CT image Formation

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39 terms

B) The scanner must utilize continuous rottation

Which of the following is true regarding the requirements of a CT system capable of performing helical scans: A) the scanner must be of the 4th generation geometry B) The scanner must utilize continuous rottation C) the tube heat stoeage capacity must be at least 6MHU D) all of these

D) none of these

A retrospective reconstruction, in which the reconstruction field-of-view is varied, utilizes which of the following: A) a 3D surface rendering B) CT image data C) a reconstructed image in the dagittal plane D) none of these

D) they both produce digital images

Which is of the following is common to both a localizer scan and a conventional CT scan: A) the x-ray tube makes complete 360 degree rotation B) the patient table moves at a a constant velocity C) they both produce cross-sectional images D) they both produce digital images

D) none of these

Which of the following statements is false: A) the amplified electrical signal obtained from the detectors must be digitized B) digital CT images are numerical representations of cross-sectional anatomy C) digital signals may be formed by sampling analog signals at discrete time intervals D) none of these

D) filtered back projection

What is the mathematical process used by most of the commercially available CT scanners to reconstruct images from raw data: A) the Fourier transform B) weighted averaging C) integration of the area under the curve D) filtered back projection

A) CT image data

3D surface renderings are performed on which of the following: A) CT image data B) CT raw data C) all of these D) none of these

B) a single 2D picture element within the image plane

Which of the following defines a pixel: A) a single 3D volume element within a volume of anatomical data B) a single 2D picture element within the image plane C) a range of gray levels on a CT image D) a bright artifact on a film

D) ray

What term describes the pencil thin section of the x-ray fan beam that strikes a single detector: A) projection B) view C) line D) ray

D) none of these

What is a kernel: A) a type of detector B) a component in the x-ray tube C) a post-processing filter applied to image data D) none of these

D) all of these

Which of the following affects the brightness of the pixels in a CT image: A) the tube voltage B) collimation C) the number of photons absorbed by the patient D) all of these

C) the detector elements

Which of the following does not rotate during a helical scan on a 4th generation scanner: A) the x-ray tube B) the anode C) the detector elements D) none of these

C) the volume data, from which the surface rendering is generated, is created by combining transverse, sagittal, and coronal reconstruction

Which of the following statements is false regarding 3D surface rendering: A) patient motion during the scan is detrimental to the quality of the 3D images B) helical image data is well suited for 3D rendering because there is minimal misregistration or gaps C) the volume data, from which the surface rendering is generated, is created by combining transverse, sagittal, and coronal reconstruction D) the tissue surface may be selected by using a threshold value equal to the tissue's CT number

D) all of these

Which types of storage media may hold CT image data: A)internal hard disk magnetic tape B) magnetic tape C)re-writable optical disk D) all of these

C) pitch

What term is defined as: "the table increment in mm per 360° rotation divided by the slice thickness in mm": A)angle B) helix C) pitch D) none of these

A) patients may hold their breath for a shorter period of time

Which of the following is not an advantage of a helical study compared to a conventional CT study: A) patients may hold their breath for a shorter period of time B) shorter total exam time C) minimal anatomical misregistration sometimes caused by inconsistent breath-holding D) can retrospectively reconstruct a slice at any arbitrary position

C) filtered back projection

Which of the following utilizes convolution: A) 3D surface rendering B) Fourier transform C) filtered back projection D) none of these

D) 0.6

Which of the following helical scanning pitches would acquire overlapping anatomical data: A) 2.0 B)1.4 C)1.0 D)0.6

A) stacked contiguous transverse image

From which of the following can the most diagnostic multi-planar reconstruction be generated: A) stacked contiguous transverse images B) stacked non-contiguous transverse images C) stacked localizer images D) none of these

C) CT raw data

Which of the following contains the actual attenuation data measured by the detectors from all projections during a scan: A) CT image data B) CT convolved data C)CT raw data D) all of these

b) if the pitch increases, the patient dose decreases

The x-ray dose to patient increases the longer the patient is exposed to the x-ray beam. If all other parameter remain unchaned, which of the following is true regarding patient dose & pitch of a helical scan through a given volume: A)if the pitch increases, the patient dose increases b) if the pitch increases, the patient dose decreases C) the patient dose is independent of the pitch D) none of these

A) increase in contrast resolution

Which of the following dose not occur in the resulting images when applying a sharp. or high-pass reconstruction filter during the back projection of CT raw data: A)increase in contrast resolution B) increase in edge enhancement C) increase in noise D) all of these

B) 129,600

If an image matrix has 360 rows & 360 columns, how many pixeles are there in the image: A) 21,600 B)129,600 C)259,200 D) none of these

B) the pixel values in the image data

Which of the following determines the intensity of the laser beam in a laser camera: A) the intensifing grid B) the pixel values in the image data C)the magnifying power of the lens D) none of these

C) retrospective reconstruction

Which of the following is a reconstruction technique applied to the raw data after the primary reconstruction has already been accomplished: A) ost-reconstruction B) secondary reconstruction C) retrospective reconstruction D)none of these

D) enhances the edges of attenuation profiles thus reducing streak and star artifacts

What dose convolution do to the image quality when it is addes to the back projection reconstruction process: A) improves contrst resolution by reducing scatter radiation B) increases the number of projections thereby reducing streaking artifacts C) normalizes the attenuation coefficients to ensure tissuses are displayed with correct CT numbers D) enhances the edges of attenuation profiles thus reducing streak and star artifacts

D) none of these

Which of the following may not occur during the interscan delay of a conventional CT scan preformed on a continuous rotation scanner: A) the table postion is incremented B) the tube continues to rotate in the same direction as during the scan C) the tube assembly makes 360 dregree rotation D) none of these

D) none of these

Which of the following allows helnical data to be converted into planar raw data: A) convolution B) back projection C)retrospective reconstruction D) none of these

A) single emulsion

What is the most common type of film used for recording CT images: A) single emulsion B) double emulsion C) triple emulsion D) none of these

A) a set of logical or mathematical instructions

Which of the following defines an algorithm: A) a set of logical or mathematical instructions B) a measurement of attenuation data C) a post-processing filter D) an analog to digital conversion

A) the number of projection is doubled

A CT system manufactuter has designed a scanner in which the focal spot of the x-ray beam can move to two, slightly separated, distinct locations. What benefit dose the dual focal spot provide copared to an identical scanner possessing a single focal spot: A) the number of projection is doubled B) the number of rays in a single projection is doubled C) the patient dose is halved D)all of these

C)715,000

If there are 715 detectors on a 3rd generation scanner & there are 900 projections in a full rotation, how many samples of attenuation data are collected for the raw data of a single slice if the scan for an overscan of a 400 degree rotation: A) 286,00 B) 643,500 C) 715,00 D) none of these

B) internal auditiory canals

A soft, or low-pass, reconstruction filter should not be selected for the following patient exam: A) pituitary B) internal auditiory canals C) kidneys D) liver

C) the table increment per 360 degree rotation is egual to the slice thickness

What dose a pitch of 1 represent on a helical scan: A) slice thickness = 1 cm B) skice thickness = 1mm C) the table increment per 360 degree rotation is egual to the slice thickness D) none of these

B) attenuated by the patient's tissuese

The x-ray beam used in CT scanning is: A) reflected off the patient's tissues B) attenuated by the patient's tissuese C) generated by the patient's tissues D) none of these

B) pitch > 1

Which of the following helical pitches allows 1mm skices of 40mm of anatomy to be scanned in a single breath-hold if the maximum breath-hold of a patient is 20sec. (assume the tube makes a complete 360 dregree rotation in 1 sec.): A) pitch < 1 B) pitch > 1 C) pitch = 1 D) impossible to scan the anatomy with 1 mm slices during a sigle breath-hold

A) a soft, or low-pass, reconstruction filter does not enhance the edges of the raw data attenuation profiles

Which of the following statements is false: A) a soft, or low-pass, reconstruction filter does not enhance the edges of the raw data attenuation profiles B) a sharp, or high-pass, reconstruction filter does enhance the edges of the raw data attenuation profiless C) reconstruction filters are applied during the back projection process D)reconstruction filters are convolved with the raw data

B) two slices may be generated simultaneously

A CT system manufacturer has designed a scanner in which there are two rows of detectors adjacent to each other along the z-direction. What benefit does the double row of detectors provide compared to an identical scanner possessing a single row of detectors: A) the patine dose is halved B) two slices may be generated simultaneously C)image reconstruction time is reduced D) twice the numbers of gray levels are available to differentiate tissues

A) CT image data

Multi-planar reconstruction are performed on which of the following: A) CT image data B) CT raw data C) all of these D) none of these

D) None of these

Which of the following does not move during a helical scan on a 3rd generation scanner: A) the x-ray tube B) the patient table C) the detector elements D) none of these

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