MOCK REG CT
Define multiplaner reformation
(MPR) describes the process of displaying CT images in a different orientation from the one used in the original reconstruction process. MPR images may be constructed in the coronal, sagittal, or any other two-dimensional plane. MPR images are typically formed from a vertical stack of contiguous, helically acquired axial CT images.
The average CT value for blood is approximately
+ 45 HU
The image was produced with a 1.0-mm aperture size and was displayed using a 512² matrix and a 15-cm DFOV. The voxel dimension for this image would be:
. 0.29 mm × 0.29 mm × 1.0 mm The pixel dimension may be calculated by dividing the DFOV by the matrix size. This twodimensional pixel size is then multiplied by the length of the voxel
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as:
0.3 mm The minimum object size that a CT scanner can resolve may be calculated by taking the reciprocal value of the scanner's limiting resolution. The reciprocal of 15 lp/cm is 1/15 lp/cm. This is equivalent to 10/15 lp/mm, which equals 0.6 mm/lp. Because a line pair (lp) is equivalent to a line and the space adjacent to it, this value may be divided in half to provide the minimum object that this scanner can resolve: 0.3 mm
A common formula used to calculate dosage of intravenous iodinated contrast material in the pediatric patient is
1 ml per lb or 2ml per kg body weight Dosage calculations for intravenous contrast agent administration in the pediatric patient are usually made following the general rule of 1 mL per pound or 2ml/kg of body weight.
1 rem =
1 rad
Severe reactions to intravenous iodinated contrast material occur in approximately what percent of all patients
1% Severe reactions to intravenous iodinated contrast media occur in less than 1% of all patients. Examples of severe reactions are shock, myocardial infarction, and death
What is the dimension of each pixel in the matrix of an image with the following parameters? FOV = 25.6 cm Matrix = 512 mm x 512 mm
1. 0.5 mm 2. 0.05 cm The dimension of a pixel may be calculated by dividing the field of view (FOV) by the matrix size. The DFOV, 25.6 cm, must first be converted into 256 mm. This is then divided by 512 mm for a pixel dimension of 0.5 mm. Keep in mind that the pixel is a two-dimensional item, square in shape, and the measurement of 0.5 mm corresponds to only one side. The numerical lengths of 0.5 mm and 0.05 cm are equal.
An MDCT image is reconstructed using a 512² matrix and a display field of view of 44 cm. If the detector collimation is set to a section width of 2.5 mm, what is the volume of each voxel?
1. 85 mm3 The linear dimension of the pixel must first be calculated by dividing the DFOV, in mm, by the matrix. This linear pixel dimension is squared to yield the pixel area, in mm². The volume of the voxel may be calculated by multiplying the pixel area by the section width.
What two technical factors exhibits an effect upon longitudinal spatial resolution
1. Detector Pitch 2. Interpolation Algorithm The factors that affect longitudinal spatial resolution and the SSP include the type of spiral interpolation algorithm inherent to the system and the selected detector pitch.
What are two reasons why intravenous contrast is administered during CT evaluation of the pelvis ?
1. Distention and contrast enhancement of the bladder 2. Differentiation of blood vessels and pelvic lymph nodes Intravenous contrast agent administration during a CT examination of the pelvis is valuable for several reasons. The bladder is easily visualized when filled with contrast material, and differentiation between blood vessels and enlarged pelvic lymph nodes is improved. The rectosigmoid junction may be better visualized once opacification has been attained through the use of oral or enema administration of a contrast agent.
What two technical adjustments would decrease the quantum noise of a CT image?
1. Increase mAs 2. Increase section width The quantum noise of a CT image can be reduced by an increase in the number of x-ray photons reaching the detectors. This reduction may be accomplished by increasing mAs or section width (decreased collimation).
What two improvements in CT chest imaging is a direct result of the advent of multi detector CT (MDCT)
1. Reduction in misregistration artifacts 2. increased exam speed Speed is one of the key attributes of helical MDCT. The ability to volumetrically acquire images of the entire chest in a single breathhold has greatly reduced the occurrence of misregistration artifacts. For many applications, MDCT may result in greater patient radiation dose than single-slice CT (SSCT).
What are the two normal stages of the cardiac cycle
1. atrial systole 2. ventricular systole Atrial systole and ventricular systole are normal stages of the cardiac cycle in which the atria and ventricles contract, respectively. Atrial fibrillation is a cardiac arrhythmia that results in an irregular heartbeat
x ray photons are produced by a fast moving electron
1. colliding with an atomic nucleus 2. passing close to an atomic nucleus 3. colliding with an electron within an atom and ejecting it
What corresponds to the period of the cardiac cycle known as ventricular systole
1. contraction of the left and right ventricles
2 examples of moderate adverse reaction to iodinated intravenous contrast media are
1. faintness 2. severe vomiting Examples of moderate or intermediate reactions to iodinated intravenous contrast agents are severe vomiting, dyspnea, faintness, chest pain, and seizures. Shock is an example of a severe reaction.
The purpose of intravenous contrast agent administration during a CT study is to
1. increase the contrast between adjacent structures 2. increase beam attenuation of enhanced structures Iodinated intravenous contrast agents alter the CT image by increasing the density of enhanced structures. Organs, blood vessels, and so on, containing iodine attenuate a greater portion of the primary beam, thereby increasing their attenuation value. This permits greater differentiation of anatomic structures and pathologic processes. Any "enhanced" structure has an increased attenuation value (and subsequent image density) than its normal, unenhanced state.
What are 3 possible side effects that may result form exposing embryo to x ray radiation
1. mental retardation 2. miscarriage 3. deformities
What are 3 advantages of a helical study compared to a conventional, serial CT study
1. minimal anatomical misregistraton sometimes caused by inconsistent breath holding 2. shorter total exam time 3. can retrospectively reconstruct a slice at any arbitrary position
What areas of the head commonly becomes calcified
1. pineal gland 2. choroid plexus The choroid plexus and pineal gland are common areas of calcification in the brain. These areas of increased attenuation and density are easily identified on the CT image.
what would be used in a high resolution study of the temporal bones
1. refused slice thickness 2. reduced reconstruction FOV 3. sharp reconstruction filter
What 3 components of CT image quality may be controlled by the technologist?
1. spatial resolution 2. contrast resolution 3. noise Each component of CT image quality may be affected—either positively or negatively—by the CT technologist. Spatial resolution is affected by geometric factors such as focal spot size and slice thickness. Contrast resolution may be altered by slice thickness, algorithm selection, and noise. The noise level of an image is dependent upon several factors, including patient dose and pixel dimension. Each of these factors must be considered by the CT technologist in an effort to provide high quality CT studies.
Radiation protection of the CT patient should involve which 3 principles
1. strick clinical indication 2. protocol optimization 3. shielding Specific clinical indications ensure that CT is performed only when alternative nonionizing radiation examinations have been deemed inconclusive or inappropriate. An optimized protocol is one that acquires CT images with acceptable levels of noise at the lowest possible dose. Lead shielding should be utilized during CT whenever clinically possible.
Parenteral routes of medication administration include
1. subcutaneous 2. intradermal
What are 2 acceptable forms of immobilization during a CT examination?
1. suspended respiration 2. use of cushioned look and loop (velcro) strap Medical tape is potentially damaging to skin and should not be utilized for immobilization. The patient "breath-hold" is an effective method of reducing motion, particularly during CT examinations of the trunk.
The rights of the patient includes
1. the patient has the right to considerate and respectful care 2. the patient has the right to refuse medical treatment The American Hospital Association drafted A Patient's Bill of Rights in 1973. Included among the 12 "rights" are the patient's right to considerate and respectful care and the right to refuse treatment. Release of the patient's diagnostic examination results is not an inherent right and is at the discretion of the physician(s) involved.
What may occur during the interscan deal of a conventional or serial , CT scan performed on a continuous rotation scanner
1. the table position is incremented 2. the tube continues to rotate in the same direction as during the scan 3. the tube assembly makes a 360 degree rotation
What the 3 parts of the CT Tube
1. tungsten target 2. rotating anode 3. filament the collimator is not part of the ct tube
which of the following section widths would cause the greatest amount of partial volume averaging? a. 1mm b. 3mm c. 5mm d. 10mm
10 mm Large section widths result in long voxel lengths with possibly several tissue types accounted for within the voxel. When a CT number is assigned to the representative pixel, the density of all of the tissue types is averaged, yielding one attenuation coefficient. Narrow section widths tend to decrease the partial volume effect.
there are more than 1 million total pixels in a
1024 x 1024 matrix
The average range for normal prothrombin (PT) time is approximately
12 - 15 seconds Normal prothrombin (PT) times are lab-specific and range between approximately 11 and 15 seconds. This test is used to evaluate the coagulation ability of a patient scheduled to undergo an invasive CT procedure.
The normal range of respiration for an adult is
12 - 20 breathes per minute
During a CTA of the brain's circle of Willis, if an iodinated contrast agent is injected at a rate of 3-4 mL/sec, an adequate delay for optimal vessel opacification would be in the range of:
12 -20 seconds An empiric delay of 12-20 seconds would be adequate to ensure good vessel opacification of the circle of Willis.
If the radiologist requires 2 mm thick contiguous slices through the pituitary, and 2.4 cm of coverage, ________ slices are necessary?
12 slices are necessary
If an image matrix has 360 rows and 360 columns, how many pixels are there in the image?
129,600
The normal platelet count range for an adult is
140,00 - 44000/mLof blood
A solitary pulmonary nodule can be assumed benign when its average density is within
165 - 200 HU Pulmonary nodules appearing on CT examinations of the lungs may be determined as benign if their average density is more than +164 Hounsfield units. Although there have been conflicting studies in this area, researchers tend to agree that density values approaching +200 HU make the benign diagnosis more certain.
List the butterfly needles in decreasing order in terms of bore dimension
19 gauge, 21 gauge, 23 gauge The gauge of a needle signifies its bore dimension or lumen size. The gauge of a needle increases as its lumen size decreases. Therefore, a 19-gauge needle has a larger lumen than a 23-gauge needle.
Assuming a bolus injection of iodinated contrast agent at a rate of at least 4 mL/sec, an appropriate scan delay for a CTA examination of the mesenteric vasculature would be in the range of:
20 - 30 seconds Dual-phase imaging including the arterial phase (20-30 sec) and portal venous phase (60-70 sec) is typically performed for complete evaluation of the mesenteric vasculature. The use of bolus-tracking software or test bolus technique is recommended to ensure appropriate scan timing.
A 64-slice MSCT system employs an array of 64 detectors, each with a dimension of 0.625 mm. What beam collimation is required to expose the middle 32 detectors of the array to transmitted x-radiation?
20mm The selected detector configuration for a given acquisition determines the necessary beam collimation. The selected 32 detectors, each with an individual dimension of 0.625 mm, would require a beam collimation of 20 mm to expose each to transmitted radiation (32 x 0.625 = 20 mm).
Prior to and after contact with each patient, a proper hand-washing technique requires that the technologist use warm soap and water with a circular rubbing motion for at least:
30 seconds Proper hand-washing technique requires a minimum of 30 seconds. The technologist should use warm soap and water with a firm circular motion.
If the slice thickness is changed from 5 mm to 7 mm and all other parameters are held constant, _____% more photons will be used in making the slice.
40
In a modern CT system, the total number of possible Hounsfield values that may be assigned to any one pixel is approximately:
4096 The CT computer system is typically capable of displaying 12 bits of data per pixel and is therefore able to display any of up to 4096 Hounsfield values for each pixel (2¹² = 4096).
During IV contrast agent administration for peripheral CTA examinations, the bolus duration should be equal to the scan time minus:
5 seconds The duration of scan acquisition for peripheral CTA will be based on the anatomic length of the study and the capabilities of the particular CT system in use. Faster scanners run the risk of "outrunning" the bolus by completing the acquisition before the entire contrast volume has been administered. Bolus duration, or the time required to inject a specific volume of contrast, may be calculated as the product of injection flow rate and total contrast agent volume. The subtraction of 5 seconds allows the scanner to maintain pace with the contrast agent as it moves down the aorta and results in the cessation of contrast agent administration just prior (5 sec) to the end of data acquisition.
what would be an example of of noncontiguous images
5.0mm sections reconstructed every 7.5 mm Noncontiguous images are images acquired with an interval greater than the section width. For example, 5.0-mm sections reconstructed every 7.5 mm fail to evaluate the intermittent 2.5 mm of tissue.
The normal range of glomerular filtration rate (GFR) for woman is
60 +/- 10mL/min?m2 Normal range of GFR is 60 +/- 10 mL/min/m²for women and 70 +/- 14 mL/min/m² for men.
The nephrographic phase occurs between n
70 and 90 seconds after the start of injection. Enhancement between renal cortex and medulla reaches equilibrium providing optimal sensitivity for parenchymal lesions
On a third-generation single-row detector scanner, if there are 715 detectors and there are 900 projections in a full rotation, how many samples of attenuation data are collected for the raw data of a single slice if the scan calls for an overscan of a 4000 rotation?
715,000
Patient preparation for a contrast-enhanced CT examination of the chest may include:
Npc for 4 hours prior to the exam The patient should have nothing by mouth (NPO) for several hours prior to a contrastenhanced CT examination of the chest. This practice reduces the incidence of nausea, vomiting, and possible aspiration of contrast material.
Where should the tourniquet be positioned during preparation of a patient for intravenous contrast administration
Proximal to the injection site Prior to the intravenous injection of contrast media, a tourniquet is placed proximal to the injection site. The tourniquet helps distend the vein, making needle insertion easier.
What pathology would most likely require the intravenous injection of an iodinated contrast agent for accurate differential during a CT study of the abdomen
RENAL CYST The diagnosis of simple cyst is accurately made with proper CT examination. Pre- and postcontrast images must be obtained to measure enhancement. The attenuation values for the cystic area should be at or near zero. The diagnoses of angiomyolipoma, renal stone, and diverticulitis can be made without the intravenous injection of contrast material.
Pixel may be defined as
a picture element pixel is an element of the digital image. It is located in a matrix and is a two-dimensional representation of a voxel. When CT numbers are calculated for voxels (volume elements) of tissue, the pixel is assigned the calculated number and a subsequent shade of gray. The pixel may be defined as a picture element, or the smallest component of the digital image.
What type of manipulation involves the use of image data
adjusting the width and level of a window setting The adjustment of the window width or level is a computer manipulation of image data. The image has already been reconstructed from scan or "raw" data. The window changes only the range of pixel values that will be assigned a shade of gray. Adjustments in the algorithm, DFOV, or matrix require the raw data so that the image may be retrospectively reconstructed.
What technical consideration is necessary to differentiate hydronephrosis from parappelvic cysts on CT examination
administration of an iodinated IV contrast agent Parapelvic cysts are simple cysts arising within the renal pelvis. They are similar in appearance to the distention of the pelvis and calyces known as hydronephrosis. Delayed imaging after IV contrast agent administration opacifies the renal pelvis, clearly differentiating hydronephrosis from parapelvic cysts.
what type of pathologic condition cannot be easily diagnosed from a CT scan of the brain
alzheimer's disease Alzheimer's disease is not easily diagnosed from a CT scan of the brain. Alzheimer's disease may present with enlargement of the temporal horns but this is typically not specific on CT examinations.
A patient has a severe vagal reaction to iodinated contrast material that includes bradycardia. Initial treatment may consist of
atropine Patients suffering from vagal reactions to iodinated contrast agents present with hypotension and bradycardia. Treatment includes increasing blood pressure with IV fluids and intravenous administration of atropine to block vagal stimulation of the heart.
The multiple scan average dose (MSAD) is used to describe the
average dose to a single section within a scan of multiple sections The multiple-scan average dose (MSAD) is used to quantify the average cumulative dose to each section within the center of a scan consisting of multiple sections.
A suction unit used on a patient with a chest tube should always remain
below the patient In order for a suction unit to properly drain a chest tube, it must always remain below the level of the patient.
Cupping artifacts most commonly occur in the
brain Cupping artifacts occur when the periphery of an image is much higher in density than the center. This difference in density causes beam hardening to negatively affect the accuracy of the image. The dense bone that surrounds the soft tissue of the brain is a common site for cupping artifacts to occur.
A helical scan performed on a 64 slice MDCT scanner is reconstructed with
cone beam reconstruction
What would absolutely prohibit a patient from undergoing a coronary CTA
contraindication to iodinated contrast agents Contraindication to iodinated contrast agents is the only absolute contraindication to coronary CT, because all such studies must be performed after administration of an iodinated contrast agent.
What term describes the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients
contrast resolution contrast resolution of a CT scanner refers to the system's ability to differentiate objects with similar densities. This ability is also commonly referred to as the low-contrast resolution or the sensitivity of the CT scanner.
A patient is scheduled for an intravenous iodinated contrast-enhanced CT scan of the kidneys. Prior to the injection, the involved medical personnel should examine recently measured laboratory values for
creatine It is important to assess the serum creatinine level of a patient scheduled to undergo a contrast-enhanced CT examination. This is especially true for any patient with a history of renal disease. The serum creatinine level is a laboratory value used to measure renal function and abnormally elevated values are often signs of renal failure.
A test phantom containing water is scanned and five region-of-interest measurements are performed. The subsequent density measurements are compared and demonstrate a maximum deviation of less than 2 HU. This quality assurance test was performed to evaluate the scanner's:
cross field uniformity The test described is used to evaluate the cross-field uniformity of a CT scanner. The ROI measurements are arranged with one at the center of the image and the others rotated about the periphery. Each of the five ROI measurements taken from the water phantom should yield relatively the same CT number value.
A CT number calibration test should be performed
daily
What technical factor adjustments will result in a reduction in patient radiation dose
decrease the miliamperage (mA) Reducing the mAs lowers the overall quantity of x-radiation produced and will in turn reduce the radiation dose to the patient.
Scatter radiation is caused by
deflections form the original trajectory of an x ray photon through the patient
What is capable of causing an edge gradient artifact
dense bone The edge gradient effect occurs at areas of abrupt change in density, which are represented by high spatial frequency signal. The computer may have difficulty interpreting this type of rapidly changing information, and streaks may appear as a result. The interface between dense bone and soft tissue is a common site for the edge gradient effect to occur.
A straight line appearing vertically on the scanogram (pilot) of a fourth generation CT scanner is an artifact most likely caused by
detector malfunction A straight line artifact on a scanogram (pilot) image is most likely caused by a malfunctioning detector in both third- and fourth-generation scanners. As the patient travels through the gantry, the faulty detector does not record any information, leading to the blank line that appears on the image.
The presence of out pocketings in the wall of the colon is referred to as
diverticulosis
The full width at half maximum (FWHM) of a slice sensitivity profile diagram indicates
effective section width is defined as the full width at half maximum (FWHM) of the SSP. It is measured by examining the slice sensitivity profile at half of its maximum height.
CT scanning of the liver for tumor evaluation should not be performed during which phase of contrast enhancement
equilibrium phase Contrast enhancement is at its lowest point during the equilibrium phase. This phase is apparent when the aorta and inferior vena cava differ by less than 10 HU. It is during this phase that hepatic lesions may become isodense with the surrounding hepatic parenchyma. Noncontrast scanning of the liver is actually preferred to scanning during the equilibrium phase.
Infiltration of contrast agent outside of the blood vessel into the surrounding soft tissue is called
extravasation Extravasation, or infiltration of contrast agent into the surrounding tissue, is extremely painful and a potentially serious consequence of improper administration of IV contrast media.
What describes the type of x ray beam used in a third generation CT scanner
fan beam The third-generation CT scanner uses a fan beam projected onto a wide detector array. The third-generation CT x-ray beam is commonly mistaken for the "pencil beam" used with only two detectors in the first-generation CT scanner.
What type of abnormal findings will reduce the density of the liver
fatty infiltrate The density of the liver decreases with the presence of fatty infiltrates. The minimal attenuation of fat and its low CT number cause an overall decrease in the attenuation and CT number of the hepatic parenchyma.
What utilizes convolution
filtered back projection
The human embryo/fetus is most sensitive to radiation in the
first trimester
The lumens of needles used for the injection of contrast media vary in diameter. The unit used to describe this diameter is called
gauge
What term is used to quantify absorbed dose
grays (Gy) absorbed dose describes the amount of x-ray energy absorbed in a unit of mass. It is measured in grays (Gy)
Continuous rotation scanners made what possible?
helical imaging
Areas of a CT image containing abrupt changes in tissue density are electronically represented by
high spatial frequencies The contrast of a CT image is controlled by the spatial frequencies of the tissue(s) within the section. Tissues of differing densities are represented electronically by different spatial frequencies. Adjacent tissues with large differences in density are represented by a high spatial frequency signal.
An abnormal accumulation of fluid around a testicle is termed as
hydrocele
What adjustment in technical factors will result in an increase in spatial resolution
increase in sampling frequency The sampling frequency, or views per rotation (VPM), controls the volume of transmission data acquired for each gantry rotation. Very small objects exhibit high spatial frequencies that only systems with high sampling rates will be capable of resolving.
parenteral contrast administration refers to
intravenous administration The injection of a medication or contrast agent directly into the bloodstream is a type of parenteral administration. Other parenteral routes include intramuscular, subcutaneous, intradermal, and intrathecal.
The most common indication for CT guided radio frequency ablation (RFA) is in treatment of neoplasms involving the
liver The most common indication for CT-guided RFA is in treatment of hepatic neoplasm.
The broadening of the slice sensitivity profile inherent a helical CT acquisition is said to negatively affect the
longitudinal spatial resolution Longitudinal spatial resolution describes the degree to which patient movement during volumetric acquisition can negatively affect image detail.
What is an advantage of automatic CO
lower risk of perforation, insufflation for CT colonography Advantages of automatic CO ₂ insufflation include better overall distention and lower risk of perforation. Also, owing to the faster absorption rate of CO₂, there is a reduction in post-procedural discomfort in the patient.
Increasing Pitch, table increment results in
lowering patient dose
An intrathecal injection of iodinated contrast material may be performed for which CT exam>?>
lumbar spine Intrathecal injections of iodinated contrast material are commonly used in CT myelography of the lumbar spine. This type of injection introduces the contrast agent directly into the subarachnoid space.
The number of electrons that flow form the cathode to the anode in the tube is controlled by the
mA
The spatial resolution of a CT scanner is often measured using the MTF of the system, which is an acronym for
modulation transfer function The modulation transfer function (MTF) is a mathematical method of quantifying the spatial resolution of a CT scanner.
A voxel who's attenuation coefficient is less than that of water is assigned a pixel value with
negative CT number The attenuation coefficient of a tissue describes the tissue's ability to attenuate x-radiation. CT numbers are assigned to pixels based on the basis of the attenuation of the tissue within the voxel. The assignment of a CT number in Hounsfield units arises from a comparison of the attenuation coefficient of the tissue with that of water. Materials with attenuation coefficients less than that of water are assigned negative CT numbers.
The largest deterrent of a CT scanner's contrast resolution is
noise The largest enemy of contrast resolution is noise. Noise appears as a graininess that can obscure the outline and delineation of structures, thus limiting the scanner's ability to separate them.
The CT imaging plane that is parallel to the metatarsals, approximately 20 to 30 degrees caudal from the direct axial plane, is called the
oblique axial plane The oblique axial plane is located parallel to the metatarsals, approximately 20 to 30 degrees caudal from the direct axial plane. MPR images along this plane are used to assess the tarsalmetatarsal joint.
The multiplaner reformation (MPR) images along the long axis of the optic nerve would be best described by which of the following anatomic plane
oblique saggital The optic nerve runs along a lateral-to-medial path from the orbit anteriorly and to the optic chiasma posteriorly. Oblique sagittal MPR images will demonstrate the optic nerve in a profile parallel to its long axis.
What is true regarding the slice thickness of an image reconstructed from a helical scan
on a single row detector scanner, the thickness is equal to the beam collimation
On a multi-row detector scanner, a radiation penumbra may be found
only on the first and last slices of the slice volume
Coronal imaging through the paranasal sinuses is typically performed with the plane of imaging
perpendicular to the hard palate The imaging plane should be positioned perpendicular to the hard palate for coronal evaluation of the paranasal sinuses. This may be achieved by positioning the patient in either the supine, head extended-back position, or with the patient in the prone position. In either case, appropriate angulation of the gantry can help achieve an acquisition angle that is perpendicular to the hard palate. Alternatively, multiplanar reformation (MPR) images may be produced at an angle perpendicular to the axial acquisition, also resulting in coronal images through the paranasal sinuses.
Collimation is accomplished by
physically blocking x rays
The oral administration of barium and iodinated contrast media prior to CT colonography serves the primary purpose of
polyp taggin Dual-agent tagging involves the oral administration of both barium and water-soluble iodinated contrast. The barium tags residual stool and coats the surface of polyps. The iodine contrast tags residual fluid. Tagged fluid and fecal matter exhibit high CT density and appear "white" on the CTC image. Tagging allows for differentiation of polyp from fecal matter and improves the visualization of polyps that may be surrounded by residual fluid.
What Phase of IV contrast agent administration provides the best gastric and intestinal wall enhancement
portal venous For indications involving the GI tract, acquisition is typically obtained during the portal venous phase for optimal gastric and intestinal wall enhancement.
The period of peak hepatic parenchymal enhancement following rapid bolus injection of iodinated contrast is termed the
portal venous phase The portal (or hepatic) venous phase is the period of peak hepatic parenchymal enhancement during which contrast material redistributes from the blood into the extravascular spaces. It occurs at approximately 60-70 seconds after the initiation of rapid bolus contrast administration.
describe the position of the seminal vesicles in the male pelvis
posterior to the bladder and anterior to the rectum
A 25 year old female is scheduled for a CT scan of the sinuses. She is not absolutely certain that she is not pregnant and it has been three weeks since her last menstrual period. Which of the following is the best course of action?
postpone the procedure until she is more certain of her condition
What term describes a view of the anatomical cross-section along the path of the x-ray beam from a single vantage point?
projection
What type of image noise can be most easily reduced by the CT technologist
quantum noise The quantum or statistical noise of a CT image can be reduced by increasing the number of xray photons absorbed by the detectors for each voxel of tissue. This can be accomplished with increases in technique (mAs) and with increases in the pixel and voxel dimensions.
When one is choosing a window to display a CT image, the width defines the
range of CT numbers (pixels) to be displayed The width of a CT window controls the range of pixel values that are assigned a shade of gray. The width is centered on a level that is equal to the value of the tissue of interest.
The pencil thin section of the x ray fan beam that strikes a single detector is called a
ray
What parameter allows adjacent slices to be overlapped without increasing the dose to the patient?
reconstruction intreval
What technical adjustment would result in a decrease in the signal to noise ration (SNR)
reducing the section width Any decrease in the voxel dimension increases noise or decreases the signal-to-noise ratio (SNR).
What refers to the period of the cardiac cycle known as complete cardiac diastole
relaxation of the heart muscle Complete cardiac diastole corresponds to the period of relaxation of the heart muscle. It consists of ventricular and atrial diastole and is indicated by the T wave of an electrocardiogram (ECG).
Glomerular Filtration rate (GFR) is a laboratory assessment test utilized to measure
renal function GFR is an approximation of creatinine clearance and provides an assessment of renal function
The volume of a voxel may be calculated by multiplying the pixel dimension (mm²) by the:
section width As a geometric cuboid, the volume of a voxel may be calculated as the product of the pixel area dimension (mm²) and the section width (mm). The pixel dimension (d) must be first calculated by dividing the display field of view (DFOV) by the matrix size. The area of the pixel may then be found by squaring the value of d (mm). The unit of measurement for voxel volume is mm³.
CT images that have been reconstructed from a portion of the data acquisition process in the hopes of reducing patient motion artifacts are called
segmented images CT images are usually constructed from transmission data acquired during a 360-degree rotation of the x-ray tube. A CT image can also be constructed from a portion of the data acquisition phase. For example, if a patient moves during the last third of a 2-second scan, an image can be constructed from the first 240 degrees of tube rotation, yielding an image free of motion. This process, referred to as segmentation
What unit is used to quantify effective dose
sieverts (Sv) Effective dose approximates the relative risk from exposure to ionizing radiation and is based on the radiosensitivity of a given tissue type. It is measured in sieverts (Sv).
The tortuous S Shaped portion of the internal carotid artery as it enters the bony skull may be referred to as the carotid
siphon refers to the portion of the internal carotid artery as it enters the bony skull and bifurcates into the anterior cerebral and middle cerebral arteries.
The cathode filament helps determine the
size of the focal spot
High-resolution CT examinations of the temporal bones and internal auditory canal should include which of the following technical parameters?
small (less than 10 cm) targeted DFOV CT studies of the temporal bones and internal auditory canal require a high-resolution imaging technique. The tenets of high-resolution CT include thin sections (1-2 mm), a small targeted DFOV, and the use of a high-resolution algorithm (kernel) for reconstruction.CT studies of the temporal bones and internal auditory canal require a high-resolution imaging technique. The tenets of high-resolution CT include thin sections (1-2 mm), a small targeted DFOV, and the use of a high-resolution algorithm (kernel) for reconstruction.
CT acquisition of a water-filled phantom is performed utilizing a standardized set of technical factors. If a region-of-interest (ROI) measurement is made, the image noise corresponds to which of the following data?
standard deviation Noise is most commonly measured by scanning a water-filled phantom with a standardized set of technical factors. The image noise is equal to the standard deviation of pixel values within a region-of-interest (ROI) measurement of the image
The addition of moisture makes an autoclave more efficient at
sterilization than an oven An autoclave is a mechanical device used for sterilization. It involves the use of heat and steam under pressure to eliminate microbes. An oven uses only high heat and is not as efficient as an autoclave.
What patient position is best suited for CT evaluation of the CHEST
supine CT examinations of the chest usually require that the patient be placed in the supine position. Patients may also be scanned in the prone position, to increase aeration of the posterior lung base, or in a lateral decubitus position, to help differentiate certain types of pathology.
The kidneys are usually located anatomically between which vertebrae
t12 and l3 The CT technologist is often called upon to localize the exact area of the kidneys. Although there may be some fluctuation from patient to patient, the kidneys can usually be found between the 12th thoracic vertebrae and 3rd lumbar vertebrae.
The distance that the table travels between slices is called
table increment
Which of the following techniques assists in visualizing the vagina during a CT study of the pelvis?
tampon insertion Insertion of a tampon during the CT examination of the pelvis dilates the vagina and fills it with negative contrast (air). This makes for easier visualization of the vagina and its
what control does the operator have over the x rays in the CT exam
the energy level and the quantity of x rays that can be selected
The process by which electrons are produced at the cathode of a CT x ray tube is known as
thermionic emission When the cathode of an x-ray tube is heated, electrons are released through the process of thermionic emission. It is these electrons that are then accelerated toward the anode for x-ray production.
What is common to both a localizer scan and a conventional serial CT scan
they both produce digital images
x rays are used in CT because
they penetrate the body according to specific attenuation characteristics
Tele radiology is the term used to describe the ability of a PACS to
transmit data from the imaging facility to an off site location
If a calcification with a CT number of +300 appears pure white on an image, which of the following could be the window width and window level selected?
window level = 0, window width = 500
Azimuth setting refers to the relationship between the
x ray tube and the detectors during scout or localizer production. A 0 degree azimuth describes the situation in which the x ray tube and detectors do not rotate but remain above and below the patient, providing a frontal projection
What is used in gas ionization CT detectors
xenon Gases with high atomic numbers, such as xenon, are used in ionization-type CT detector systems. The high atomic number of the xenon gas (Z = 54) increases the incidence of interaction with x-ray photons, thus improving the efficiency of the detector.
In an MSCT system, the detector array is composed of multiple rows of individual detector elements along the
z axis A multislice CT (MSCT) system utilizes a third generation curvilinear detector array with multiple rows of individual detector elements segmented along the longitudinal axis, or z-axis.
Increasing the detector pitch during a spiral CT exam adversely affects the spatial resolution along the
z axis The spatial resolution along the z-axis is decreased when the detector pitch is increased. An increase in detector pitch causes less information to be acquired for each section reconstructed. The section sensitivity profile (SSP) is broadened, and the spatial resolution is reduced.
The articulation between the inferior articular process of one vertebra with the superior articular process of the next is called a
zygapophyseal joint A zygapophyseal joint is the articulation between the inferior articular processes of one vertebra with the superior articular processes of the next. Zygapophyseal joints may also be referred to as facet joints.
