Computed Tomography Review Questions
With Solved Solutions
Which of the following best represents typical bone window settings? - ANSWER>>WW
1800, WL 400
beam pitch - ANSWER>>table feed per rotation / the total collimation
In an MSCT system, the detector array is composed of multiple rows of individual
detector elements along the: - ANSWER>>z-axis
Detector configuration refers to _____. - ANSWER>>the number, length, and
organization of the individual detector elements in an MSCT system.
Noncontiguous images are images acquired - ANSWER>>with an interval greater than
the section width.
Beam collimation - ANSWER>>(Detector size) x (Desired # of exposed detectors)
CT images that have been reconstructed from a portion of the data acquisition process
in the hopes of reducing patient motion artifacts are called: - ANSWER>>segmented
images
As a solid-state CT detector measures transmitted radiation, it emits a proportional
response in the form of a(n): - ANSWER>>analog system
During a CT scan, each sample of ray sum measurements made by the data acquisition
system (DAS) is called a: - ANSWER>>view
Which of the following is not an iterative method of CT image reconstruction? -
ANSWER>>Fourier transform
The iterative methods of CT image reconstruction include simultaneous reconstruction,
ray-by-ray correction, and point-by-point correction. The Fourier transform method is an
analytic method of CT image reconstruction.
Contiguous images are acquired - ANSWER>>with an interval the same as section
width.
,Isotropic//Overlapping images are acquired - ANSWER>>with a higher interval than the
section width.
The z-axis refers to the ______ plane. - ANSWER>>axial
Which of the following is not a function of the DAS? - ANSWER>>Controlling the mA
along the Z axis of the scan.
Thresholding - ANSWER>>allows the user to select the range of pixel values used in a
3-D CT reformation
What is the dimension of each pixel in the matrix of an image with the following
parameters?
FOV = 25.6 cm
Matrix = 512 mm ✕ 512 mm - ANSWER>>.5 mm or .05 cm
fov/matrix = pixel size
256/512
1 cm = 10 mm
Generators located within the gantry are which generation? - ANSWER>>high
frequency
Modern CT scanners rely on ____ to process acquired data. -
ANSWER>>minicomputers
What decreases contrast resolution? - ANSWER>>smaller pixel size
increased pixel size increases contrast resolution b/c a photon is more likely to interact
with the pixel
The following formula is used to calculate the linear attenuation coefficient:
I = I0e-μxThe symbol "x" identifies: - ANSWER>>absorber thickness
The portion of the primary beam interacting with a single detector is known as a: -
ANSWER>>ray
, Which of the following factors will not affect the spatial resolution of a CT scan? -
ANSWER>>kVp setting
What is the display field of view used for a 3202 matrix image with a pixel dimension of
0.75 mm ✕ 0.75 mm? - ANSWER>>DFOV = pixel x matrix size
=0.75 mmx320
=240 mm x 1mm/10 cm
=24 cm
The Hounsfield value of a pixel is directly related to which of the following? -
ANSWER>>μ of H2O
The value of a pixel in Hounsfield units is calculated through a comparison of the linear
attenuation coefficient (μ) of a voxel of tissue to that of water.
The dimensions of a voxel may be calculated as the product of which of the following? -
ANSWER>>pixel size and section width
The pixel is a two-dimensional representation of a voxel. The section width is equal to
the length of the voxel. To calculate the dimensions of a voxel, the pixel dimension must
be multiplied by the section width.
Which of the following formulas may be used to calculate the dimensions of a pixel? -
ANSWER>>Pixel size = DFOV/matrix size
The volume of a voxel may be calculated by multiplying the pixel dimension (mm2) by
the: - ANSWER>>section width
The typical range for possible pixel values in a modern CT system is between: -
ANSWER>>-1024 HU and +3071 HU
The display field of view (DFOV) for a CT series can be changed by using: -
ANSWER>>image data
Which of the following would increase the signal-to-noise ratio of a CT image? -
ANSWER>>Increased aperture size
SNR ratio is increased when a larger amount of x-ray photons are absorbed by the
detectors
With Solved Solutions
Which of the following best represents typical bone window settings? - ANSWER>>WW
1800, WL 400
beam pitch - ANSWER>>table feed per rotation / the total collimation
In an MSCT system, the detector array is composed of multiple rows of individual
detector elements along the: - ANSWER>>z-axis
Detector configuration refers to _____. - ANSWER>>the number, length, and
organization of the individual detector elements in an MSCT system.
Noncontiguous images are images acquired - ANSWER>>with an interval greater than
the section width.
Beam collimation - ANSWER>>(Detector size) x (Desired # of exposed detectors)
CT images that have been reconstructed from a portion of the data acquisition process
in the hopes of reducing patient motion artifacts are called: - ANSWER>>segmented
images
As a solid-state CT detector measures transmitted radiation, it emits a proportional
response in the form of a(n): - ANSWER>>analog system
During a CT scan, each sample of ray sum measurements made by the data acquisition
system (DAS) is called a: - ANSWER>>view
Which of the following is not an iterative method of CT image reconstruction? -
ANSWER>>Fourier transform
The iterative methods of CT image reconstruction include simultaneous reconstruction,
ray-by-ray correction, and point-by-point correction. The Fourier transform method is an
analytic method of CT image reconstruction.
Contiguous images are acquired - ANSWER>>with an interval the same as section
width.
,Isotropic//Overlapping images are acquired - ANSWER>>with a higher interval than the
section width.
The z-axis refers to the ______ plane. - ANSWER>>axial
Which of the following is not a function of the DAS? - ANSWER>>Controlling the mA
along the Z axis of the scan.
Thresholding - ANSWER>>allows the user to select the range of pixel values used in a
3-D CT reformation
What is the dimension of each pixel in the matrix of an image with the following
parameters?
FOV = 25.6 cm
Matrix = 512 mm ✕ 512 mm - ANSWER>>.5 mm or .05 cm
fov/matrix = pixel size
256/512
1 cm = 10 mm
Generators located within the gantry are which generation? - ANSWER>>high
frequency
Modern CT scanners rely on ____ to process acquired data. -
ANSWER>>minicomputers
What decreases contrast resolution? - ANSWER>>smaller pixel size
increased pixel size increases contrast resolution b/c a photon is more likely to interact
with the pixel
The following formula is used to calculate the linear attenuation coefficient:
I = I0e-μxThe symbol "x" identifies: - ANSWER>>absorber thickness
The portion of the primary beam interacting with a single detector is known as a: -
ANSWER>>ray
, Which of the following factors will not affect the spatial resolution of a CT scan? -
ANSWER>>kVp setting
What is the display field of view used for a 3202 matrix image with a pixel dimension of
0.75 mm ✕ 0.75 mm? - ANSWER>>DFOV = pixel x matrix size
=0.75 mmx320
=240 mm x 1mm/10 cm
=24 cm
The Hounsfield value of a pixel is directly related to which of the following? -
ANSWER>>μ of H2O
The value of a pixel in Hounsfield units is calculated through a comparison of the linear
attenuation coefficient (μ) of a voxel of tissue to that of water.
The dimensions of a voxel may be calculated as the product of which of the following? -
ANSWER>>pixel size and section width
The pixel is a two-dimensional representation of a voxel. The section width is equal to
the length of the voxel. To calculate the dimensions of a voxel, the pixel dimension must
be multiplied by the section width.
Which of the following formulas may be used to calculate the dimensions of a pixel? -
ANSWER>>Pixel size = DFOV/matrix size
The volume of a voxel may be calculated by multiplying the pixel dimension (mm2) by
the: - ANSWER>>section width
The typical range for possible pixel values in a modern CT system is between: -
ANSWER>>-1024 HU and +3071 HU
The display field of view (DFOV) for a CT series can be changed by using: -
ANSWER>>image data
Which of the following would increase the signal-to-noise ratio of a CT image? -
ANSWER>>Increased aperture size
SNR ratio is increased when a larger amount of x-ray photons are absorbed by the
detectors
