Mosby CT Registry Review
What is the smallest component of a digital image - correct answer pixel
How many CT numbers are assigned to each pixel in the image matrix? - correct
answer One
In a CT image, the CT number - correct 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 -
correct answer pixel
What is an element of the digital image - correct answer pixel
Which of the following influences the spatial resolution in cardiac CT imaging -
correct answer *detector size
*reconstruction interval
*pitch
As patient motion increases spatial resolution decreases - correct answer TRUE
Which is an advantage of using a small focal spot - correct answer increased
spatial resolution
Increasing the CT image matrix from 256x256 to 512x512 will likely improve? -
correct 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? - correct answer 1.4 mm
Use of a bone filter, as opposed to a soft tissue filter, to reconstruct CT images
would likely improve? - correct answer Spatial resolution
The spatial resolution of a typical CT scanner is on the order of? - correct 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? - correct answer 8.5
When comparing a 512x512 matrix to a 1024x1024 matrix, the 1024x1024
matrix? - correct answer Contains four times as many pixels: 1024 x 1024
=1048576 then 512 x 512= 262144...then divide 1048576 /262144 = 4
,Mosby CT Registry Review
High contrast spatial resolution and low contrast resolution are typically
measured baseline and ? thereafter - correct answer Biannually
To improve the high contrast spatial resolution of a CT study, one would increase
_____ while keeping all other factors the same. - correct 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 - correct 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? - correct 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? - correct answer 0
How many pixels are contained in a 1,024 matrix image? - correct answer D.
1,048,576
MATH 1024 X1024
It is located in a matrix and is a two dimensional representation of a voxel -
correct 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 - correct answer
pixel
What is defined as a picture element or the smallest component of the digital
image - correct 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. - correct 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? - correct answer spatial resolution
,Mosby CT Registry Review
Which of the following terms is/are commonly used to describe a CT scanner's
ability to differentiate objects with similar linear attenuation coeffiecents -
correct answer *spatial resolution
*sensitivity
Which of the following factors have an affect on contrast resolution - correct
answer *patient size
*slice thickness
*pixel size
*mAs/dose
As mAs/dose increases contrast resolution decreases - correct answer FALSE
As mAs/dose increases contrast resolution INCREASES - correct answer TRUE
The ability of a CT scanner to accurately image objects with similar densities is
termed - correct answer *contrast resolution
*sensitivity
Which of the following has a direct relationship on increasing contrast resolution -
correct 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? - correct answer 50. Equation (.21-.20/.21) × 1000= 50
A CT scanner with poor contrast resolution or low sensitivity has difficulty
separating - correct answer tissues whose linear attenuation coefficients are
nearly equal
What is the basic physical quantity being measured by a CT system - correct
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? - correct answer +1,000....Equation { (.4-.2) /.2} x 1000
, Mosby CT Registry Review
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? - correct answer 0.63
The contrast resolution of CT is approximately ? % - correct answer 0.3 to 0.6
This term describes the ability CT scanner to differentiate objects with MINIMAL
differences in attenuation coefficients - correct 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. - correct answer contrast
resolution
In order to pass ACR CT accreditation, the CT scanner's adult head protocol must
be within - correct answer 1.0
The QC test for the average CT number for water should be done - correct
answer Daily
The following are all basic tenets of a QC program for computed tomography
scanner - correct 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 - correct answer CT number uniformity
The following QC test should be done on a monthly basis - correct answer high
contrast resolution
The CT number at the center of a uniformly filled water phantom should ideally
be - correct answer 0
The ACR CT accreditation phantom is designed to perform QC measurements of -
correct 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 - correct answer
+-7HU or +-5 preferred
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