CT Procedures Unit 1
What is the common matrix size in computed tomography?
512x512
Define the term osmolality.
# of particles in solution, per unit liquid compared to that of blood
Identify characteristics for the 1s t - 4th generations of computed tomography scanners:
1st Generation - Pencil beam, 1 degree increments, could only do heads, translate rotate, 1 detectors, 2nd Generation - 10 degree increments, rotate rotate, bowtie filter, more detectors. 3rd Generation - 360 degrees, rotate rotate, paved the way for the modern CT, ring artifact, more detectors, cables could get wound up. 4th Generation - Rotate only, motion artifact, fixed detectors
What is the correct dose calculation for IV contrast media when administering the dosage to a pediatric patient?
2 ml/kg or 2 mililiter per kilogram
State the position of the x-ray tube on both the AP and Lateral localizer scanogram
AP is above the patient, Lateral is to the side of the patient
Name the radiation protection considerations a technologist should perform to reduce patient dose in computed tomography.
Adhering to ALARA, shielding, correct centering, communication
Identify information that must be documented when using IV contrast.
Allergies, kidney disease or failure, any types of cancer, diabetic, drug use, have asthma, pts history, adverse effects, treatments
Explain the difference of a patient suffering from anaphylactic shock and contrast induced nephrotoxiciy.
Anaphylactic shock- Allergic reaction immediately after contrast administration; Nephrotoxicity- serious delayed effect of contrast reduces renal function
What is it called when an unwanted streak occurs on a CT image due to metal objects, contrast media or incorrect positioning of the patient?
Artifact
Explain the difference between the following scanning terms: Scanogram, Axial, Helical
Axial CT Scan: During this method the patient moves to the desired position and remains stationary while the tube rotates around the patient, then moves again. Has an interscan delay Scanogram (Localizer) CT Scan: Obtained when the tube is stationary and the patient moves through the scanner Helical (Spiral) CT Scan: Scanning method that involves continuous tube rotation, x-ray output, and movement of the patient
Identify the image planes in which computed tomography images can be produced.
Axial, Coronal, Sagittal
Why is the 1st and 2nd generation scanners known as the "Translate Generations"?
Because only the tube moved
What does a GFR calculate and what factors are utilized in the calculating this lab value?
Blood creatinine levels- based on age, body size & gender. Calculates kidney function
Define the purpose of the following detector efficiencies: Capture, absorption and conversion efficiency
Capture efficiency: How well the detectors receive photons from the patient. Depends on detector size and distance between detectors Absorption efficiency: How well the detectors convert incoming x-ray photons. Depends on tube material used and thickness of detectors Conversion efficiency: How well the detector converts the absorbed photon info to a digital signal for the computer.
Identify the risk factors for contrast induced nephrotoxicity (CIN).
Caused by the delayed reaction to contrast media, Diabetes, Myeloma, Advanced Age, CV disease
List the four basic steps the computer system performs in computed tomography.
Controls the Data acquisition, Image reconstruction, Storage of image data, Image display
Explain the responsibilities of the following CT system components: detectors, operators console, gantry, aperture, table
Detectors: CT element that collects attenuation information Operators Console: Where the exam is controlled and imaging parameters can be changed Gantry: Ring shaped part of the CT scanner that houses many of the components necessary for the system Aperature: The opening to the gantry Table: Moves the patient in and out of the gantry. Cannot be over worked
What equipment is characterized as the 5th generation CT Scanner?
Electron Beam Computed Tomography (EBCT)- Cardiac imaging
Describe the medications used to reduce or eliminate allergic effects.
Epinephrine, Benadryl, Allegra, Diphenhydramine, Lidocaine
If a patient ingests a significant amount of protein in their daily diet how will this affect their overall creatinine levels?
Goes up. BUN- amount of nitrogen in body in the form of urea Creatinine- Kidney filtering- can be serum or urine
What is a normal range of GFR for an average healthy adult?
Greater than 90
List the three most common methods of administering contrast media for CT procedures
Hand injection, power injector, and oral
Why is tungsten used for the CT anode tube?
Has a high melting point
What is the best prevention measures a technologist to reduce a patient's likelihood of having CIN reaction when water-soluble iodinated contrast media is administered?
Having the pt hydrated
Name three osmolality iodinated contrast agents used in CT.
High osmolality-may have as much as 7 times the osmolality of blood (Does not flow well with blood) agents, low osmolality agents, isomolar agents
Explain detector dose efficiency and the three factors in which it is composed.
How efficient the detector is at capturing an x-ray and is controlled by capture efficiency, absorption efficiency, and conversion efficiency
Define computed tomography and the individual whom was awarded the Nobel Prize for the invention
Imaging modality that can produce a cross sectional tomographic plane of any part of the body- Cormick and Hounsfield
Why is a power injector preferred for administering contrast media for CT procedure especially in bolus form?
It is more precise and can control rate of flow
Identify the difference between the barium sulfate used in conventional radiography to the barium sulfate mixture (Ready CAT) for computer tomography exams
It must be diluted because it tends to settle after injection and it will cause a beam hardening artifact
Understand the patient's exam prep before having a CAT scan. (IV and Oral Contrast Media)
Labs to be done, NPO 4 hours prior (for digestive studies pt needs to be NPO 12 hours prior for oral)
Define the term extravasation.
Leakage of a vessel into a tissue
Define Hounsfield Scale also identify the number used to identify the following elements: Water Bone & Air
Measure of beam attenuation capability of a specific structure. Water: 0 Bone: 1000 Air: -1000
State the four functions of the data acquisition system.
Measurement of transmitted beam, encoding measurements into binary data, logarithmic conversion of data, digital data transmission to the computer
When reviewing a patient' BUN and Creatinine lab levels, what medical information about the patient would these values indicate for the administration of intravenous contrast media?
Must make sure the patients BUN and Creatinine are within normal range to give the desired amount. If it's not in the range you cannot administer the contrast. But if the benefit outweighs the risk... make sure radiologist is consulted
What happens to a person's GFR value as they age?
Naturally deteriorates
Define the following computer tomography terminology: Pixel, Voxel, Matrix
Pixel: Picture element- 2D square element Voxel: 3D picture element Matrix: Rows and columns of pixels
Describe the purpose of the "bow tie" filter used in computed tomography
Provides a more uniform beam intensity
Describe the importance slip ring technology had on helical or spiral imaging
Provides continuous scanning power to the x-ray system
Explain the difference between reconstructing and reformatting an image in computed tomography.
Reconstruction- Images that are digitized using an algorithm in which the image was already received by computer , uses raw data (puts filter on the image-lung window) Reformatting- Uses image data to generate images in a plane or orientation different from the original image
List contraindications for iodinated contrast media.
Same as for conventional radiography, metallic taste and warm sensation
Why should barium sulfate not be used for a patient that is suffering a bowel obstruction? What type of contrast media should be used instead?
Since barium can harden if it does not move, it can cause even more of an obstruction. Water soluble contrast should be used
Why is sickle cell anemia patients a concern when a technologist is to administer IV contrast media for their CT examination?
They could get blood clots
Explain why the tube and detector alignment is so critical in computed tomography.
This is required to avoid degraded images. You will loose information
How would a technologist adhere to ALARA when performing a CT procedure?
Using the best technical factors to optimize image quality and minimize pt. dose
Explain the difference between window level and window width.
Window level- Selects the center value of the window width (overall density lightness/darkness). Window width- Determines the quantity of Hounsfield units represented as shades of gray
