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CT

Partial volume averaging on CT images can be decreased by decreasing slice thickness. Loss of anatomic information between slices due to inconsistent breathing is called misregistration. A CT image is formed by projecting attenuation values recorded during data acquisition onto voxels. With a 512x512 matrix and 25.6 cm DFOV, each pixel is 0.5 mm. First generation CT used a translate-rotate principle. CT numbers are provided in Hounsfield units. Attenuation is the reduction in intensity of an x-ray beam interacting with matter.

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2K views3 pages

CT

Partial volume averaging on CT images can be decreased by decreasing slice thickness. Loss of anatomic information between slices due to inconsistent breathing is called misregistration. A CT image is formed by projecting attenuation values recorded during data acquisition onto voxels. With a 512x512 matrix and 25.6 cm DFOV, each pixel is 0.5 mm. First generation CT used a translate-rotate principle. CT numbers are provided in Hounsfield units. Attenuation is the reduction in intensity of an x-ray beam interacting with matter.

Uploaded by

sameh dra
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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1 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

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

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

What is the dimension of each pixel in an image with a 512x512 mm matrix and a DFOV
equaling 25.6 cm?
a. 0.5mm
b. 0.5cm
c. 0.05cm
d. both a and c

First generation CT scanners used a method of data acquisition based on a ___________


principle.
a. multiplanar
b. rotation only
c. translate-rotate
d. transaxial

CT numbers are usually provided in the form of?


a. Hounsfield units
b. electromagnetic interference numbers
c. Cormacks
The reduction in intensity of an x-ray beam as it interacts with matter is termed?
a. scatter
b. attenuation
c. transmission
d. luminescence

The major disadvantage of the fan-shaped x-ray beam 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

Which of the following is the most common type of noise found in CT images?
a. statistical noise
b. electronic noise
c. artifactual noise
d. filter noise

Scintillation crystals are used exclusively as detectors in _________ CT scanners.


a. electron beam
b. third-generation
c. fourth-generation
d. spiral

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

The CT "window" controls the _______ of the CT image


a. density and detail
b. spatial and contrast resolution
c. contrast and brightness
d. attenuation coefficient and Hounsfield unit
Which of the following decreases the noise of a CT image?
a. decrease in dose
b. decrease in slice thickness
c. increase in matrix
d. decrease in matrix
Quality control measurments to test the accuracy of the calibration of the CT scanner should
be performed?

a. daily
b. weekly
c. monthly
d. annually

Which of the following reduces scatter radiaiton reaching the detectors?


a. postpatient collimation
b. prepatient collimation
c. predetector collimation
d. both a and c

a pixel is defined as?


a. the portion of the CRT displaying the image
b. a volume element
c. a picture element
d. a miniature image

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

Which of the following is the primary interaction between x-ray photons and tissue during Ct
examination?
a. bremsstrahlung effect
b. characteristic effect
c. Compton effect
d. coherent scatter

Ring artifacts on the CT image are associated wih which of the following tube-detector
geometric relationships?
a. rotate-nutate
b. rotate-stationary
c. rotate-rotate
d. translate-rotate

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