Partial volume averaging on the CT image may be decreased by
D. decreasing slice thickness
The loss of anatomic information between contiguous sections due to inconsistent patient breathing is called
B. misregistration
A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a
C. matrix
What is the dimension of each pixel in an image with a 512x512mm matrix and a DFOV equaling 25.6cm?
D. both a and c the dimension of a pixel may be calculated by dividing the FOV by the matrix size
The reduction in intensity of an xray beam as it interacts with matter is termed
D. attenuation
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
Which of the following is the most common type of noise found in the CT image?
A. statistical noise
Scintillation crystals are used exclusively as detectors in _______CT scanners
B. fourth-generation
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. 180
Which of the following factors does not affect the dimensions of a voxel?
B. kernel the dimension of a voxel is determined by mutiplying the pixel dimension by the slice thickness
Areas of a CT image that contain abrupt changes in tissue density are electronically represented by which of the following?
D. high spatial frequencies
Which of the following is an analytic form of image reconstruction?
1. iterative technique
2. Fourier reconstruction
3. filtered back-projection
a. 1 only
b. 1 and 2 only
c. 2 and 3 only
d. 1,2, and 3
c. 2 and 3 only
The term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT numbers is
A. linearity
The component of the CT scanner responsible for the mathematical calculations of the image reconstruction process is the
C. array processor
Which of the folowing statements regarding retrospective image reconstruction is false?
A. the slice thickness and the SFOV may be changed
Which of the following decreases the noise of a CT image?
D. decrease in matrix size
Increasing the pitch during a spiral CT examination adversely affects the spatial resolution along with which of the following?
B. z axis
When an operator reduces the SFOV for a particular body part, which of the following technical changes occurs?
C. a smaller number of detectors are activated
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 only
b. 1 and 2 only
c. 1 and 3 only
d. 1, 2, and 3
d. 1, 2, and 3
Which of the following technical parameters would greatly improve the quality of CT studies requiring multiplanar reformats?
C. overlapping scans with narrow section thickness
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
Which of the following reduces scatter radiation reaching the detectors?
D. both a and c
A voxel may be defined as which of the following?
A. a volume element
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 only
b. 1 and 2 only
c. 1 and 3 only
d. 1, 2, and 3
b. 1 and 2 only
A pixel may be defined as
B. a picture element
The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as
D. interpolation
When compared with conventional radiography, CT produces diagnostic images with improved
B. low contrast resolution
In 1917, the Austrian mathematician________ proved that it was possible tp reconstruct a three-dimensional object ftom the infinite set of all its projections
D. Radon
Which of the following is not commonly used as a CT scintillation detector material?
