Term
The typical range for possible pixel values in a modern CT system is between:
a. -512 HU to +512 HU
b. -1000 HU to +1000 HU
c. -1024 HU to +3071 HU
d. -4096 HU to +4096 |
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Definition
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Term
Which of the following is capable of creating an edge gradient artifact?
a. detector malfunction
b. involuntary patient motion
c. dense bone
d. tube arcing |
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Definition
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Term
The human eye is capable of differentiating approximately _______ shades of gray.
a. 10-25
b. 60-80
c. 100-120
d. 250-256 |
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Definition
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Term
| The ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients |
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Definition
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Term
The Hounsfield value of a pixel is directly related to which of the following?
a. window width
b. field of view size
c. linear attenuation coefficient of water
d. window level |
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Definition
| c. linear attenuation coefficient of water |
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Term
Which of the following is not an iterative method of CT image construction?
a. point-by-point correction
b. Fourier Transform
c. simultaneous reconstruction
d. ray-by-ray correction |
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Definition
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Term
| What is used to quantify effective dose? |
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Definition
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Term
| During HRCT of the lungs, image acquisition upon full expiration may be performed to improve demonstration __________? |
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Definition
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Term
Which of the following sets of reconstruction section widths and intervals would be best suited for a general CT study of the abdomen and pelvis on a patient with a history of lymphoma?
a. 0.625mm x 0.625mm
b. 1.25mm x 2.5mm
c. 5.0mm x 5.0mm
d. 10mm x 15mm |
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Definition
c. 5.0mm x 5.0mm
General CT studies for lymphoma are typically performed contiguously with section widths ranging from 3.0mm to 5.0 mm for routine review.
MDCT might involve thinner detector configuration such as 0.625mm and thicker section widths with thinner images used for MPR or for areas of specific concern. |
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Term
Which of the following sets of section widths and intervals is best suited for a CT examination of the cervical spine to rule out intervertebral disc herniation?
a. 5mm x 5mm
b. 1.25mm x 1.25mm
c. 5mm x 7mm
d. 10mm x 10mm |
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Definition
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Term
| A CT scanner measures the linear attenuation coefficient of a voxel of tissue as 0.40 and the linear attenuation coefficient of water for this scanner is 0.20. The CT number assigned to the pixel representing this voxel of tissue equals: |
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Definition
+1000 HU
CT number of a pixel is calculated by subtracting the linear attenuation coefficient of water from the linear attenuation coefficient of the tissue within the voxel. This number is then divided by the linear attenuation coefficient of water and multiplied by a contrast factor of 1000 to yield the value of the pixel in Hounsfield units. |
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Term
Which of the following technical factors exhibits an effect upon longitudinal spatial resolution?
(1) detector pitch
(2) interpolation algorithm
(3) display field of view (DFOV)
(these also affect the SSP) |
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Definition
1 and 2 only
The type of spiral interpolation algorithm inherent to the system and the selected detector pitch |
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Term
Which of the following technologic advances has led to the development of spiral/helical CT scanning?
(1) slip ring technology
(2) electron beam technology
(3) high efficiency xray tubes |
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Definition
1 & 3 only
The advents of slip ring technology and improvements in xray tube design have made spiral and helical CT scanners possible.
Slip rings have taken the place of the cumbersome cables used previously to transmit the CT signal and power supply to the tube and detectors. |
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Term
After initiation of rapid bolus administration of an iodinated contrast agent, the corticomedullary phase of renal contrast enhancement occurs at approximately:
a. 20-25second
b. 30-40 seconds
c. 70-90 seconds
d. 3-5 minutes |
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Definition
b. 30-40 seconds
The Corticomedullary phase is a late arterial phase beginning 30-40 seconds after the initiation of contrast agent administration. Optimal enhancement of the renal cortex and renal veins occurs during this period |
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Term
The water soluble oral contrast agents used for CT scans of the abdomen and pelvis should contain approximately ______ iodine.
a. 2%-5%
b. 8%-12%
c. 15%-20%
d. 25%-40% |
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Definition
2%-5%
A solution of 2%-5% iodinated water soluble contrast agent and water provides a sufficient bowel opacification for CT studies of the abdomen and pelvis. Some instituitions may use a flavored contrast agent or add a flavoring agent to the solution for ease of consumption. Common water soluble contrast media include Gastrografin and Hypaque. |
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Term
Which of the following types of image noise can be most easily reduced by the CT technologist?
a. electronic noise
b. artifactual noise
c. quantum noise
d. detector noise |
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Definition
c. quantum noise
this can be reduced by increasing the numbers 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 ans voxel dimensions. |
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Term
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?
a. 10 mm
b. 20 mm
c. 32 mm
d. 64 mm |
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Definition
b. 20 mm
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). |
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Term
The volume of a voxel may be calculate by multiplying the pixel dimension (mm^2) by the:
a. display field of view (DFOV)
b. section width
c. pitch
d. scan field of view (SFOV) |
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Definition
b. section width
As a geometric cuboid, the volume of a voxel may be calculated as the product of the pixel area dimension (mm^2) 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 mm^3. |
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Term
A high-osmolar contrast material has an average osmolality of:
a. 100-300 mOsm/kg water
b. 600-850 mOsm/kg water
c. 1000-2400 mOsm/kg water
d. 4000-7000 mOsm/kg water |
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Definition
| c. 1000-2400 mOsm/kg water. |
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Term
The full width at half maximum (FWHM)of a slice sensitivity profile diagram indicates the:
a. limiting resolution
b. signal-to-noise ratio (SNR)
c. dose profile
d. effective section width |
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Definition
d. effective section width
effective section width is defined at the full width at half maximum of the SSP. it is measured by examining the slice sensivity profile at half of his maximum height. |
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Term
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:
a. partial volume averaging
b. noise
c. detector drift
d. beam hardening |
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Definition
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Term
A CT image of a homogeneous material contains variations in CT number from pixel to pixel. This image is said to have:
a. high contrast
b. sensitivity
c. definition
d. noise |
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Definition
d. Noise
A CT image of a homogeneous material should have pixels with the same CT number. Any variation in CT number between pixels indicates that noise has entered the system, causing a loss in accuracy. |
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Term
Which of the following technical adjustments would decrease the quantum noise of a CT image?
(1) increase mAs
(2) decrease section width
(3) increase section width |
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Definition
1 & 3 only
Quantum noise of a CT image can be reduced by an increase in the number of xray photons reaching the detectors. This reduction may be accomplished by increasing mAs or section width (decreased collimation) |
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Term
Quantitative computed tomography (QCT) is a specialized technique used most often for the diagnosis of:
a. lymphoma
b. osteroporosis
c. renal cyst
d. hemangioma |
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Definition
b. osteoporosis
QCT is used to measure the mineral content of a bone. Density measurements of the patients bone are compared with density measurements of a reference phantom. The bone mineral density (BMD) values are compared with normal values to assess osteoporosis. |
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Term
As related to the cardiac cycle, the term ______ refers to the contraction of the heart muscle.
a. diastole
b. equilibrium
c. systole
d. a-fib |
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Definition
c. systole
the term systole refers to the contraction of heart muscle. it can be divided between atrial systole and ventricular systole |
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Term
During a CT examination of the abdomen including intravenous administration of an iodinated contrast agent, which of the following abnormal findings could appear hyperdense in comparison with surrounding tissue?
a. angiomyolipoma of the kidney
b. simple hepatic cyst
c. dilated common bile duct
d. gallstone |
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Definition
d. gallstone
gallstones appear hyperdense in comparison with the bile filled gallbladder. Some gallstones having lower attenuation values can appear isodense on a CT scan of the abdomen. |
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Term
The kidneys are usually located anatomically between which vertebrae?
a. T6 and L2
b. T12 and L3
c. L2 and L4
d. L3 and S1 |
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Definition
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Term
The largest deterrent of a CT scanner's contrast resolution is:
a. patient motion
b. noise
c. hardware malfunction
d. beam hardening |
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Definition
b. 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. |
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Term
After initiation of rapid bolus administration of an iodinated contrast agent, the hepatic (portal) venous phase of contrast enhancement occurs at approximately:
a. 15-20 seconds
b. 25-35 seconds
c. 60-70 seconds
d. 120-180 seconds |
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Definition
c. 60-70 seconds
hepatic or portal 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 administration of contrast agent. |
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Term
What is the longitudinal axis?
a. x axis
b. y axis
c. z axis
d. entire circumference of the gantry |
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Definition
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Term
Increasing the detector pitch during a spiral CT exam adversely affects the spatial resolution along which of the following?
a. axial plane
b. x axis
c. y axis
d. z axis |
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Definition
d. z axis
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. |
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Term
Which of the following technical changes may increase the partial volume effect present on a spiral CT scan?
a. decrease in pitch
b. decrease in section width
c. increase in matrix size
d. increase in pitch |
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Definition
d. increase in pitch
When the pitch is increased during a spiral CT scan, either the section width or the table speed has been increased. The effects of increased section width on the partial volume effects are obvious. the increased table speed also plays a role in increasing partial volume averaging. Because the table moves through the gantry at a faster rate, each rotation of the tube and detectors is responsible for recording more information. This causes a broadening of the section sensitivity profile (ssp), which manifests as partial volume averaging. |
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Term
Which of the following technical factor(s) play(s) a role in the production of an isotropic dataset?
(1) section width
(2) scan field of view (SFOV)
(3) display field of view (DFOV) |
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Definition
1 & 3 only
Isotropic resolution is approached by choosing the thinnest detector collimation available to produce the thinnest slices available and by reconstructing the acquired data with the smallest DFOV allowed according to the part of interest. Minimizing these 2 factors results in voxsels approaching equal lengths in all directions. |
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Term
During CT angiography, images may be reconstructed using only the greatest density encountered along each ray. This type of specialized CT image is called a(n):
a. 3D model
b. volume rendered image
c. MIP image
d. surface rendered image |
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Definition
c. MIP image
Maximum intensity projections (MIPs) are commonly used during specialized studies such as CT angiography.
An MIP image is constructed by displaying only the maximum intensity pixel found along each ray. Remember that a ray is the path from the focal spot of the xray tube to the detector. This technique is valuble in displaying contrast enhanced blood vessels that are surrounded by various types of tissue. |
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Term
Ischemic brain tissue is identified as an infarct core when cerebral blood volume (CBV) falls below:
a. 2.5 ml/100 g
b. 5.0 ml/100 g
c. 10.0 ml/100 g
d. 50.0 ml/100 g |
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Definition
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Term
When one is choosing a window to display a CT image, the width defines:
a. midpoint of the range of pixels displayed
b. range of CT numbers (pixels) to be displayed
c. range of pixel values included in the ROI
d. average CT number of the tissue of interest |
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Definition
b. 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. |
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Term
A suction unit used on a patient with a chest tube shoulder always remain:
a. below the patient
b. level with the patient
c. above the patient
d. at the head of the patient's bed |
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Definition
a. 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 |
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Term
After initiation of rapid bolus administration of an iodinated contrast agent, the excretory phase of renal enhancement occurs at approximately:
a. 20-25 seconds
b. 30-40 seconds
c. 70-90 seconds
d. 3-5 minutes |
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Definition
d. 3-5 minutes
the excretory phase is a delayed imaging phase that begins approximately 3 minutes after the initiation of contrast administration. during this phase, contrast material has been excreted into the renal calyces, opacifying the renal pelvis and the remainder of the urinary collecting system (ureters, bladder). the excretory phase best demonstrates the filling defects and potential lesions involving the urothelium such as those from transitional cell carcinoma (TCC) |
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