# CT Review- Physics and Instrumentation

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1. Partial volume averaging on the CT image may be decreased by
A. increasing matrix size
B. increasing slice thickness
C. decreasing slice thickness
D. decreasing matrix size
C. decreasing slice thickness
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2. The loss of anatomic information between contiguous sections due to inconsistent patient breathing is called
A. cupping artifact
B. misregistration
C. overshoot artifact
D. out of field artifact
B. misregistration
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3. A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a
A. reformat
B. matrix
C. pixel
D. voxel
B. matrix
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4. What is the dimension of each pixel in an image with a 512x512mm matrix and a DFOV equaling 25.6cm?
A. 0.5mm
B. 0.5cm
C. 0.05cm
D. both a and c
D. both a and c the dimension of a pixel may be calculated by dividing the FOV by the matrix size
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5. The reduction in intensity of an xray beam as it interacts with matter is termed
A. transmission
B. scatter
C. attenuation
D. luminescence
C. attenuation
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6. The major disadvantage of the fan-shaped xray beams used in modern CT units when compared with the pencil-thin beams is
A. increased patient dose
B. excess tube wear
C. increased transmission measurements
D. decreased transmission dose
A. increased patient dose
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7. Which of the following is the most common type of noise found in the CT image?
A. artifactual noise
B. statistical noise
C. electronic noise
D. filter noise
B. statistical noise
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8. Scintillation crystals are used exclusively as detectors in _______CT scanners
A. spiral
B. fourth-generation
C. electron beam
D. third-generation
B. fourth-generation
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9. A first generation CT scanner consists of an xray tube and two detectors that translate across the patient's head while rotating in 1 degree increments for a total of
A. 90
B. 45
C. 360
D. 180
D. 180
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10. Which of the following factors does not affect the dimensions of a voxel?
A. slice thickness
B. kernel
C. matrix-size
D. DFOV
B. kernel the dimension of a voxel is determined by mutiplying the pixel dimension by the slice thickness
(this multiple choice question has been scrambled)
11. Areas of a CT image that contain abrupt changes in tissue density are electronically represented by which of the following?
A. low spatial frequencies
B. high spatial frequencies
C. postitive CT numbers
D. negative CT numbers
B. high spatial frequencies
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12. Which of the following is an analytic form of image reconstruction?
1. iterative technique
2. Fourier reconstruction
3. filtered back-projection
A. 1 and 2 only
B. 1 only
C. 2 and 3 only
D. 1,2, and 3
C. 2 and 3 only
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13. The term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT numbers is
A. linearity
B. quantum noise
C. mottle
D. spatial resolution
A. linearity
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14. The component of the CT scanner responsible for the mathematical calculations of the image reconstruction process is the
A. array processor
B. digital-to-analog converter
C. Data acquisition system (DAS)
D. analog-to-digital converter
A. array processor
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15. Which of the folowing statements regarding retrospective image reconstruction is false?
A. retrospective image reconstruction may be used to adjust the center of the displayed image
B. the slice thickness and the SFOV may be changed
C. scan (raw) data must be available
D. the algorithm, matrix sixe, and DFOV may all be changed
B. the slice thickness and the SFOV may be changed
(this multiple choice question has been scrambled)
16. Which of the following decreases the noise of a CT image?
A. decrease in matrix size
B. decrease in slice thickness
C. increase in matrix size
D. decrease in dose
A. decrease in matrix size
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17. Increasing the pitch during a spiral CT examination adversely affects the spatial resolution along with which of the following?
A. y axis
B. z axis
C. axial plane
D. x axis
B. z axis
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18. When an operator reduces the SFOV for a particular body part, which of the following technical changes occurs?
A. a smaller number of detectors are activated
B. the displayed image appears smaller
C. spatial resolution increases
D. the displayed image appears larger
A. a smaller number of detectors are activated
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19. The mathematical manipulations required during the reconstruction of a CT image are accomplished using a(n)
1. algorithm
2. kernel
3. mathematical filter function
A. 1 and 2 only
B. 1, 2, and 3
C. 1 only
D. 1 and 3 only
B. 1, 2, and 3
(this multiple choice question has been scrambled)
20. Which of the following technical parameters would greatly improve the quality of CT studies requiring multiplanar reformats?
A. contiguous scans with wide section thickness
B. noncontiguous scans
C. overlapping scans with narrow section thickness
D. wide section thickness
C. overlapping scans with narrow section thickness
(this multiple choice question has been scrambled)
21. Which of the following mathematical techniques is used exclusively for image reconstruction with spiral CT scanners?
a. back-projection
c. convolution
c. interpolation
d. iterative techniques
c. interpolation
22. Which of the following reduces scatter radiation reaching the detectors?
A. predetector collimation
B. prepatient collimation
C. both a and c
D. postpatient collimation
C. both a and c
(this multiple choice question has been scrambled)
23. A voxel may be defined as which of the following?
A. the portion of the CRT displaying the image
B. an arrangement of pixels
C. a volume element
D. a miniature image
C. a volume element
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24. Which of the following would increase spatial resolution of a CT examination using the following parameters: large focal spot size, 10mm sections, 512 X 512mm matrix?
1. change to small focal spot size
2. perform 5mm sections
3. reconstruct images in a 320 X 320mm matrix
A. 1, 2, and 3
B. 1 and 3 only
C. 1 only
D. 1 and 2 only
D. 1 and 2 only
(this multiple choice question has been scrambled)
25. A pixel may be defined as
A. a picture element
B. a volume element
C. the portion of the CRT displaying the image
D. a miniature image
A. a picture element
(this multiple choice question has been scrambled)
26. The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as
A. interpolation
B. summation
C. filtering
D. convolution
A. interpolation
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27. When compared with conventional radiography, CT produces diagnostic images with improved
A. patient dose reduction
B. spatial resolution
C. minute detail
D. low contrast resolution
D. low contrast resolution
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28. In 1917, the Austrian mathematician________ proved that it was possible tp reconstruct a three-dimensional object ftom the infinite set of all its projections