MOSBY CT REGISTRY REVIEW
QUESTIONS AND ANSWERS WITH
SOLUTIONS 2024
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
QUESTIONS AND ANSWERS WITH
SOLUTIONS 2024
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
