# CT Physics And Instrumentation Quiz Questions And Answers

Reviewed by Matt Balanda
Matt Balanda, BS, Science |
Physics Expert
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Matt graduated with a Master's in Educational Leadership for Faith-Based Schools from California Baptist University and a Bachelor's of Science in Aerospace Engineering and Mathematics from the University of Arizona. A devoted leader, transitioned from Aerospace Engineering to inspire students. As the High School Vice-Principal and a skilled Physics teacher at Calvary Chapel Christian School, his passion is nurturing a love for learning and deepening students' connection with God, fostering a transformative educational journey.
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Check out these CT Physics and Instrumentation quiz questions and answers to review your knowledge of this technology. A Computerized Tomography (CT) is a medical imaging technique aimed at a patient and quickly rotated around the body. CT scanner uses a motorized x-ray source that revolves around the circular opening of a donut-shaped structure called a gantry. The quiz below will help you revise what you know about CT physics and instrumentation. Let's play the quiz. Good luck!

Questions and Answers
• 1.

### A pixel may be defined as

• A.

The portion of the CRT displaying the image

• B.

A volume element

• C.

A picture element

• D.

A miniature image

Correct Answer
C. A picture element
Explanation
A pixel is a term used to describe a picture element. It refers to the smallest unit of a digital image or display that can be individually manipulated. Each pixel represents a specific color or shade, and when combined with other pixels, it forms the complete image. Therefore, the correct answer is "a picture element."

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• 2.

### The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as

• A.

Filtering

• B.

Interpolation

• C.

Convolution

• D.

Summation

Correct Answer
B. Interpolation
Explanation
Interpolation is the correct answer because it is the mathematical technique used to estimate an unknown value based on known values on either side of it. It involves constructing a function that fits the known data points and then using that function to find the value of the unknown point. This technique is commonly used in various fields such as mathematics, statistics, and computer science to fill in missing data or to make predictions based on existing data.

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• 3.

### Which of the types of values do the pixels representing tissues with average attenuation coefficients greater than that of water have?

• A.

Extremely small

• B.

Positive

• C.

Negative

• D.

Extremely large

Correct Answer
B. Positive
Explanation
Pixels representing tissues with average attenuation coefficients greater than that of water have positive values. This is because attenuation coefficients represent the ability of a material to absorb or scatter radiation, and tissues with higher attenuation coefficients than water absorb more radiation. Therefore, the pixel values representing these tissues will be positive, indicating the presence of higher attenuation.

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• 4.

### When compared with conventional X-ray, CT produces diagnostic images with improved

• A.

Low contrast resolution

• B.

Spatial resolution

• C.

Minute detail

• D.

PT dose

Correct Answer
A. Low contrast resolution
Explanation
CT (Computed Tomography) produces diagnostic images with improved low contrast resolution when compared with conventional X-ray. Low contrast resolution refers to the ability to distinguish between structures that have similar densities or shades of gray. CT scans use a combination of X-rays and advanced computer processing to create detailed cross-sectional images of the body. This allows for better visualization and differentiation of subtle differences in tissue density, which is especially important for detecting small abnormalities or lesions that may not be easily seen on a conventional X-ray.

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• 5.

### IN 1917, the Austrian mathematician _____________ proved that it was possible to reconstruct a three-dimensional object from the infinite set of all projections.

• A.

Radon

• B.

Tsien

• C.

Bracewell

• D.

Cormack

Correct Answer
A. Radon
Explanation
In 1917, the Austrian mathematician Radon proved that it was possible to reconstruct a three-dimensional object from the infinite set of all projections. This means that by using a collection of two-dimensional images or projections of an object taken from different angles, it is possible to mathematically reconstruct the original three-dimensional object. This breakthrough in mathematics and imaging has had significant applications in fields such as medical imaging, computer vision, and industrial inspection.

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• 6.

### Which of the following is not commonly used as a CT scintillation detector?

• A.

Ceramic rare earth

• B.

Silver halide

• C.

Bismuth germanate

• D.

Cadmium tungstate

Correct Answer
B. Silver halide
Explanation
Silver halide is not commonly used as a CT scintillation detector because it has a low light output and poor energy resolution compared to other materials. Ceramic rare earth, bismuth germanate, and cadmium tungstate are commonly used as CT scintillation detectors due to their high light output and good energy resolution, making them more suitable for detecting and measuring radiation in CT scans.

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• 7.

### If a ROI is placed on an object of interest and the HU measures +1.9 HU, the material is most likely to be

• A.

Fat

• B.

Blood

• C.

Tumor

• D.

Water

Correct Answer
D. Water
Explanation
It measures closest to water so it is water within the object.

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• 8.

### The average window width range for a abdomen is

• A.

200-250 HU

• B.

350-600 HU

• C.

650-850 HU

• D.

900-1200 HU

Correct Answer
B. 350-600 HU
Explanation
The correct answer is 350-600 HU. This range is the average window width for an abdomen. HU stands for Hounsfield units, which is a measurement used in CT scans to determine the density of tissues. This range is commonly used to visualize the abdominal organs and structures, as it allows for differentiation between different types of tissues and helps in detecting abnormalities or pathologies in the abdomen.

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• 9.

### What is the average linear attenuation coefficient coefficient for water?

• A.

.0007

• B.

.155

• C.

.206

• D.

.530

Correct Answer
C. .206
Explanation
The average linear attenuation coefficient for water is .206. This means that water absorbs approximately 20.6% of incident radiation as it passes through. This coefficient is used to measure how much radiation is absorbed by a material, and in the case of water, it is relatively high compared to other materials.

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• 10.

### Which of the following it the primary interaction between x-ray photons and tissue during CT examination

• A.

Bremsstrahlung effect

• B.

Characteristic effect

• C.

Compton effect

• D.

Coherent scatter

Correct Answer
C. Compton effect
Explanation
The primary interaction between x-ray photons and tissue during a CT examination is the Compton effect. This occurs when an incoming x-ray photon interacts with an outer-shell electron in the tissue, causing the photon to scatter and lose some of its energy. This scattering effect is what allows CT scanners to create detailed images of the internal structures of the body. The other options mentioned, such as the Bremsstrahlung effect, characteristic effect, and coherent scatter, are also interactions between x-ray photons and tissue, but they are not the primary interaction in CT examinations.

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• 11.

### Area of the CT image that contain minimal changes in tissue density are electronically represented by

• A.

Positive CT numbers

• B.

High spatial frequencies

• C.

Negative CT numbers

• D.

Low spatial frequencies

Correct Answer
D. Low spatial frequencies
Explanation
Low spatial frequencies represent areas of the CT image that contain minimal changes in tissue density. This is because low spatial frequencies correspond to large-scale structures and smooth variations in density. In contrast, high spatial frequencies represent areas with rapid changes in density, while positive and negative CT numbers indicate the relative density of tissues compared to water. Therefore, the correct answer is low spatial frequencies.

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• 12.

### Ring artifacts on the CT image are associated with which of the following tube detector relationships?

• A.

Rotate-nutate

• B.

Rotate-stationary

• C.

Rotate-rotate

• D.

Translate-rotate

Correct Answer
C. Rotate-rotate
Explanation
Ring artifacts on a CT image are associated with the rotate-rotate tube detector relationship. In this relationship, both the X-ray tube and the detector rotate simultaneously around the patient, capturing data from different angles. Ring artifacts occur when there are inconsistencies or errors in the data acquisition process, resulting in variations in the intensity values along the reconstructed image. These variations appear as rings or circular patterns on the CT image.

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• 13.

### In the binary number system, a byte is a series of ___________ bits of information.

• A.

2

• B.

4

• C.

8

• D.

16

Correct Answer
C. 8
Explanation
A byte is a series of 8

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• 14.

### An accurate, modern CT scanner is capable of spatial resolution of up to

• A.

10 lp/mm

• B.

20 lp/mm

• C.

10 lp/cm

• D.

20 lp/cm

Correct Answer
D. 20 lp/cm
Explanation
The answer is 20 lp/cm because a CT scanner's spatial resolution refers to its ability to distinguish small details in an image. lp/cm stands for line pairs per centimeter, which represents the number of pairs of lines that can be distinguished within a centimeter. Therefore, a higher value of lp/cm indicates a higher spatial resolution, meaning that the CT scanner can differentiate smaller details in the image.

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• 15.

### Which of the following is the best method to reduce respiratory motion of the CT image?

• A.

Good PT-Tech communication

• B.

Reduced scan times

• C.

Use of immobilization devices

• D.

Glucagon administration

Correct Answer
A. Good PT-Tech communication
Explanation
Good PT-Tech communication is the best method to reduce respiratory motion of the CT image. This is because when the patient and the technician have clear and effective communication, the patient can be instructed on how to control their breathing during the scan. By coordinating breath-holds or shallow breathing, respiratory motion can be minimized, resulting in clearer and more accurate CT images. This method is non-invasive and does not require any additional equipment or medications.

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• 16.

### Which of the following statements is correct regarding the radiographic film used to archive CT images 1 It is double emulsion film 2 It is sensitive to ultraviolet light only 3 It may be used in conjunction with multiformat or laser camera

• A.

1 only

• B.

2 only

• C.

3 only

• D.

1 and 3

Correct Answer
C. 3 only
Explanation
The correct answer is 3 only. This means that the statement "It may be used in conjunction with a multiformat or laser camera" is correct. This suggests that the radiographic film used to archive CT images can be used together with a multiformat or laser camera. The other statements, "It is double emulsion film" and "It is sensitive to ultraviolet light only," are incorrect.

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• 17.

### Which of the following reconstruction methods is used by most modern CT scanners

• A.

Back projection

• B.

Iterative method

• C.

Fourier transform

• D.

Filtered back projection

Correct Answer
D. Filtered back projection
Explanation
Filtered back projection is the most commonly used reconstruction method in modern CT scanners. It involves passing the raw projection data through a filter to enhance the image quality and then back projecting it to reconstruct the image. This method is preferred because it is fast, efficient, and provides good image quality. Back projection, iterative methods, and Fourier transform are also used in CT reconstruction, but they are not as commonly used as filtered back projection.

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• 18.

### 4th generation CT scanners use a ___________ tube-detector configuration

• A.

Rotate-translate

• B.

Electron beam-stationary

• C.

Rotate-stationary

• D.

Rotate-rotate

Correct Answer
C. Rotate-stationary
Explanation
4th generation CT scanners use a rotate-stationary tube-detector configuration. In this configuration, the X-ray tube rotates around the patient while the detector remains stationary. This allows for faster scanning times and improved image quality compared to earlier generations. The rotate-stationary configuration also reduces the risk of motion artifacts and provides more accurate and detailed images.

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• 19.

### The process by which electrons are produced at the cathode of a CT X-ray tube is known as:

• A.

Rectification

• B.

Anode heel effect

• C.

Thermionic emission

• D.

Isotropic emission

Correct Answer
C. Thermionic emission
Explanation
Thermionic emission is the process by which electrons are produced at the cathode of a CT x-ray tube. This process involves heating the cathode, causing the release of electrons due to the increased thermal energy. These emitted electrons then travel towards the anode, where they interact with the target material and produce x-rays. Rectification refers to the conversion of alternating current to direct current, anode heel effect is the uneven distribution of x-rays due to the angle of the anode, and isotropic emission is not a recognized term in relation to x-ray production.

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• 20.

### Which of the following increases the signal-to-noise ratio of a CT image

• A.

Decreased aperture size

• B.

Decreased milliampere seconds MAS

• C.

Increased aperture size

• D.

Increased filtration

Correct Answer
C. Increased aperture size
Explanation
Increasing the aperture size of a CT image increases the signal-to-noise ratio. The aperture size refers to the width of the collimator, which determines the amount of X-ray photons that can pass through the patient and reach the detector. By increasing the aperture size, more photons can reach the detector, resulting in a stronger signal. This helps to increase the signal-to-noise ratio, as the signal (desired information) is amplified while the noise (unwanted background information) remains relatively constant. Therefore, increasing the aperture size improves the quality and clarity of the CT image.

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• 21.

### A straight line appearing vertically on the scanogram of a fourth generation CT scanner is a artifact most likely caused by

• A.

Edge gradient

• B.

Detector malfunction

• C.

Tube arching

• D.

Increased aperture size

Correct Answer
B. Detector malfunction
Explanation
A straight line appearing vertically on the scanogram of a fourth generation CT scanner is most likely caused by a detector malfunction. This means that there is an issue with the detector that is responsible for capturing the x-ray signals. This malfunction can result in a straight line artifact appearing on the scanogram. It is important to address this issue as it can affect the accuracy and quality of the CT scan images.

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• 22.

### The acronym CTDI is used to describe which of the following

• A.

A specialized CT imaging technique used to measure bone mineral density

• B.

A quality control test that measures the accuracy of the laser lighting system

• C.

The radiation dose to the PT during the CT scan

• D.

A high speed CT scanner used for cardiac imaging

Correct Answer
C. The radiation dose to the PT during the CT scan
Explanation
CTDI stands for Computed Tomography Dose Index, which is a measurement used to describe the radiation dose received by the patient during a CT scan. It is an important parameter in assessing the safety and potential risks associated with CT imaging. By measuring the radiation dose, healthcare professionals can ensure that the benefits of the CT scan outweigh the potential harm caused by radiation exposure. Therefore, the correct answer is "the radiation dose to the PT during the CT scan."

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• 23.

### What is the DFOV used for a 320x320 matrix image with a pixel dimension of .75 x .75 mm?

• A.

12cm

• B.

24cm

• C.

36cm

• D.

48cm

Correct Answer
B. 24cm
Explanation
The DFOV (Display Field of View) is used to determine the size of the displayed image on a monitor. In this case, the image has a matrix size of 320x320 pixels and each pixel has a dimension of .75 x .75 mm. To calculate the DFOV, we multiply the matrix size by the pixel dimension. Therefore, the DFOV would be 320 x .75 mm = 240 mm. Since 1 cm is equal to 10 mm, the DFOV would be 24 cm.

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• 24.

### The full width at half maximum 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) of a CT scanner refers to the width of the point spread function at half of its maximum intensity. In the context of a CT scanner, spatial resolution is a measure of the scanner's ability to distinguish between small objects or details in an image. A smaller FWHM indicates better spatial resolution, as it means that the scanner can accurately represent smaller structures or features in the image. Therefore, the FWHM of a CT scanner is used to describe its spatial resolution.

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• 25.

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

• A.

50 keV

• B.

70 keV

• C.

100 keV

• D.

120 keV

Correct Answer
B. 70 keV
Explanation
The average photon energy of the primary beam of a CT scanner operating at a tube potential of 120kVp is 70 keV. This is because the average photon energy is approximately equal to two-thirds of the tube potential. Therefore, two-thirds of 120kVp is 80 keV, which is closest to the given answer of 70 keV.

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• 26.

### Which of the following is not the typical matrix used with a modern CT Scanner

• A.

80x80

• B.

256x256

• C.

512x512

• D.

1024x1024

Correct Answer
A. 80x80
Explanation
The given options represent different matrix sizes that can be used with a modern CT Scanner. A higher matrix size indicates a higher resolution, allowing for more detailed images. The size 80x80 is significantly smaller compared to the other options, suggesting that it would not be a typical matrix used with a modern CT Scanner.

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• 27.

### Which of the following statements regarding collimation of the CT x-ray beam is false

• A.

Collimation of the x-ray beam occurs both before and after the beam passes through the PT

• B.

Collimation of the beam occurs in the z-axis thus controlling the thickness

• C.

Increases in collimation increases the intensity of the primary beam

• D.

Collimation of the CT x-ray beam is used to limit the detection of scatter radiation

Correct Answer
C. Increases in collimation increases the intensity of the primary beam
Explanation
Collimation of the CT x-ray beam is used to limit the detection of scatter radiation, not to increase the intensity of the primary beam. Collimation helps to control the size and shape of the x-ray beam, reducing scatter radiation and improving image quality. By narrowing the beam, collimation focuses the radiation on the desired area, reducing scatter radiation that can degrade the image and increase patient dose. Increasing collimation does not increase the intensity of the primary beam; instead, it restricts the beam to a smaller area.

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• 28.

### A quality control procedure determines that the low contrast resolution of a CT image is extremely poor. Causes may include1 increased tube output2 increased electronic noise3 decreased PT dose

• A.

1 only

• B.

1 and 3

• C.

2 and 3

• D.

1, 2, and 3

Correct Answer
C. 2 and 3
Explanation
The correct answer is 2 and 3. This means that the causes for the poor low contrast resolution of a CT image may include increased electronic noise and decreased patient dose. These factors can contribute to a decrease in image quality and make it difficult to distinguish between different shades of gray in the image.

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• 29.

### Where is the High Frequency generator usually located in a modern CT scanner

• A.

Inside the gantry

• B.

Just outside the scan room

• C.

Beneath the CT table

• D.

Inside the operators console

Correct Answer
A. Inside the gantry
Explanation
The High Frequency generator is usually located inside the gantry of a modern CT scanner. This placement allows for efficient and direct power supply to the X-ray tube, which is also located in the gantry. By having the generator inside the gantry, it reduces the need for long cables and minimizes energy loss, resulting in more accurate and reliable imaging. Additionally, having the generator within close proximity to the X-ray tube allows for better control and synchronization of the scanning process.

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• 30.

### The information included during the three dimensional reconstruction of a CT scan is controlled by

• A.

Algorithm

• B.

Window setting

• C.

Threshold setting

• D.

Gray scale map

Correct Answer
C. Threshold setting
Explanation
During the three dimensional reconstruction of a CT scan, the information included is controlled by the threshold setting. This setting determines the range of pixel values that will be included in the final reconstructed image. By adjusting the threshold, certain structures or densities can be highlighted or excluded, allowing for better visualization and analysis of specific areas of interest. This setting helps in distinguishing between different tissues and structures based on their density levels, thereby enhancing the accuracy and clarity of the reconstructed image.

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• 31.

### Which of the following components of the CT image quality may be controlled by the tech1 spatial resolution2 contrast resolution3 noise

• A.

2 only

• B.

3 only

• C.

1 and 3

• D.

1, 2, and 3

Correct Answer
D. 1, 2, and 3
Explanation
Spatial resolution, contrast resolution, and noise are all components of CT image quality that can be controlled by the technician. Spatial resolution refers to the ability of the CT scanner to distinguish between small objects or structures in the image. Contrast resolution refers to the ability of the scanner to differentiate between tissues with similar densities. Noise refers to the random variations in pixel values that can reduce image quality. Technicians can adjust the scanning parameters to optimize these components and improve the overall image quality.

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• 32.

### The device constructed to house the x-ray tube and data acquisition system for a CT scanner is termed that

• A.

Central processing unit

• B.

Generator

• C.

Array processor

• D.

Gantry

Correct Answer
D. Gantry
Explanation
The device constructed to house the x-ray tube and data acquisition system for a CT scanner is called a gantry. The gantry is a large, circular structure that rotates around the patient during a CT scan. It houses the x-ray tube, detectors, and other components necessary for capturing the images. The gantry plays a crucial role in positioning and moving the x-ray tube and detectors to acquire the necessary data for creating detailed cross-sectional images.

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• 33.

### Partial volume averaging occurs within a renal cyst during a spiral CT scan of the abdomen. Which of the following technical adjustments could reduce the partial volume effect and provide more accurate CT numbers1 retrospective reconstruction of scan using reduced section thickness2 rescanning of the PT using reduced section thickness3 retrospective reconstruction of the scan using reduced section spacing

• A.

2 only

• B.

1 and 2

• C.

2 and 3

• D.

1. 2. and 3

Correct Answer
C. 2 and 3
Explanation
Retrospective reconstruction of the scan using reduced section spacing and rescanning of the patient using reduced section thickness could both reduce the partial volume effect and provide more accurate CT numbers. By reducing the section thickness and spacing, the images obtained will have a higher spatial resolution, allowing for better differentiation of structures within the renal cyst. This reduces the mixing or averaging of different tissues that can occur with larger section thickness and spacing, resulting in more accurate CT numbers. Therefore, options 2 and 3 are the correct choices.

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• 34.

### A 512x512 image consists of how many pixels?

• A.

512

• B.

1024

• C.

26214

• D.

262144

Correct Answer
D. 262144
Explanation
A 512x512 image consists of 262,144 pixels. This is because to calculate the total number of pixels in an image, we multiply the number of pixels in the width (512) by the number of pixels in the height (512), resulting in 262,144 pixels in total.

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• 35.

### The Hounsfield value of a pixel is directly related to which of the following

• A.

Window width

• B.

Field of view size

• C.

U of H2O

• D.

Window level

Correct Answer
C. U of H2O
Explanation
The Hounsfield value of a pixel is directly related to the attenuation coefficient of the material through which the X-ray beam passes. The attenuation coefficient is influenced by the atomic number and density of the material. The u of H2O refers to the linear attenuation coefficient of water, which is used as a reference material for calibrating the Hounsfield scale. Therefore, the Hounsfield value of a pixel is directly related to the u of H2O.

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• 36.

### The term ___________ describes the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients.

• A.

Spatial resolution

• B.

Contrast resolution

• C.

Linearity

• D.

Modulation

Correct Answer
B. Contrast resolution
Explanation
Contrast resolution refers to the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients. This means that the scanner can distinguish between tissues or structures that have very similar densities or shades of gray on the CT image. A higher contrast resolution allows for better visualization and distinction of subtle differences in tissue density, which is particularly important in detecting small lesions or abnormalities.

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Matt Balanda |BS, Science |
Physics Expert
Matt graduated with a Master's in Educational Leadership for Faith-Based Schools from California Baptist University and a Bachelor's of Science in Aerospace Engineering and Mathematics from the University of Arizona. A devoted leader, transitioned from Aerospace Engineering to inspire students. As the High School Vice-Principal and a skilled Physics teacher at Calvary Chapel Christian School, his passion is nurturing a love for learning and deepening students' connection with God, fostering a transformative educational journey.

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• Nov 30, 2023
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• Sep 15, 2008
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