CT Image Quality 3
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? 1. Window level = 0, window width = 500 2. Window level = + or - 300, window width = 500 3. Window level = +100, window width = 1000 A. 1 only B. 2 only C. 3 only D. 2 & 3
A. 1 only
Which of the following values for pitch would stretch the x-ray helix the most? A. 1.5 B. 1.0 C. 0.8 D. 0.5
A. 1.5
The ________ determines how penetrating the x-ray beam will be. A. kVp B. rotation time C. mA D. pitch
A. kVp
Compared to a CT scan protocol without iterative reconstruction applied, when using iterative reconstruction the scan parameter most likely to be reduced is: A. mAs B. matrix C. pitch D. scan field-of-view
A. mAs
________ affects the CT number of water. A. No imaging parameter B. the slice thickness C. the kVp D. THe mAs
A. no imaging parameter
On MDCT, the final reconstructed slice thickness is determined by the: A. number of rows of detectors and the size of the detectors whose attenuation data gets combined B. pitch C. reconstruction interval D. collimation of the x-ray beam
A. number of rows of detectors and the size of the detectors whose attenuation data gets combined
Which of the following parameters allows adjacent slices to be overlapped without increasing the dose to the patient? A. reconstruction interval B. slice thickness C. table increment D. pitch
A. reconstruction interval
The distance that the table travels between slices is called: A. table increment B. collimation C. rotation D. reconstruction interval
A. table increment
The ability to scan a moving organ without seeing motion artifacts on the images is an example of an exam performed with high: A. temporal resolution B. spatial resolution C. contrast resolution D. noise
A. temporal resolution
Which of the following is not directly proportional to MAs? A. the mean energy of the x-ray photons leaving the tube B. The number of x-ray photons leaving the x-ray tube C. X-rays tube heating D. dose to the patient
A. the mean energy of the x-ray photons leaving the tube
If a reconstruction FOV of 32 cm and a 512 x 512 matrix are used, the pixel size is __________ mm. A. 0.35 x 0.35 B. 0.625 x 0.625 C. 1.6 x 1.6 D. 3.25 x 3.25
B. 0.625 x 0.625
Which of the following can be changed retrospectively? 1. The slice thickness from an MDCT helical scan 2. The slice overlap from a single-row detector scanner helical scan 3. The slice thickness from a single-row detector scanner helical scan A. 1 only B. 1 & 2 C. 2 & 3 D. 1, 2, & 3
B. 1 & 2
Which of the following does not occur when reconstruction FOV is decreased? 1. Spatial resolution is increased 2. Pixel size is increased 3. Noise in the image increases A. 1 only B. 2 only C. 3 only D. 1, 2, & 3
B. 2 only
Which of the following will result in an increased voxel size? 1. Decreased reconstruction FOV 2. Increased slice thickness 3. Increased matrix A. 1 only B. 2 only C. 2 & 3 D. 1, 2, & 3
B. 2 only
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. A. 30 B. 40 C. 60 D. 80
B. 40
CT numbers ___________ would appear black if a window width of 400 and a window level of -100 are used. A. above +200 B. below -300 C. below -200 D. above +100
B. below -300
Which of the following parameters causes helical slices to be reconstructed so they overlap? A. table increment B. reconstruction interval C. pitch D. collimation
B. reconstruction interval
Which of the following is a reason to increase the pitch? 1. A greater volume of anatomy can be covered in a given time 2. A given volume of anatomy can be covered faster 3. Radiation dose to the patient can be increased A. 1 only B. 2 only C. 1 & 2 D. 2 & 3
C. 1 & 2
If the radiologist requires 2 mm thick contiguous slices through the pituitary, and 2.4 cm of coverage, __________ slices are necessary. A. 8 B. 10 C. 12 D. 13
C. 12
Which of the following is false about the spatial resolution of an image? 1. Resolution is independent on matrix size 2. Resolution is dependent on reconstruction FOV 3. Resolution is dependent on scanned FOV A. 1 only B. 2 only C. 3 only D. 1, 2, 3
C. 3 only
On a conventional, or serial, CT scan, if we want 5 mm slices with 1 mm of overlap, the table increment should be ______ mm. A. 1 B. 3 C. 4 D. 5
C. 4
Which of the following has the highest patient dose assuming all other parameters are the same? A. mA =200, rotation time=2 seconds B. mA =200, rotation time=1 second C. mA =150, rotation time=3 seconds D. mA =400, rotation time=1 second
C. mA =150, rotation time=3 seconds
There are _________ total pixels in a 1024 x 1024 matrix. A. 2048 B. 524,288 C. more than 1 million D. more than 2 million
C. more than 1 million
Which of the following determinants of CT image quality is responsible for how grainy or speckled a CT image appears? A. resolution B. linearity C. noise D. contrast
C. noise
Which of the following parameters is responsible for partial volume averaging? A. matrix size B. kVp C. slice thickness D. patient dose
C. slice thickness
A set of images is reconstructed with a 150 mm reconstruction FOV. Keeping all other parameters constant, a second set of images is reconstructed with a 300 mm reconstruction FOV, and then magnified so that the anatomical structures in the first and second set appear the same size. Which of the following statements is false? 1. The resolution of the second set of images is better than the first set 2. The apparent noise in the second set of images is more pronounced than the first set 3. The patient dose of the first set of images is higher than the second set A. 1 & 2 B. 1 & 3 C. 2 & 3 D. 1, 2, & 3
D. 1, 2, & 3
An increase in ____________ will result in hardening of an x-ray beam. 1. Tissue density 2. tissue thickness 3. kVp A. 1 only B. 2 only C. 3 only D. 1, 2, & 3
D. 1, 2, & 3
Which of the following statements is false? 1. Magnification requires the raw data 2. Increasing magnification increases resolution 3. Magnification decreases the size of displayed anatomy A. 1 only B. 2 only C. 3 only D. 1, 2, & 3
D. 1, 2, & 3
Which of the following would be used in a high resolution study of the temporal bones? 1. Reduced slice thickness 2. Reduced reconstruction FOV 3. Sharp reconstruction filter A. 1 only B. 2 only C. 3 only D. 1, 2, & 3
D. 1, 2, & 3
A CT Number Calibration Test should be performed: A. weekly B. annually C. monthly D. daily
D. daily
________ the window ________ will make the image appear darker so that bony structures can be evaluated. A. increasing, width B. decreasing, level C. decreasing, width D. increasing, level
D. increasing, level
Which of the following is the expected result of a CT number calibration test performed on a water phantom? A. 0 + or - 3 B. 0 + or - 5 C. 100 + or - 3 D. 1000 + or - 5
A. 0 + or - 3
The smallest object that can be resolved if a reconstruction FOV of 24 cm and a 512 x 512 matrix are used is ________ mm. A. 0.47 B. 1.00 C. 2.13 D. 3.57
A. 0.47
Which of the following are possible results of partial voluming? 1. Decreased sharpness of edges 2. Misleading CT numbers 3. Improvement in resolution A. 1 only B. 2 only C. 1 & 2 D. 1, 2, & 3
C. 1 & 2
Increasing _________ results in lowering the patient dose. 1. Pitch 2. mAs 3. Table increment A. 1 only B. 1 & 2 C. 1 & 3 D. 1, 2, & 3
C. 1 & 3
Which of the following is the conversion equation from CT number to Hounsfield unit? A. CT number = 0.5 x Hounsfield unit B. CT number = (Hounsfield unit)2 C. CT number = Hounsfield unit D. CT number = 2 x Hounsfield unit
C. Ct number = Hounsfield unit
If a thin slice is used, which of the following would help reduce the apparent image noise? A. reduced reconstruction field of view B. increased matrix C. increased mAs D. increased kVp
C. increased mAs
Which of the following parameters affects the contrast of a CT image? A. reconstruction interval B. mAs C. kVp D. CT number
C. kVp
For a given distance of coverage, which of the following is true? 1. As reconstruction FOV increases, patient dose increases 2. As pitch increases, patient dose decreases 3. As slice thickness increases, patient dose decreases A. 1 only B. 2 only C. 3 only D. 2 & 3
D. 2 & 3
Which of the following would be used to better visualize low contrast resolution? 1. Decreased mAs 2. Sharp reconstruction filter 3. Narrow window width A. 1 only B. 2 only C. 1 & 2 D. 3 only
D. 3 only