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Questions and Answers
What is the effect of increasing the field of view on spatial resolution?
What is the effect of increasing the field of view on spatial resolution?
- It does not affect spatial resolution
- It decreases spatial resolution (correct)
- It has no significant effect on image quality
- It increases spatial resolution
What is the relationship between pixel size and spatial resolution?
What is the relationship between pixel size and spatial resolution?
- Larger pixel size results in higher spatial resolution
- Smaller pixel size results in lower spatial resolution
- Smaller pixel size results in higher spatial resolution (correct)
- Pixel size has no effect on spatial resolution
What is the effect of increasing magnification on spatial resolution?
What is the effect of increasing magnification on spatial resolution?
- It does not affect spatial resolution
- It enhances image contrast
- It increases spatial resolution
- It decreases spatial resolution (correct)
What is the effect of increasing pitch on spatial resolution?
What is the effect of increasing pitch on spatial resolution?
What is the effect of increasing slice thickness on spatial resolution?
What is the effect of increasing slice thickness on spatial resolution?
What is contrast resolution dependent on?
What is contrast resolution dependent on?
What is the limitation of screen-film radiography in terms of contrast resolution?
What is the limitation of screen-film radiography in terms of contrast resolution?
What is temporal resolution controlled by?
What is temporal resolution controlled by?
What is the importance of high temporal resolution in CT imaging?
What is the importance of high temporal resolution in CT imaging?
What is the purpose of the ACR CT accreditation phantom?
What is the purpose of the ACR CT accreditation phantom?
What is the primary factor that determines the usefulness of a CT image?
What is the primary factor that determines the usefulness of a CT image?
What is the unit of measurement for spatial frequency in CT scanners?
What is the unit of measurement for spatial frequency in CT scanners?
Which method is used to graphically represent a system's performance in terms of spatial resolution?
Which method is used to graphically represent a system's performance in terms of spatial resolution?
What is the ability to distinguish between object or structures that differ in density?
What is the ability to distinguish between object or structures that differ in density?
What is the purpose of measuring spatial resolution in CT imaging?
What is the purpose of measuring spatial resolution in CT imaging?
What is the relationship between spatial resolution and line pair phantom?
What is the relationship between spatial resolution and line pair phantom?
What is the primary factor that affects the ability of a CT scanner to distinguish between object or structures that differ in density?
What is the primary factor that affects the ability of a CT scanner to distinguish between object or structures that differ in density?
What is the term used to describe the number of line pairs per unit length?
What is the term used to describe the number of line pairs per unit length?
Which of the following is a measure of CT image quality?
Which of the following is a measure of CT image quality?
What is the purpose of measuring CT image quality?
What is the purpose of measuring CT image quality?
What is the purpose of the phantom in the Slice Thickness QA?
What is the purpose of the phantom in the Slice Thickness QA?
How often is the Noise and Uniformity QA performed?
How often is the Noise and Uniformity QA performed?
What is the acceptable range of CT numbers for air in the CT Number QA?
What is the acceptable range of CT numbers for air in the CT Number QA?
What is the purpose of the phantom in the Contrast Resolution QA?
What is the purpose of the phantom in the Contrast Resolution QA?
How often is the LinearITY QA performed?
How often is the LinearITY QA performed?
What is the purpose of the ROI in the Noise and Uniformity QA?
What is the purpose of the ROI in the Noise and Uniformity QA?
What is the purpose of the phantom in the CT Number QA?
What is the purpose of the phantom in the CT Number QA?
How often is the Slice Thickness and Laser Light Accuracy QA performed?
How often is the Slice Thickness and Laser Light Accuracy QA performed?
What is the acceptable range of CT numbers for water in the CT Number QA?
What is the acceptable range of CT numbers for water in the CT Number QA?
What is the purpose of the phantom in the Linearity QA?
What is the purpose of the phantom in the Linearity QA?
Study Notes
CT Image Quality
- CT image quality is directly related to its usefulness in providing an accurate diagnosis.
Spatial Resolution
- Spatial resolution is the ability to distinguish between objects or structures that differ in density.
- Measured using two methods: directly using a line pairs phantom, or by data analysis known as modulation transfer function (MTF).
- Factors affecting spatial resolution:
- Field of view: increases in FOV decrease spatial resolution.
- Pixel size: smaller pixel size increases spatial resolution.
- Magnification: increasing magnification decreases spatial resolution.
- Pitch: higher pitch decreases spatial resolution.
- Slice thickness: larger slice thickness decreases spatial resolution.
Contrast Resolution
- Contrast resolution is the ability to differentiate a structure that varies only slightly in density from its surroundings.
- CT is superior to all other clinical modalities in its contrast resolution.
- Objects with a 0.25-0.5% contrast variation can be distinguished on CT images.
Temporal Resolution
- Temporal resolution refers to a system's ability to rapidly acquire data.
- Controlled by: gantry rotation speed, number of detector channels in the system.
- High temporal resolution is important when imaging moving structures (e.g., heart) and for studies dependent on dynamic flow (e.g., CT angiography).
Quality Assurance
- ACR CT accreditation phantom consists of four modules that can be used to examine a broad range of scanner parameters.
- QA tests include:
- Contrast resolution QA: assesses low-contrast resolution using a phantom with objects of variable sizes with a small difference in density.
- Slice thickness and laser light accuracy QA: measures slice thickness using a phantom with known measurements and evaluates laser light from the gantry.
- CT number QA: tests the average CT number of water (should be 0 ± 3) and air (-1000 ± 5).
- Noise and uniformity QA: measures noise using the standard deviation of CT numbers within a single ROI and uniformity by placing several ROIs within the phantom.
- Linearity QA: measures linearity using a phantom containing a variety of objects with known densities.
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Description
Assess your understanding of CT image quality, including spatial resolution, contrast resolution, temporal resolution, CT number accuracy, and quality assurance.
