CT Registry Physics Hhh

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Quizzes Created: 3 | Total Attempts: 7,100
Questions: 14 | Attempts: 3,747

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Understanding physics for ct registry

Questions and Answers
• 1.

The full width at half maximum (FWHM) of a CT scanner is used to describe:

• A.

Spatial resolution

• B.

Contrast resolution

• C.

Noise

• D.

Calibration accuracy

Correct Answer
A. Spatial resolution
Explanation
The full width at half maximum (FWHM) is a measure of the width of a peak at half its maximum height. In the context of a CT scanner, the FWHM is used to describe the spatial resolution. Spatial resolution refers to the ability of the scanner to distinguish between two closely spaced objects or details in an image. A smaller FWHM indicates a higher spatial resolution, meaning that the scanner can better differentiate between small structures or details in the image. Therefore, the FWHM is directly related to the spatial resolution of a CT scanner.

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• 2.

Voxels with equal dimensions along the x, y, and z axes are referred to as

• A.

Prospective

• B.

Isotropic

• C.

Retrospective

• D.

Anisotropic

Correct Answer
B. Isotropic
Explanation
Voxels with equal dimensions along the x, y, and z axes are referred to as isotropic. Isotropic means that the voxel has the same size in all three dimensions, resulting in a uniform resolution throughout the volume. This is important in various fields such as medical imaging, where isotropic voxels allow for accurate measurements and consistent representation of structures in all directions.

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• 3.

The average photon energy of the primary beam of a CT scanner operating at a tube potential of 120 kVp is approximately

• A.

50 keV

• B.

70keV

• C.

100 keV

• D.

120 keV

Correct Answer
B. 70keV
Explanation
The average photon energy of the primary beam of a CT scanner operating at a tube potential of 120 kVp is approximately 70 keV. This is because the tube potential represents the maximum energy that the photons can have, and the average photon energy is typically around 70% of the tube potential. Therefore, in this case, the average photon energy would be around 70 keV.

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• 4.

The acquisition of a series of CT images at a single anatomic location over a set period is referred to as;

• A.

Ultrafast ct

• B.

Cine ct

• C.

Conventional ct

• D.

Temporal ct

Correct Answer
B. Cine ct
Explanation
Cine CT refers to the acquisition of a series of CT images at a single anatomic location over a set period. This technique allows for the visualization of dynamic processes, such as the movement of organs or blood flow, by capturing multiple images in quick succession. Unlike conventional CT, which captures a single static image, cine CT provides a time-resolved assessment of the anatomy being scanned. Ultrafast CT and temporal CT are not accurate terms for this specific technique.

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• 5.

The rate at which  a quantity of x-radiation emitted from a CT tube passes through a unit area over a unit of time is called the:

• A.

Effective mAs

• B.

Photon flux

• C.

Constant mAs

• D.

Photon fluence

Correct Answer
B. Photon flux
Explanation
The rate at which a quantity of x-radiation emitted from a CT tube passes through a unit area over a unit of time is called photon flux. This term refers to the number of photons that pass through a specific area in a given time period, indicating the intensity or amount of radiation being emitted. It is a measure of the radiation exposure or dose received by a particular area or object.

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• 6.

A standard CT image reconstructed on a 512 matrix has a digital size of approximately

• A.

0.5 mb

• B.

3.0 MB

• C.

5.0 mb

• D.

10.0 mb

Correct Answer
A. 0.5 mb
Explanation
A standard CT image reconstructed on a 512 matrix has a digital size of approximately 0.5 MB because CT images are composed of a large number of pixels, and the size of each pixel depends on the matrix size. In this case, the 512 matrix size indicates that there are 512 pixels in both the horizontal and vertical directions. The digital size of the image is determined by the number of pixels and the bit depth used to represent each pixel. Since CT images typically have a bit depth of 8 or 16 bits, the digital size of the image is relatively small, resulting in a size of approximately 0.5 MB.

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• 7.

The 3d ct technique that includes all of the acquired voxel information in the reconstructed model with adjustments to its opacity is termed;

• A.

Surface rendering

• B.

MIP

• C.

Curved multiplanar reformation

• D.

Volume rendering

Correct Answer
D. Volume rendering
Explanation
Volume rendering is a 3D CT technique that utilizes all of the acquired voxel information in the reconstructed model. It allows for adjustments to the opacity of the voxels, which enables the visualization of different structures and tissues within the volume. This technique is particularly useful in displaying complex anatomical structures and can provide a more comprehensive understanding of the data compared to other techniques such as surface rendering, MIP, or curved multiplanar reformation.

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• 8.

The contrast resolution of a cT scanner is not related to which of the following

• A.

Focal spot size

• B.

Section width

• C.

Reconstruction algorithm

• D.

Signal-to-noise ratio

Correct Answer
A. Focal spot size
Explanation
The contrast resolution of a cT scanner refers to its ability to distinguish between different shades of gray in an image. It is determined by factors such as section width, reconstruction algorithm, and signal-to-noise ratio. Focal spot size, on the other hand, relates to the sharpness and clarity of the image, but it does not directly affect the contrast resolution. Therefore, the correct answer is focal spot size.

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• 9.

The average photon energy of the ct x-ray beam can be increased by

• A.

Increasing mAs

• B.

Increasing filtration

• C.

Increasing collimation

• D.

All of the above

Correct Answer
B. Increasing filtration
Explanation
Increasing filtration refers to adding additional materials to the x-ray beam in order to absorb low-energy photons. This results in a higher average energy of the remaining photons in the beam. By increasing filtration, the lower energy photons are removed, leaving behind higher energy photons, which increases the average photon energy of the x-ray beam. Therefore, increasing filtration is a valid method to increase the average photon energy of the ct x-ray beam.

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• 10.

The type of MSCT detector array that contains multiple rows of detector elements, each of the same length, is called

• A.

Uniform matrix array

• B.

Adaptive array

• C.

Hybrid array

• D.

Stationary array

Correct Answer
A. Uniform matrix array
Explanation
The correct answer is uniform matrix array. This type of MSCT detector array consists of multiple rows of detector elements, with each row having the same length. This arrangement allows for uniform and consistent detection across the entire array. The uniform matrix array is commonly used in medical imaging applications, such as computed tomography (CT) scans, to capture detailed and accurate images of the patient's anatomy.

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• 11.

Reformatted ct image planes that lie perpendicular to the original plane of acquisition may be described as

• A.

Oblique

• B.

Orthogonal

• C.

Obtuse

• D.

Orthographic

Correct Answer
B. Orthogonal
Explanation
Orthogonal refers to the relationship between two lines or planes that are at right angles to each other. In the context of a CT scan, if the image planes are reformatted to be perpendicular to the original plane of acquisition, they are considered orthogonal. This means that the new image planes are at a 90-degree angle to the original plane, allowing for a clear and accurate representation of the anatomy being examined.

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• 12.

Segmenting the data acquisiton process into separate componenets of smaller rotation angles may improve which of the following componenets of CT image quality

• A.

Temporal resolution

• B.

Longitudinal spatial resolution

• C.

Contrast resolution

• D.

In-plane spatial resolution

Correct Answer
A. Temporal resolution
Explanation
Segmenting the data acquisition process into smaller rotation angles allows for faster image acquisition, resulting in improved temporal resolution. Temporal resolution refers to the ability to capture and distinguish changes over time. By acquiring data at smaller rotation angles, the CT scanner can capture images more frequently, allowing for better visualization of dynamic processes and reducing motion artifacts. Therefore, improving temporal resolution is the likely outcome of segmenting the data acquisition process.

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• 13.

Which of the following image artifacts is unique to multislice CT (MSCT) systems

• A.

Step artifact

• B.

Aliasing artifact

• C.

Out of fild artifact

• D.

Cone beam artifact

Correct Answer
D. Cone beam artifact
Explanation
The cone beam artifact is unique to multislice CT (MSCT) systems. This artifact occurs when the X-ray beam is not perfectly aligned with the detectors, resulting in streaks or shadows appearing in the reconstructed image. This artifact is specific to MSCT systems because they use a cone-shaped X-ray beam to acquire data from multiple slices simultaneously, which increases the likelihood of misalignment and the occurrence of cone beam artifacts.

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• 14.

A 16-slice MSCT system utilizes an adaptive array of 24 detectors, each ranging in size from 0.625 to 1.25 mm What is the maximum number of sections the system can acquire with each rotation of the gantry

• A.

8

• B.

16

• C.

32

• D.

64

Correct Answer
B. 16
Explanation
The maximum number of sections the system can acquire with each rotation of the gantry is 16. This is because the MSCT system has a 16-slice configuration, meaning it can capture 16 sections or images simultaneously. Each detector in the adaptive array ranges in size from 0.625 to 1.25 mm, which allows for the acquisition of 16 sections in a single rotation.

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