____ generation CT imaging systems were the first designed so that the source and detector arrays
rotated around the patient. No translation was required. - Third
_____ generation CT scanners used a curvilinear detector array and a fan beam. This results in a constant
source-to-detector path len...
CT REGISTRY Revised Questions and Answers /
Guaranteed Pass (excluding anatomy)
_____ generation CT imaging systems were the first designed so that the source and detector arrays
rotated around the patient. No translation was required. - Third
_____ generation CT scanners used a curvilinear detector array and a fan beam. This results in a constant
source-to-detector path length, which is an advantage for good image reconstruction - Third
_____________ a specialized technique which uses narrow section widths and a low-resolution
algorithm for image reconstruction. - High resolution CT
_____________ the window _________________ will make the image appear darker so that bony
structures can be evaluated - increasing & level
_______________ slices can average together a greater variety of tissues and will be more likely to
exhibit this artifact - Thicker
_________________ is commonly caused by faulty detectors. - Ring artifacts
"Fan" beam technology first historically came on the scene with which acquisition geometries? -
Second
"Nutating" is closely associated with which CT geometry - 4th Generation
"Rotate-rotate" applies to which of the following geometries? - Third
1 pound = - 0.45 kilograms
,1 rem= 1 rad - When measuring the radiation dose from x-rays, rads and rems are equivalent. The
units of Sv and rem are used to measure any kind of ionizing radiation where 1 Sv =100rem. The units of
rad and Gy are used to measure specifically x-ray radiation where 1 Gy = 100 rads.
10 rem converted to Sieverts is what? - 0.1 Sv
1st generation ct scanner consists of an x-ray tube & 2 detectors that translate across the patients head
while rotation in 1 degree increments for a total of - 1st generation CT scanners were based on a
translate-rotate principle. The x-ray tube & detectors would translate acroos the patients head and then
rotate 1 degree. This process would repeat in a semicircular fashion, for 180 degrees around the
patient's head
1st Generation scanners - - pencil beam - single detector - the tube/detector assembly moved
across the patient, then rotated by 1 degree - total scan time about 5 min per image - used for head
study - translate-rotate motion
2nd Generation scanners - - fan beam - multiple detectors in a straight line - the tube/detector
assembly moved across the patient, then rotated by 5 degrees - total scan time about 20 secs per image
- translate-rotate motion
3rd Generation scanners - - fan beam - several hundred detectors- curvilinear detector array - 360
degree rotate-rotate motion. Both the x-ray source & the detector array rotate about the same axis.
4th Generation scanners - *fan beam *multiple detectors encircle the patient and do not rotate
around the patient * Only the tube rotates around the patient * Total scan time of 1 second per image or
faster
A bolus injection of iodinated contrast media is administered to a patient scheduled for a CT examination
of the liver, a delay of ________ should be applied - 45 second delay will allow the portal vein to
become completely opacified
A common formula used to calculate dosage of intravenous iodinated material in pediatric patients is -
1 mL per pound
,A complete CT study of the orbits should include - 2.5 x 2.5 mm axial and coronal sections
- narrow sections 1-3 mm are required in both axial and coronal planes to accurately view the orbits
A contrast enhanced CT examination of the chest is completed, when viewing the image it appears small,
making evaluation of the anatomy difficult. To improve image quality which of the following technical
changes may be made? - Decreased DOV---The image was obviously reconstructed in a display
field of view larger than necessary. The image appears small because of this error. The DFOV chosen for
an image should be slightly larger than the diameter of the area of interest.
A CT exam is done with a slice thickness of 10mm, and a 2mm gap is between the slices, the pitch is 1:2
and the total scan time is 5 seconds. What is the table increment for this exam? - *The table
increment is determined by adding the slice thickness with the gap between the slices. 10mm + 2mm =
12mm table increment. The other information given is just that other information to distract you.
A CT examination of the liver shows an abnormal finding of reduced density, which of the following is
most likely the cause? - A fatty infiltrate - they greatly reduce the density of the liver
A CT image is reconstructed using a 512^2 matrix and a display field of view of 17 cm. What is the linear
dimension of each pixel? - 0.3 mm
The dimension of a pixel may be calculated by dividing the field of view by the matrix size. The DFOV of
17 cm must first be converted into 170 mm. This is then divided by 512 mm, for a pixel dimension of 0.33
mm. Keep in mind that the pixel is a two-dimensional item, square in shape, and the measurement of
0.33 mm corresponds to only one side
A CT number calibration test should be performed.. - daily
A CT scan of the pelvis resulted in a dose at the entrance to the patient's skin of 6 rads, the dose at the
center of the patient will be _____ mGy, if it is two-thirds less than the skin dose. - The skin dose
of 6 rads - 4 rads = 2 rads( 1 Gy = 100 rads)
A CT scanner capable of producing an image that is a perfect reproduction of the actual anatomic section
is said to have an MTF modulator transfer function of - 1
, A CT scanner measures the linear attenuation coefficient of a voxel of tissue as 0.4. The linear coefficient
for water in this scanner is 0.2. The CT number assigned to the pixel representing this voxel of tissue is -
First you need to subtract the LAC of a voxel of tissue from the LAC for water
0.2- 0.4 = -0.2
Then you must divide that number by the LAC of water in the scanner
-0.2 divided by 0.2= -1
Then you must multiply this number by a factor of 1000 to yield the value of the pixel in Housfield units
...
answer: -1000
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as - 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/cm, which equals 0.6 mm/lp. Because a line pair (lp) is equivalent to a line and space adjacent to it,
this value may be divided in half to provide the minimum object that this scanner can resolve: 0.3
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 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
A CT study of the brain to visualize MS plaques may be made more sensitive by using ______ delay after
the contrast agent has been injected. - 45 minutes
A CT sudy of the brain to visualize MS plaques may be made more sensitive by using ____ delay after the
contrast agent has been injected. - 45 min.
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