MOSBY CT REGISTRY REVIEW EXAM
QUESTIONS WITH CORRECT ANSWERS
What is the smallest component of a digital image - Answer-pixel
How many CT numbers are assigned to each pixel in the image matrix? - Answer-One
In a CT image, the CT number - Answer-Of a material is dependent on its linear
attenuation coefficient
Each two-dimensional square of data that make up the CT image is called a - Answer-
pixel
What is an element of the digital image - Answer-pixel
Which of the following influences the spatial resolution in cardiac CT imaging - Answer-
*detector size
*reconstruction interval
*pitch
As patient motion increases spatial resolution decreases - Answer-TRUE
Which is an advantage of using a small focal spot - Answer-increased spatial resolution
Increasing the CT image matrix from 256x256 to 512x512 will likely improve? - Answer-
High-contrast spatial resolution
The practical limiting spatial resolution of a CT scanner is 3.6 lp/cm. What size object
does this correspond to? - Answer-1.4 mm
Use of a bone filter, as opposed to a soft tissue filter, to reconstruct CT images would
likely improve? - Answer-Spatial resolution
The spatial resolution of a typical CT scanner is on the order of? - Answer-1 mm
A 512 x 512 matrix CT image over a 30-cm field of view could show a spatial resolution
of no better than ? lp/cm? - Answer-8.5
When comparing a 512x512 matrix to a 1024x1024 matrix, the 1024x1024 matrix? -
Answer-Contains four times as many pixels: 1024 x 1024 =1048576 then 512 x 512=
262144...then divide 1048576 /262144 = 4
High contrast spatial resolution and low contrast resolution are typically measured
baseline and ? thereafter - Answer-Biannually
,To improve the high contrast spatial resolution of a CT study, one would increase _____
while keeping all other factors the same. - Answer-Matrix size (128x128 to 512x512)
A radiologist wants to improve the high-contrast spatial resolution of anatomy which
he/she is examining by CT. The change which would best lead to this improvement is -
Answer-Increase the matrix size
To improve the high-contrast spatial resolution of a CT study, one could increase ?
while keeping all other factors the same? - Answer-Matrix size
A voxel contains 25% air, 50% water and 25% bone. The CT number for this voxel
would be expected to be _____ HU? - Answer-0
How many pixels are contained in a 1,024 matrix image? - Answer-D. 1,048,576
MATH 1024 X1024
It is located in a matrix and is a two dimensional representation of a voxel - Answer-
pixel
When CT numbers are calculated for voxels (volume elements) of tissue what is
assigned the calculated number and a subsequent shade of gray - Answer-pixel
What is defined as a picture element or the smallest component of the digital image -
Answer-pixel
A CT scan produces a 512x512 matrix transverse image of a 30 cm diameter FOV.
Each pixel is approximately _____ mm on a side. - Answer-0.6 equation:
30cm/512= .058cm convert to mm and its .58 which is approximately 0.6
The ability of a system to define small objects distinctly is referred to as which of the
following? - Answer-spatial resolution
Which of the following terms is/are commonly used to describe a CT scanner's ability to
differentiate objects with similar linear attenuation coeffiecents - Answer-*spatial
resolution
*sensitivity
Which of the following factors have an affect on contrast resolution - Answer-*patient
size
*slice thickness
*pixel size
*mAs/dose
As mAs/dose increases contrast resolution decreases - Answer-FALSE
,As mAs/dose increases contrast resolution INCREASES - Answer-TRUE
The ability of a CT scanner to accurately image objects with similar densities is termed -
Answer-*contrast resolution
*sensitivity
Which of the following has a direct relationship on increasing contrast resolution -
Answer-*mAs/dose increase
*Slice thickness
For a particular CT scanner's beam quality, the linear attenuation coefficient for water is
0.20 cm-1 and for a certain tumor is 0.21 cm-1. What is the CT number of the tumor? -
Answer-50. Equation (.21-.20/.21) × 1000= 50
A CT scanner with poor contrast resolution or low sensitivity has difficulty separating -
Answer-tissues whose linear attenuation coefficients are nearly equal
What is the basic physical quantity being measured by a CT system - Answer-Linear
attenuation coefficient
Assume the linear attenuation coefficient is 0.20 cm-1 for water and 0.40 cm-1 for tissue
within a given voxel. What is the CT number in Hounsfield units for the pixel
representing this voxel? - Answer-+1,000....Equation { (.4-.2) /.2} x 1000
What fraction of monoenergetic x-rays will be absorbed by a 20-cm thick material
having a linear attenuation coefficient of 0.05 cm-1? - Answer-0.63
The contrast resolution of CT is approximately ? % - Answer-0.3 to 0.6
This term describes the ability CT scanner to differentiate objects with MINIMAL
differences in attenuation coefficients - Answer-contrast resolution
What is the term for resolution of a CT scanner referred to as the system's ability to
differentiate objects with SIMILAR densities. - Answer-contrast resolution
In order to pass ACR CT accreditation, the CT scanner's adult head protocol must be
within - Answer-1.0
The QC test for the average CT number for water should be done - Answer-Daily
The following are all basic tenets of a QC program for computed tomography scanner -
Answer-*QC test must be conducted regularly
*Accurate record keeping
*all test results must be interpreted promptly
, Using the ACR CT accreditation phantom, module 3 is used to measure which of the
following - Answer-CT number uniformity
The following QC test should be done on a monthly basis - Answer-high contrast
resolution
The CT number at the center of a uniformly filled water phantom should ideally be -
Answer-0
The ACR CT accreditation phantom is designed to perform QC measurements of -
Answer-*positioning accuracy and light accuracy alignment only
*CT number accuracy and slice thickness only
*low contrast resolution, CT number uniformity, and high contrast resolution
The ACR tolerance limit for the CT number accuracy for water is - Answer-+-7HU or +-5
preferred
The test for the average CT number of water should be tested at - Answer-*acceptance
*daily
The ACR tolerance limit for the CT number uniformity is which of the following - Answer-
The center CT number must be between plus or minus 7HU plus the abdomen protocol
must be used
To evaluate low contrast resolution, phantoms are scanned using different ? settings -
Answer-mAs
For an increase from 200 mA to 400 mA in a CT exam, the result would be to - Answer-
Increase low contrast resolution
This ability is also commonly referred to as the low contrast resolution or the sensitivity
of the CT scanner - Answer-contrast resolution
The major advantage of a CT scanner over a screen-film radiography system is -
Answer-Better low contrast discrimination
For CT images, all of the following factors improve the visibility of large, low-contrast
lesions except? - Answer-Smaller pixel sizes
As the iodine concentration ? the viscosity of the substance will ? - Answer-increase,
increase
A fluid with a high viscosity is relatively - Answer-thick and flows slowly
The viscosity of a solution may be changed by regulating - Answer-temperature
QUESTIONS WITH CORRECT ANSWERS
What is the smallest component of a digital image - Answer-pixel
How many CT numbers are assigned to each pixel in the image matrix? - Answer-One
In a CT image, the CT number - Answer-Of a material is dependent on its linear
attenuation coefficient
Each two-dimensional square of data that make up the CT image is called a - Answer-
pixel
What is an element of the digital image - Answer-pixel
Which of the following influences the spatial resolution in cardiac CT imaging - Answer-
*detector size
*reconstruction interval
*pitch
As patient motion increases spatial resolution decreases - Answer-TRUE
Which is an advantage of using a small focal spot - Answer-increased spatial resolution
Increasing the CT image matrix from 256x256 to 512x512 will likely improve? - Answer-
High-contrast spatial resolution
The practical limiting spatial resolution of a CT scanner is 3.6 lp/cm. What size object
does this correspond to? - Answer-1.4 mm
Use of a bone filter, as opposed to a soft tissue filter, to reconstruct CT images would
likely improve? - Answer-Spatial resolution
The spatial resolution of a typical CT scanner is on the order of? - Answer-1 mm
A 512 x 512 matrix CT image over a 30-cm field of view could show a spatial resolution
of no better than ? lp/cm? - Answer-8.5
When comparing a 512x512 matrix to a 1024x1024 matrix, the 1024x1024 matrix? -
Answer-Contains four times as many pixels: 1024 x 1024 =1048576 then 512 x 512=
262144...then divide 1048576 /262144 = 4
High contrast spatial resolution and low contrast resolution are typically measured
baseline and ? thereafter - Answer-Biannually
,To improve the high contrast spatial resolution of a CT study, one would increase _____
while keeping all other factors the same. - Answer-Matrix size (128x128 to 512x512)
A radiologist wants to improve the high-contrast spatial resolution of anatomy which
he/she is examining by CT. The change which would best lead to this improvement is -
Answer-Increase the matrix size
To improve the high-contrast spatial resolution of a CT study, one could increase ?
while keeping all other factors the same? - Answer-Matrix size
A voxel contains 25% air, 50% water and 25% bone. The CT number for this voxel
would be expected to be _____ HU? - Answer-0
How many pixels are contained in a 1,024 matrix image? - Answer-D. 1,048,576
MATH 1024 X1024
It is located in a matrix and is a two dimensional representation of a voxel - Answer-
pixel
When CT numbers are calculated for voxels (volume elements) of tissue what is
assigned the calculated number and a subsequent shade of gray - Answer-pixel
What is defined as a picture element or the smallest component of the digital image -
Answer-pixel
A CT scan produces a 512x512 matrix transverse image of a 30 cm diameter FOV.
Each pixel is approximately _____ mm on a side. - Answer-0.6 equation:
30cm/512= .058cm convert to mm and its .58 which is approximately 0.6
The ability of a system to define small objects distinctly is referred to as which of the
following? - Answer-spatial resolution
Which of the following terms is/are commonly used to describe a CT scanner's ability to
differentiate objects with similar linear attenuation coeffiecents - Answer-*spatial
resolution
*sensitivity
Which of the following factors have an affect on contrast resolution - Answer-*patient
size
*slice thickness
*pixel size
*mAs/dose
As mAs/dose increases contrast resolution decreases - Answer-FALSE
,As mAs/dose increases contrast resolution INCREASES - Answer-TRUE
The ability of a CT scanner to accurately image objects with similar densities is termed -
Answer-*contrast resolution
*sensitivity
Which of the following has a direct relationship on increasing contrast resolution -
Answer-*mAs/dose increase
*Slice thickness
For a particular CT scanner's beam quality, the linear attenuation coefficient for water is
0.20 cm-1 and for a certain tumor is 0.21 cm-1. What is the CT number of the tumor? -
Answer-50. Equation (.21-.20/.21) × 1000= 50
A CT scanner with poor contrast resolution or low sensitivity has difficulty separating -
Answer-tissues whose linear attenuation coefficients are nearly equal
What is the basic physical quantity being measured by a CT system - Answer-Linear
attenuation coefficient
Assume the linear attenuation coefficient is 0.20 cm-1 for water and 0.40 cm-1 for tissue
within a given voxel. What is the CT number in Hounsfield units for the pixel
representing this voxel? - Answer-+1,000....Equation { (.4-.2) /.2} x 1000
What fraction of monoenergetic x-rays will be absorbed by a 20-cm thick material
having a linear attenuation coefficient of 0.05 cm-1? - Answer-0.63
The contrast resolution of CT is approximately ? % - Answer-0.3 to 0.6
This term describes the ability CT scanner to differentiate objects with MINIMAL
differences in attenuation coefficients - Answer-contrast resolution
What is the term for resolution of a CT scanner referred to as the system's ability to
differentiate objects with SIMILAR densities. - Answer-contrast resolution
In order to pass ACR CT accreditation, the CT scanner's adult head protocol must be
within - Answer-1.0
The QC test for the average CT number for water should be done - Answer-Daily
The following are all basic tenets of a QC program for computed tomography scanner -
Answer-*QC test must be conducted regularly
*Accurate record keeping
*all test results must be interpreted promptly
, Using the ACR CT accreditation phantom, module 3 is used to measure which of the
following - Answer-CT number uniformity
The following QC test should be done on a monthly basis - Answer-high contrast
resolution
The CT number at the center of a uniformly filled water phantom should ideally be -
Answer-0
The ACR CT accreditation phantom is designed to perform QC measurements of -
Answer-*positioning accuracy and light accuracy alignment only
*CT number accuracy and slice thickness only
*low contrast resolution, CT number uniformity, and high contrast resolution
The ACR tolerance limit for the CT number accuracy for water is - Answer-+-7HU or +-5
preferred
The test for the average CT number of water should be tested at - Answer-*acceptance
*daily
The ACR tolerance limit for the CT number uniformity is which of the following - Answer-
The center CT number must be between plus or minus 7HU plus the abdomen protocol
must be used
To evaluate low contrast resolution, phantoms are scanned using different ? settings -
Answer-mAs
For an increase from 200 mA to 400 mA in a CT exam, the result would be to - Answer-
Increase low contrast resolution
This ability is also commonly referred to as the low contrast resolution or the sensitivity
of the CT scanner - Answer-contrast resolution
The major advantage of a CT scanner over a screen-film radiography system is -
Answer-Better low contrast discrimination
For CT images, all of the following factors improve the visibility of large, low-contrast
lesions except? - Answer-Smaller pixel sizes
As the iodine concentration ? the viscosity of the substance will ? - Answer-increase,
increase
A fluid with a high viscosity is relatively - Answer-thick and flows slowly
The viscosity of a solution may be changed by regulating - Answer-temperature
