that entail greater risks, informed consent may only be obtained by a physician.
True
T/F: In the early days of 3rd generation systems, the high voltage generator was large and heavy and was safely fastened to the floor in the exam room.
True
T/F: Increased injection rates are also associated with an increase in instances of adverse reactions.
True
T/F: Inter-scan delay times include idle time between scans to allow tube cooling.
True
T/F: Interpretation and diagnosis are outside the scope of practice for the profession.
True
T/F: Intrathecal contrast is not normally administered in the CT department, but may be encountered there.
True
T/F: Keeping the stomach free from oral contrast media enables better visualization of abnormalities on the stomach wall.
True
T/F: Laser cameras do not require a photographic focusing lens.
True
T/F: MIP images are most useful when depicting relatively simple anatomy in which there is little superimposition of structures.
True
T/F: Magnification does not affect the spatial resolution or affect the appearance of image noise.
True
T/F: On MDCT scanners, a retrospective reconstruction is commonly used to modify the reconstructed slice thickness.
True
T/F: On a 3rd generation scanner, if there is a problem with a single detector, it will be represented as a ring on the CT images.
True
T/F: On a MDCT Scanner, the reconstructed or effective slice thickness must be equal or greater than the acquired slice thickness.
True
T/F: One benefit of helical scanning is that a smaller amount of contrast media may be used for many procedures.
True
T/F: Oral contrast agents are sometimes administered rectally in order to reach the distal GI tract.
True
T/F: Overlapping slices may provide more thorough coverage of the anatomy than contiguous slices.
True
T/F: PHI may legally be used for activities such as teaching, business and management operations, disclosures required by law, and public health and other governmental reporting.
True
T/F: Pet images are very sensitive to changes in metabolism associated with malignant tissues but have very poor resolution.
True
T/F: Platelets are small cell fragments that do not contain a nucleus.
True
T/F: Pre-patient collimation is a factor in determining the slice thickness in single-row detector CT, but not in MDCT.
True
T/F: Since a single projection is used, there is no need for a complex reconstruction technique on localizer images.
True
T/F: Smooth filters are preferable when examining low contrast regions, such as the abdomen and brain.
True
T/F: Solid state detectors have been used on both 3rd generation and 4th generation scanners.
True
T/F: Structures in the center of the image are not affected by the cone beam artifact.
True
T/F: The ARRT does not review, evaluate, or endorse publications.
True
T/F: The CTDI does not factor in the variation in dose due to gaps or overlaps in adjacent slices.
True
T/F: The MIP technique may require extensive editing to remove dense anatomic structures (bones), which would otherwise obscure the vessels of interest.
True
T/F: The attenuation of on x-ray beam is highly dependent upon the energy of the x-ray photons.
True
T/F: The collision between the photon and the detector atom occurs much closer to the surface in a solid state detector than a xenon gas detector.
True
T/F: The further the CT Tube is situated from the patient, the lower the absorbed dose.
True
T/F: The kidneys have a harder time clearing large particles from the blood than small particles.
True
T/F: The localizer image has limited resolution due to the size and spacing of detector elements, and requires longer exposure times than conventional radiography.
True
T/F: The localizer image has limited resolution due to the size and spacing of detector elements.
True
T/F: The mAs does not affect the image contrast or resolution.
True
T/F: The more slices collected by the MDCT scanner in a single rotation, the less the penumbra effect adds to the total patient dose.
True
T/F: The reconstruction algorithms used to generate the images in CT can not always accurately represent very dense objects (like metal) and interfaces.
True
T/F: The reconstruction or display FOV is always equal to or smaller than the scan FOV.
True
T/F: The signal from both xenon and solid state detectors must be amplified.
True
T/F: The size of a solid state detector is about the same size as a xenon gas detector.
True
T/F: There are no parameters on the scanner that directly allow us to decrease the amount of noise.
True
T/F: There is no pattern or regularity to the appearance of the artifact caused by arcing within the tube.
True
T/F: Today there are very few scanners that use 4th generation technology.
True
T/F: Vascular depiction is most accurate with a narrow VOI.
True
T/F: When PET and CT are fused, the studies can occur on different days.
True
T/F: Xenon gas detectors cannot be used in 4th generation systems.
True
T/F: as the slick thickness increases, the for the exam as a whole decreases.
True
T/F: for virtual colonoscopy studies, we do not want to opacify the bowel with an agent.
True
T/F: in general, the window level is set equal to the CT number of the tissue of interest.
True
T/F: kVp affects both the dose to the patient and the image noise.
True
T/F: kVp is usually only decreased to minimize dose in small patients.
True
T/F: noise makes it difficult to see subtle contrast differences or fine details.
True
T/F: with advances in computers, computational requirements are nolonger a significant drawback and for many applications, volume renderings the preferred method of display.
True
T/F: within the range determined by window width, the CT numbers are equally distributed from black to white.
True
There is no federally imposed limit to radiation exposure.
True
True/False: In regards to 2nd Generation Systems, the tube/detector assembly still translated across the patient during the collection of a "projection" of data.
True
What is located on the surface of the rotating anode?
Tungsten
How far can droplets travel?
Up to 3 feet
The CT numbers and the resultant grey levels are based on what?
Upon the linear attenuation coefficient for a voxel of tissue
What is the most accurate way to determine delay times when dealing with pediatric patients?
Use bolus tracking software or perform a test bolus timing scan
How can we minimize the partial voluming effect?
Use thinner slices
What reconstruction option reconstructs the inside of surfaces of pathways such as the bowel, bronchi and the sinuses?
Virtual Endoscopy (a form of 3D SSD)
Define Viscosity.
Viscosity is a measure of the "thickness" of a liquid, related to the frictional forces of the molecules of the substance as they flow past one another.
In which type of 3D rendering is each voxel in the data set assigned an opacity value as a function of its density?
Volume Rendering (VR)
What does VOI stand for?
Volume of Interest
What is another name for helical or spiral CT?
Volumetric CT
The CT number scale is established relative to the attenuation of what?
Water
What is an important consideration when printing CT images, especially when they are the images to be interpreted by a Doctor/Radiologist?
We must ensure that the image printed on the film looks identical to the one displayed on the monitor.
Describe how a solid state detector works.
When a photon strikes the solid state material, it emits a flash of light which is converted into an electrical signal by a photocathode.
When are the most accurate MIP results obtained?
When a small volume of interest is selected
When is iodinated oral contrast agent used?
When barium sulfate agents are contraindicated
When might tube arcing occur outside of the tube?
When impurities cause the oil to become electrically conductive
When might tube arcing occur within the tube?
When the tube vacuum is compromised
When is a wide window width generally used?
When viewing structures with a high degree of contrast, such as in the lungs. (Stark differences in density of tissues)
When is a narrow window width useful?
When visualizing structures exhibiting subtle inherent contrast, such as with the soft tissues of the brain. (Similar differences in density)
How do we accommodate the limitations of only being able to display 256 shades of grey and only being able to see about 20?
Window Width (WW) and Window Level (WL)
Define Window Width.
Window width refers to the range of CT numbers displayed on an image and it adjusts how "contrasty" the image appears.
Most gas detectors used on CT systems contain a gas called _________.
Xenon
What are you doing when you magnify an image?
You are simply enlarging the individual pixels of the reconstructed image for display purposes.
The use of thicker slices reduces the resolution along the direction perpendicular to the _____________ direction.
Z-direction
On single-row detector scanners, the collimated x-ray beam thickness equals the ____________ _______ ____________, which also equals the final ________ ___________.
acquired slice thickness, image thickness
The ARRT Standard of ethics is ____________.
aspirational
The iodine in the contrast media increases the ___________ of the x-ray photons.
attenuation
The degree of beam hardening is dependant upon the ______________ being penetrated and its _______________.
body part, composition
Tissues perfused by IV contrast media appear ________ on CT images.
brighter
In addition to the cupping artifact, beam hardening may be manifested by ______ ________ and regions of decreased density near _______, or through ________ body parts.
broad streaks, bones, thick
On a single row detector scanner, the slice thickness is determined by the _______________ of the ___________.
collimation of the x-ray beam
If the reconstructed interval is equal to the slice thickness, te reconstructed slice will be _______________.
contiguous
Changing the kVp of the scan involves a tradeoff between _________, ______ and apparent _________.
contrast, dose and apparent noise
Beam hardening is sometimes called _________ because the signal intensities of tissues on the resulting image have the appearance of the contour of a cup.
cupping
Some of the more sophisticated multi-planar reconstruction programs even allow a/an_________ ___________ to be placed on the original set of images
curved cut-line
By using thicker slices to cover the same anatomy, the radiation dose to the patient may be _____________.
decreased
There is a __________ correlation between the apparent noise level and the _______ ___ __________ used in making the image.
direct correlation, number of photons
When starting an IV, to get a better view of the vessels we have to work with, we need to __________ the vessels by applying a tourniquet.
distend
Since the liver has a/an __________ blood supply, the ________ of the scan following the start of the injection is crucial.
dual, timing
On single-row detector scanners, as the pitch is increased, there is an unfortunate increase in the ___________ ________ _____________.
effective slice thickness
The ARRT Rules of Ethics are __________ policies that are _________, if ___________.
enforceable, punishable, if violated
To get contiguous slices, the table increment must be ________ to the slice thickness.
equal
When scanning an abdomen, it is important to complete scanning before the organ of interest has reached the ______________ phase of enhancement.
equilibrium
The number of photons measured by the detectors is reduced in an ______________ fashion as the thickness of the tissue traversed is increased.
exponential
The cathode of most CT x-ray tubes contains more than one __________, each with a __________ __________.
filament, different length
For a ________ ______, projections are made throughout the ____________ _____ rotation.
full scan, complete 360˚
Each pixel in the image is assigned a ________ ________ __________ according to the CT number calculated by the___________ _________ ______________.
gray scale number, filtered back projection
The _________ the distance traveled through the tissue and the ________ the tissue the x-ray photons penetrate, the more the dose is decreased along the photons' path.
greater, denser
The MSAD is _________ than the CTDI when the slices or loops of the helix overlap and the MSAD is ___________ than the DTDI when there are gaps
greater, lower
2nd Generation Systems contain a/an __________ of detectors referred to as a/an_______________?
group, detector array
If the pitch is increased to more than 2 (i.e., in one rotation the patient table moves more than twice the total slice volume) ____________ artifacts will occur.
helical
A _________ _____ allows for continuous data collection during continuous patient movement through the gantry.
helical scan
The amount of time that each injection takes is directly related to the __________ _________, the _____________________________, and the ____________________.
injection rate, volume of the injection, velocity of the blood flow
If scanning is performed in the liver later than the portal venous phase, in the equilibrium phase, many hepatic tumors become ___________ with the liver tissue and may not be visible on the images.
isodense
The beam is hardened _______ by fat and _______ by bone.
less, more
Most tumors are _________ (more/less) vascular than the liver itself and will be most obvious during the _________ ______ phase.
less, portal venous
Higher CT numbers (i.e., dense structures) are assigned __________ shades of gray and lower CT numbers (i.e., structures which are not dense) are assigned ________ shades of gray.
lighter, darker
Non-ionic contrast belongs to the ______ Osmolar category of IV contrast.
low
The ______ is the tube current. The _______ is the product of tube current and time.
mA, mAs
What are the normal ranges in CT for mA and kVp?
mA: Tens to Hundreds of mA\nkVp: 90-140kVp
There is a tradeoff between __________ the image quality and ___________ the patient dose.
maximizing, minimizing
Blood vessels and vascular tumors appear __________ (more/less) dense than lymph nodes when IV contrast media is used.
more
A smaller set of hepatic tumors is ________ (more/less) vascular than the liver, however, and may only be visible during the ________ ________ phase.
more, hepatic arterial
The use of thick slices produces an effect called ____________ _____________ or _____________ __________ ____________.
partial voluming, partial volume averaging.
Each ______ of a volume rendered image represents the sum of the contributions of each _______ along a ____ passed through the image data set.
pixel, voxel, ray
Maximum intensity projection images are generated by projecting the highest _____ values from a _____ of CTA axial images along many ____ onto a single ______.
pixels, stack, "rays", image
The Localizer scan is similar to a ______ ________ radiograph.
plain film
The thickness of the x-ray beam in a helical study is determined by the ___________ _____________.
pre-patient collimation
Each time the tube arcs, the ___________ data for that view is distorted.
projection
The quality of x-rays emitted from the anode target is _________ to the number of electrons which stream from the __________ to the anode.
proportional, filament
Radiation strictly from x-rays is measured in _____ or ______. Sv and rem are used to measure ________________ radiation.
rad or Gy (Gray), any kind of
Increasing the overlap of the reconstructed slices increases ____________ and ____________ the effects of partial volume averaging.
resolution, decreases
Violating the ARRT Rules of Ethics is subject to ___________.
sanctions
Contrast media is used to improve the ___________ and the ____________ of clinical diagnosis.
sensitivity, specificity
Arcing of the tube through the oil in the x-ray tube housing is very ________ and ___________.
severe and destructive
Unlike conventional radiography, CT uses a ______ __________ film.
single emulsion
for a CTA exam, ______ slices are collected in the direction of the __________.
thin, blood flow
The tube/detector array in a 3rd Generation Systems no longer _____________ as a 1st and 2nd Generation Systems but simply __________ around the patient.
translates, rotates
The rotating frame assembly contains the _________, ____________ and the ___________.
tube, detector array, data acquisition system (DAS)
As the VOI from the helical image data included in the MIP increases, the apparent _________ __________ on the MIP image may decrease. This effect is most pronounced with ______ vessels and may even simulate _________________.
vessel diameter, small, vessel occlusion
During the CT scan, the patient should be monitored both __________ and ____________.
visually and verbally
In helical imaging, the path of the x-ray beam is determined by the thickness of the _______ ________ and the speed of the _________ _______.
x-ray beam, patient table
What are some other features for minimizing the radiation dose to the patient found on new CT scanners?
• "Noise Reduction Algorithms\n• Improvements in the efficiency of the detectors
What are some signs of shock?
• Altered levels of consciousness\n• Hypotension\n• Cool bluish or grayish skin tone\n• Tachycardia\n• Restlessness
Why would you instruct the patient to be NPO for several hours before the CT study, with the exception of an oral contrast?
• An empty stomach allows for better diagnostic evaluation\n• Fasting reduces peristalsis which can cause motion artifacts\n• An empty stomach is beneficial should the patient become nauseous or vomit after receiving the contrast agent
Where may the edge gradient effect be seen?
• At the interface of bone and soft tissue\n• At the interface of air and contrast media\n• Sometimes from the edge of the patient table
What structures normally enhance during administration of IV contrast for a CT of the head?
• Blood vessels\n• Choroid plexus\n• The Dura
What body substances does standard precautions apply to?
• Blood\n• Body Fluids\n• Secretions\n• Excretions (except sweat)\n• Non-Intact Skin\n• Mucous Membranes
A delayed scan of the pelvis after injection of IV contrast may be required in \norder to visualize what?
• Cancer of the prostate\n• Cancer of the ovaries\n• Cancer of the uterus
What are some contraindications to using barium sulfate?
• Colon obstruction\n• Perforation\n• Tracheosophageal fistula\n• Obstructing lesions of the small intestine\n• Pyloric stenosis\n• Known hypersensitivity to barium sulfate
What are some indications for a CT of the abdomen?
• Detection of masses\n• Lesions\n• Vascular abnormalities\n• Trauma
What are some conditions that call for non-ionic contrast media?
• Diabetes\n• Functional diseases of the liver and kidneys
What are the most frequent adverse reactions to barium sulfate?
• Diarrhea\n• Abdominal Cramping\n• Colon Impaction (rare)\n• Barium Granuloma\n• Barium Appendicitis\n• Intestinal perforation\n• Peritonitis
What are the procedures for a post-myelographic CT?
• Elevate Head\n• Confirm density of the contrast media\n• Ensure that contrast media does not separate from the CSF
What are some limiting factors to the in-plane spatial resolution?
• Focal Spot Size\n• CT Scanner Geometry\n• Detector Size\n• Reconstruction Algorithm
What are the geometric factors of the scanner that affect spatial resolution?
• Focal spot size\n• Detector aperture size\n• Focal spot to patient distance\n• Patient to detector distance
List the Contact Precautions.
• Gloves and Handwashing\n• Wear a Gown\n• Wear Gloves and gown during transport
What are some of the more common standard precaution procedures?
• Handwashing\n• Gloves\n• Mask, Eye Protection, Face Shield\n• Gowns\n• Sterilizing Equipment\n• Linens\n• Needles\n• Patient placement
Interaarticular contrast may be administered prior to CT evaluation of which joints?
• Hip\n• Knee\n• Ankle\n• Shoulder\n• Elbow\n• Wrist\n• TMJ
When may IV contrast be used in a CT examination of the chest?
• In evaluating masses of the chest\n• Lymphoma\n• Hilar or cardiac masses\n• To visualize vessels\n• Pulmonary emboli
What are some signs of a stroke?
• Inability to communicate\n• bilateral or unilateral numbness or paralysis\n• Pupil disparity\n• Incontinence\n• Hypertension
What are the benefits of oral contrast?
• It helps reduce the risk of misdiagnosing fluid-filled bowel as an abscess or tumor\n• It helps to visualize is a lesion is exterior to the bowl or whether it infiltrates the bowel
What can cause shock?
• Loss of blood volume\n• Sudden massive vasodilation
List the Droplet Precautions.
• Maintain at least 3 feet between infected patients and other patients\n• The door may remain open\n• Wear a mask when working within 3 feet of the patient\n• Mask patient during transport if possible
What should be done when a patient has a stroke?
• Monitor vital signs frequently\n• Prepare patient for airway ventilation, suction, intravenous fluids and possible CPR
A delayed scan of the brain after injection of IV contrast may be required in order to visualize what?
• Multiple Sclerosis\n• Metastatic lesions\n• AIDS-related abnormalities
What are some reasons for evaluating the arteries with CTA?
• Narrowing caused by atherosclerosis\n• Aneurysms \n• Dissections\n• Traumatic injury\n• Congenital vascular anomalies\n• Effects of vascular treatments
List the Airborne Precautions.
• Negative air pressure in room (6 to 12 air changes per hour)\n• Wear N95 respirator into room\n• Place mask on patient if transport is necessary
How do you identify Cardiac Arrest?
• No Pulse\n• No respiration\n• Vomiting\n• Seizure\n• Damp bluish or grayish skin tone\n• Incontinence or defecation
What factors come into play when deciding upon a particular contrast agent?
• Patient Tolerance\n• Patient History\n• Method\n• Rate of Administration\n• Cost\n• Radiologist preference
As a result of radiation exposure during pregnancy, there is an increased incidence of what?
• Prenatal deaths\n• Abnormalities\n• Mental Retardation\n• Neonatal Deaths due to complications
What conditions require scanning of the pelvis immediately following the injection?
• Prostate and ovarian cancer\n• Lymphoma\n• Melanoma
What are some other ways to minimize dose?
• Reduce repeat scans\n• Reformat rather than re-scan\n• Reduce multiple scans
What parameters affect patient dose?
• Scan rotation time\n• The tube current,\n• The peak tube voltage\n• The slice thickness\n• The table increment\n• The pitch\n• The anatomical coverage desired
What could cause a patient to have a diminished cardiac output?
• Shock\n• Compromised blood flow
What are some of the parameters that we directly control that affect spatial resolution?
• Slice thickness\n• Display FOV\n• Image Matrix\n• The Reconstruction Filter
What are some other tests performed on a less frequent basis by the service representative or site physicist? (11 items)
• Spatial Resolution\n• Contrast Resolution\n• Table Accuracy\n• Dose\n• Accuracy of spatial measurements on the image\n• Consistency of CT numbers across the image\n• Linearity of the gray scale of the image as it relates to the actual density of tissues measured\n• Radiation scatter and leakage\n• Slice thickness accuracy\n• Fidelity of the video monitor\n• Film output
What does the Reconstruction or Display FOV affect?
• The apparent zoom level in the image\n• The appearance of noise\n• The in-plane resolution of the image
What affects the severity of the metal artifact in the resultant images?
• The quantity, composition and shape of the metal object\n• The slice thickness\n• The number of data sampling points
What are some common reactions to iodinated oral contrast agents?
• Transient diarrhea\n• Abdominal pain\n• Flatulence
What are some signs of a Seizure?
• Uncontrollable muscular contractions\n• Facial Twitching\n• Blank facial expression\n• Loss of motor activity\n• Difficulty breathing\n• Confusion
Where can "tube arcing" occur?
• Within the tube\n• Outside of the tube within the oil
What are the two most common orientations for localizer scans?
•AP\n•Lateral
Which studies of the neck call for contrast injection?
•Neck mass\n• Lymph nodes\n• Parathyroid adenoma\n• Parotid gland mass \n• Oral pharynx\n• Larynx\n• Brachial plexus
