Digital Imaging Pre-processing and Characteristics

Vocabulary flashcards defining key terminology related to computed radiography, digital pre-processing, matrix characteristics, spatial resolution, and signal sampling.

Photostimulable Phosphor Plate

A reusable imaging plate coated with photostimulable phosphors that is exposed to X-rays in computed radiography systems.

Latent Image Formation

The process where X-rays interact with photostimulable phosphors on an imaging plate, trapping electrons in higher energy states to store an image.

Stimulated Emission

The process in CR image reading where laser energy excites trapped electrons, causing them to return to their ground state and release energy as light.

Photomultiplier Tube (PMT)

A component in a CR image reader that collects light emitted during laser scanning and amplifies the analog signal.

Pre-processing

The initial stage of digital image processing that corrects flaws in raw digital data introduced during image acquisition to optimize the image for diagnostic interpretation.

Post-processing

The stage of digital radiography processing where pre-processed image data is manipulated to enhance its appearance or extract specific information.

Exposure Field Recognition

A pre-processing step that identifies the clinically useful area of an image on the imaging plate and eliminates signals from outside the collimated field.

Data Clipping

A histogram analysis process where software identifies and excludes pixel data representing exposures significantly below or far above the diagnostic imaging range.

Values of Interest (VOI)

The range of relevant exposure data in a histogram determined for a specific body part.

Look-Up Table (LUT)

A table containing appropriate contrast settings and algebraic conversion equations for specific body parts, used to transform input pixel values to output display values.

Grayscale Analysis

The process of transforming input digital data values into display output values representing shades of gray using a look-up table.

Matrix

A two-dimensional grid of picture elements (pixels) in which a digital image is recorded.

Pixel

A single picture element representing a numerical value corresponding to a specific area or volume of tissue.

Field of View (FOV)

The anatomical area or volume of tissue being imaged.

Bit Depth

The number of bits used to represent each pixel's value, which determines the precision of analog-to-digital conversion and the number of displayable shades of gray.

Pixel Density

The number of pixels per unit area, where higher density results in improved spatial resolution.

Pixel Pitch

The distance measured from the center of one pixel to the center of an adjacent pixel.

Spatial Resolution

The ability of an imaging system to distinguish between two or more closely spaced objects as separate entities.

Spatial Frequency

A measurement of anatomical detail sizes, often expressed in line pairs per millimeter ($\text{lp/mm}$), where small objects have high spatial frequencies and large objects have low spatial frequencies.

Modulation Transfer Function (MTF)

A measure of an imaging system's ability to display the contrast of anatomical objects of varying sizes, with values ranging from $0$ to $1.0$.

Sampling Frequency

The rate at which an analog signal is sampled during analog-to-digital conversion.

Sampling Pitch

The physical distance between sampling points during analog-to-digital conversion.

Aliasing

An artifact that occurs when the sampling frequency is too low, causing the digital waveform to inaccurately represent the true analog signal and resulting in detail loss.