CT Image Quality: Spatial Resolution Quiz and Flashcards

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Questions and Answers

What is the effect of increasing the field of view on spatial resolution?

It decreases spatial resolution

What is the relationship between pixel size and spatial resolution?

Smaller pixel size results in higher spatial resolution

What is the effect of increasing magnification on spatial resolution?

It decreases spatial resolution

What is the effect of increasing pitch on spatial resolution?

It decreases spatial resolution Signup and view all the answers

What is the effect of increasing slice thickness on spatial resolution?

It decreases spatial resolution Signup and view all the answers

What is contrast resolution dependent on?

Ability to differentiate structures with slight density variations Signup and view all the answers

What is the limitation of screen-film radiography in terms of contrast resolution?

Objects must have at least a 5-10% difference in contrast Signup and view all the answers

What is temporal resolution controlled by?

Gantry rotation speed and detector channels Signup and view all the answers

What is the importance of high temporal resolution in CT imaging?

It is important for imaging moving structures and dynamic flow studies Signup and view all the answers

What is the purpose of the ACR CT accreditation phantom?

To examine a broad range of scanner parameters Signup and view all the answers

What is the primary factor that determines the usefulness of a CT image?

Image quality Signup and view all the answers

What is the unit of measurement for spatial frequency in CT scanners?

Line pairs per centimeter (lp/cm) Signup and view all the answers

Which method is used to graphically represent a system's performance in terms of spatial resolution?

Modulation transfer function (MTF) Signup and view all the answers

What is the ability to distinguish between object or structures that differ in density?

Spatial resolution Signup and view all the answers

What is the purpose of measuring spatial resolution in CT imaging?

To provide an accurate diagnosis Signup and view all the answers

What is the relationship between spatial resolution and line pair phantom?

Spatial resolution is directly measured using a line pair phantom Signup and view all the answers

What is the primary factor that affects the ability of a CT scanner to distinguish between object or structures that differ in density?

Spatial resolution Signup and view all the answers

What is the term used to describe the number of line pairs per unit length?

Spatial frequency Signup and view all the answers

Which of the following is a measure of CT image quality?

All of the above Signup and view all the answers

What is the purpose of measuring CT image quality?

To provide an accurate diagnosis Signup and view all the answers

What is the purpose of the phantom in the Slice Thickness QA?

To include ramp or step-wedge of known measurements Signup and view all the answers

How often is the Noise and Uniformity QA performed?

Weekly Signup and view all the answers

What is the acceptable range of CT numbers for air in the CT Number QA?

-1000 ± 5 Signup and view all the answers

What is the purpose of the phantom in the Contrast Resolution QA?

To contain objects of variable sizes with a small difference in density from their surroundings Signup and view all the answers

How often is the LinearITY QA performed?

Semiannually Signup and view all the answers

What is the purpose of the ROI in the Noise and Uniformity QA?

To obtain the standard deviation of the CT numbers Signup and view all the answers

What is the purpose of the phantom in the CT Number QA?

To test the average CT number of water and air Signup and view all the answers

How often is the Slice Thickness and Laser Light Accuracy QA performed?

Semiannually Signup and view all the answers

What is the acceptable range of CT numbers for water in the CT Number QA?

0 ± 3 Signup and view all the answers

What is the purpose of the phantom in the Linearity QA?

To contain a variety of objects with known densities Signup and view all the answers

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.