practice CT method test

1. The major disadvantage of the fan shaped x-ray beams used in modern CT units when compared with "pencil thin" beams is:
A. Increased transmission measurements
B. Increased patient dose
C. Decreased transmission measurements
D. Excess tube wear

increased patient dose

2. Which of the following decreases the noise of the CT image?
A. Decrease in dose
B. Decrease in lice thickness
C. Increase in matrix size
D. Decrease in matrix size

Decrease in matrix size

3. Quality control measurements to test the accuracy of the calibration of the CT scanner should be performed?
A. Daily
B. Weekly
C. Monthly
D. Annually


4. Pixels representing tissues with average attenuation coefficients greater than that of water have which of the following types of values?
A. Extremely small
B. Positive
C. Negative
D. None of the above


5. What is the dimension of each pixel in an image with 512 x 512mm matrix and a DFOV equaling 25.6?
A. 0.5 mm
B. 0.5 cm
C. 0.05 cm
D. Both A and C

Both A and C

6. Which of the following statements regarding prepatient collimation is true?1. An increase in prepatient collimation increases Pt dose.2. Prepatient collimation is used to focus radiation through the section of interest.3. Prepatient collimation directl

3 only

7. Which of the following is the most common type of noise found in the CT image?
A. Statistical noise
B. Electronic noise
C. Artifactual noise
D. Filter noise

statistical noise

8. The fluctuation of CT numbers in an image of uniform, homogeneous material is known as:
A. Linearity
B. Noise
C. Artifact
D. Partial volume effect


9. Which of the following statements is correct regarding the radiographic film used to archive CT images?1. it is a double-emulsion film2. it is sensitive to UV light only3. it may be used in conjunction with a multiformat or laser camera
A. 1 only
B. 2

3 only

10. Which of the following is not commonly used as a CT scintillation detector material?
A. Ceramic rare earth
B. Silver halide
C. Bismuth germinate
D. Cadmium tungstate

silver halide

11. In the binary number system, a byte is a series of ___________ bits of information.
A. 2
B. 4
C. 8
D. 16


12. Areas of a CT image that contain minimal changes in tissue density are elctronically represented by:
A. Positive CT numbers
B. High spatial frequencies
C. Negative CT numbers
D. Low spatial frequencies

low spatial frequencies

13. The process by which electrons are produced at the cathode of a CT x-ray tube is known as:
A. Rectification
B. Anode heel effect
C. Thermionic emission
D. Isotropic emission

Thermionic emission

14. Which of the following is the best method to reduce respiratory motion on the CT image?
A. Good patient - technologist communication
B. Reduced scan times
C. Use of immobilization devices
D. Glucagon administration

Good patient - technologist communication

15. When compared with conventional radiography, CT produces diagnostic images with improved:
A. Low-contrast resolution
B. Spatial resolution
C. Minute detail
D. Patient dose reduction

low contrast resolution

16. The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as:
A. Filtering
B. Interpolation
C. Convolution
D. Summation


17. Which of the following would increase spatial resolution of a CT examination using the following parameters: large focal spot size, 10 mm sections, 512 x 512 mm matrix.1. Change to small focal spot size2. Perform 5 mm sections3. Reconstruct images in

1 and 2 only

18. Which of the following technical parameters would greatly improve the quality of CT studies requiring multiplanar reformats?
A. Noncontiguous scans
B. Wide section thicknesses
C. Contiguous cans with wide section thickness
D. Overlapping scans with na

Overlapping scans with narrow section thickness

19. The term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT numbers is:
A. Linearity
B. Mottle
C. Quantum noise
D. Spatial resolution


20. In 1917, the Austrian mathematician _____________________ proved that it was possible to reconstruct a three dimensional object from the infinite set of all of its projections.
A. Radon
B. Tsien
C. Bracewell
D. Cormack


21. A voxel may be defined as which of the following?
A. The portion of the CRT displaying the image
B. A miniature image
C. A volume element
D. An arrangement of pixels

A volume element

22. Which of the following may be used for the archival storage of CT images?1. magnetic tape2. VHS tape3. magnetic optical disk
A. 1 only
B. 1 and 3
C. 2 and 3
D. 1,2, and 3

1 and 3

23. A first generation CT Scanner consists of an x-ray tube and two detectors that translate across the patients's head while rotating in 1 degree increments for a total of:
A. 45 degrees
B. 90 degrees
C. 180 degrees
D. 360 degrees

180 degree

24. The portion of the primary beam interacting with a single detector is known as a:
A. Ray
B. View
C. Profile
D. Sample


25. The term "beam hardening describes which of the following physical phenomena?
A. The decrease in average photon energy of a heterogeneous x-ray beam
B. The increase in average photon energy of a homogeneous x-ray beam
C. The increase in average photon

The increase in average photon energy of a heterogeneous x-ray beam

26. Which of the following is the primary interaction between x-ray photons and tissue during CT examinations?
A. Bremsstrahlung effect
B. Characteristic effect
C. Compton effect
D. Coherent scatter

compton effect

27. Scintillation crystals are used exclusively as detectors in __________________ CT scanners?
A. Electron beam
B. Third-generation
C. Fourth generation
D. spiral

Fourth generation

28. Which of the following mathematical techniques is used exclusively for image reconstruction with spiral CT scanners?
A. Convolution
B. Interpolation
C. Iterative techniques
D. Back-projection


29. A straight line appearing vertically on the scanogram (pilot) of a fourth-generation CT scanner is an artefact most likely caused by:
A. Edge gradient
B. Detector malfunction
C. Tube arcing
D. Beam hardening

Detector malfunction

30. The loss of anatomic information between contiguous sections due to inconsistent patient breathing is called:
A. Cupping artifact
B. Misregistration
C. Over
D. Out of field artifact


31. A pixel may be defined as:
A. athe portion of the CRT displaying the image
B. A volume element
C. A picture element
D. A miniature image

A picture element

32. When an operator reduces the SFOV for a particular body part, which of the following technical changes occurs?
A. The displayed image appears larger
B. Spatial resolution increases
C. A smaller number of detectors are activated.
D. The displayed image

a smaller number of detectors are activated

33. Which of the following factors doesnot affect the dimensions of a voxel?
A. Slice thickness
B. Matrix size
C. Kernel


34. Which of the following reduces scatter radiation reaching the detectors?
A. Postpatient collimation
B. Prepatient collimation
C. Predetector collimation
D. Both A and C

Both A and C

35. First generation CT scanners used a method of data acquisition based on a _______________ principle.
A. Multiplanar
B. Rotation only
C. Translate - rotate
D. Transaxial

Translate - rotate

36. Partial volume averaging on the CT image may be decreased by:
A. Increasing matrix size
B. Decreasing matrix size
C. Increasing slice thickness
D. Decreasing slice thickness

decreasing slice thickness

37. Increasing the pitch during a spiral CT examination adversely affects the spatial resolution along with which of the following?
A. Axial plane
B. X axis
C. Y axis
D. Z axis

Z axis

38. The mathematical manipulations required during the reconstruction of a CT image are accomplished using a(n):1. algorithm2. kernel3. mathematical filter function
A. 1 only
B. 1 and 2 only
C. 1 and 3 only
D. 1,2, and 3

1,2,and 3

39. The reduction in intensity of an x-ray beam as it interacts with matter is termed:
A. Scatter
B. Attenuation
C. Transmission
D. Luminescence


40. An average CT number value for blood is:
A. -20 Hounsfield units
B. +10 Hounsfield units
C. +45 Hounsfield units
D. +100 Hounsfield units

+45 hounsfield units

41. Areas of a CT image that contain abrupt changes in tissue density are electronically represented by which of the following?
A. Positive CT numbers
B. High spatial frequencies
C. Negative CT numbers
D. Low spatial frequencies

high spatial frequencies

42. Fourth-generation CT scanners use a _________________ tube-detector configuration.
A. Rotate - translate
B. Electron beam - stationary
C. Rotate - stationary
D. Rotate - rotate

Rotate - stationary

43. Pixels whose average attenuation coefficients are less than that of water have which of the following types of CT number values?
A. Extremely large
B. High positive
C. Negative
D. None of the above


44. Which of the following archival media is capable of storing the largest number of CT images?
A. Floppy disk
B. Magnetic tape
C. VHS tape
D. Optical disk

Optical disk

45. Which of the following types of gas is commonly used for gas ionization CT detectors?
A. Xenon
B. Cadmium tungstate
C. Helium
D. Nitrogen


46. Which of the following is an analytic form of image reconstruction?1. iterative technique2. Fourier reconstruction3. filtered back-projection
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3

2 and 3 only

47. An accurate, modern CT scanner is capable of a spatial resolution of up to:
A. 10 lp/mm
B. 20 lp/mm
C. 10 lp/cm
D. 20 lp/cm


48. The component of the CT scanner responsible for the mathematical calculations of the image reconstruction is the:
A. Data acquisition system (DAS)
B. Analog-to-analog converter
C. Digital-to-analog converter
D. Array Processor

Array Processor

49. Ring artefacts on the CT image are associated with which of the following tube-detector geometric relationships?
A. Rotate-nutate
B. Rotate-stationary
C. Rotate-rotate
D. Translate-rotate


50. Which of the following reconstruction methods is used by most modern CT Scanners?
A.Back projection
B.Iterative methods
C. Fourier transform
D. Filtered back-projection

Filtered back-projection

51. CT numbers are usually provided in the form of:
A. Hounsfield units
B. Electromagnetic interference numbers
C. Cormacks
D. U

Hounsfield units

52. Which of the following increases the signal-to-noise ratio of a CT image?
A. Decreased aperture size
B. Decreased miliampere-seconds (mAs)
C. Increased filtration
D. Increased aperture size

Increased aperture size

53. Which of the following statements regarding retrospective image reconstruction is false?
A. The algorithm, matrix size, and DFOV may all be changed.
B. The slice thickness and SFOV may be changed
C. Scan (raw) data must be available
D. Retrospective i

The slice thickness and SFOV may be changed

54. A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a:
A. Pixel
B. Voxel
C. Matrix
D. Reformat