MRAD 3510 Module 3: Scan Parameters and Image Quality

Flashcards covering key vocabulary terms and concepts from Module 3: Scan Parameters and Image Quality in MRAD 3510, focusing on CT image quality elements, scan parameters, and methods for improvement.

SFOV (Scan Field of View)

The circular area within the gantry where raw data is acquired, measured from the isocenter.

Out of Field Artifact

An artifact that can occur when anatomy lies outside the SFOV, as data is not collected for that area.

DFOV (Display Field of View)

Determines how much of the acquired data is selected to be displayed; it can be smaller than or equal to the SFOV, but never larger.

Scan Parameters Affecting Image Quality

These include mAs, kVp, slice thickness, FOV, reconstruction algorithms, pitch, and scan geometry.

mAs

The product of mA (milliamperage) and scan time, which is how long it takes for the X-ray tube to make one full rotation.

Image Quality

Assessed by how well an image represents the scanned object, typically evaluated using spatial resolution, low-contrast resolution, and temporal resolution.

Spatial Resolution

Also known as detail resolution or high contrast resolution, it is the ability to define small, closely placed objects as distinct and separate.

Low-Contrast Resolution

The ability of the system to clearly differentiate objects with only slightly different densities from their background.

Pixel Size and Spatial Resolution

Pixel size is calculated as DFOV/matrix. Smaller pixels decrease the chance of volume averaging, leading to better spatial resolution.

Volume Averaging

A phenomenon where a single pixel or voxel represents an average of all the different tissue densities within it, potentially blurring fine details. Smaller pixels and thinner slices reduce this.

Slice Thickness (Spatial Resolution)

Thinner slices decrease the chances for volume averaging by representing less tissue within each pixel, thus improving spatial resolution.

Reconstruction Algorithms (Spatial Resolution)

Can be applied to make image data appear more smooth or sharp, depending on the desired outcome for different body areas.

Methods to Improve Spatial Resolution

Utilizing the smallest possible DFOV, thinnest acquisition width, noise-reducing or edge-enhancing reconstruction algorithms, and reduced pitch.

Noise (Image Quality)

Undesirable fluctuation of pixel values, primarily caused by quantum mottle or an insufficient number of photons.

Quantum Mottle

A type of imaging noise caused by an insufficient number of photons reaching the detector, leading to a grainy appearance and an inverse relationship with noise (less photons, more noise).

SNR (Signal-to-Noise Ratio)

Represents the number of photons detected per pixel; higher SNR generally indicates better image quality with less noise.

Methods to Improve Low Contrast Resolution

Increasing mAs/dose (decreases noise), increasing pixel size (more photons per pixel, less noise), and increasing slice thickness (more photons, better SNR, less noise).

Uncoupling Effect

A complex relationship observed with digital technology where image quality is not directly proportional to radiation dose, meaning high mA or kVp can still result in a good-looking image despite potentially higher dose.