Receptor Exposure and Distortion in Digital Radiography

These flashcards cover key terms and concepts related to receptor exposure, distortion, and digital imaging in radiography.

Receptor Exposure

The amount of radiation passing through the patient and striking the image receptor.

Exposure Indicator (EI)

A manufacturer number that tells how much radiation has reached the receptor.

mAs

The controlling/main factor for receptor exposure; increases the number of photons in the beam.

kVp

Affects both beam quantity (number of photons) and beam quality (penetrability); follows the 15% rule.

Inverse Square Law

States that short SID increases receptor exposure while long SID decreases it due to beam divergence.

Collimation

The process of decreasing field size to reduce scatter and enhance receptor exposure.

Anode Heel Effect

The phenomenon where smaller anode angles decrease exposure due to absorption by the anode.

Filtration

Designed to reduce the number of low-energy photons in the primary beam at the cost of reducing receptor exposure.

Scatter Absorption

Affects receptor exposure; smaller grid ratios allow more photons to reach the receptor.

X-ray Attenuation

The reduction of radiation intensity as it passes through matter, significant in varying patient sizes.

Shape Distortion

Unwanted elongation or shortening of anatomy compared to its original size in a radiographic image.

Size Distortion (Magnification)

Describes the size difference between actual anatomy and its representation in the image.

Source to Image Distance (SID)

The distance from the x-ray tube to the image receptor; decreasing SID increases magnification.

Object to Image Distance (OID)

The distance between the anatomy and the image receptor; decreasing OID decreases magnification.

Source to Object Distance (SOD)

Distance from the x-ray tube to the object; increasing SOD decreases magnification.

Histogram

A graphic representation of exposures/pixel values recorded by the image receptor.

Values of Interest (VOI)

The exposure values used for processing the image for viewing, excluding irrelevant areas.

Lookup Table (LUT)

Adjusts the image's brightness and contrast to the desired levels using a mathematical process.

Image Contrast

The difference in brightness between adjacent areas on an image.

Spatial Resolution

The ability to distinguish between two adjacent objects that are close together; also known as sharpness of detail.

X-ray Grid Function

To absorb scatter radiation before it reaches the image receptor, thereby improving image contrast.

Grid Ratio

The ratio of the height of the lead strips to the distance between them.

Image Noise

Random fluctuations in optical density or brightness on the image, which can obscure detail.

Quantum Mottle

A type of image noise caused by insufficient number of x-ray photons reaching the image receptor, resulting in a grainy appearance.

Detective Quantum Efficiency (DQE)

A measure of the effectiveness of an image receptor in converting the x-ray input signal into a useful output image; higher DQE means less patient dose.

Pixel Pitch

The distance between the centers of two adjacent pixels; smaller pixel pitch generally leads to higher spatial resolution.

Focal Spot Size

The area on the anode target from which x-rays are emitted; a smaller focal spot size generally produces a sharper image (higher spatial resolution).

Beam Quantity

The total number of x-ray photons in the beam.

Beam Quality

The penetrating power of the x-ray beam.

Scatter Radiation

X-ray photons that have been deflected from their original path after interacting with matter, degrading image contrast.

Magnification Factor

The ratio of image size to object size, indicating how much an object is magnified in a radiographic image.

Window Level

A post-processing control that adjusts the brightness of the image (often linked to the center of the LUT).

Window Width

A post-processing control that adjusts the contrast of the image (often linked to the range of the LUT).

15% Rule

A radiographic principle stating that increasing kVp by 15% will double receptor exposure, equivalent to doubling mAs. Conversely, decreasing kVp by 15% will halve receptor exposure.

Foreshortening

A type of shape distortion where the anatomical part appears shorter than its actual size due to angular misalignment of the anatomical part or the image receptor relative to the central ray.

Elongation

A type of shape distortion where the anatomical part appears longer than its actual size due to angular misalignment of the x-ray tube or the image receptor relative to the anatomical part.

Computed Radiography (CR)

A digital imaging technique that uses a photostimulable phosphor plate (PSP) to capture the latent image, which is then 'read' by a laser scanner to produce a digital image.

Direct Digital Radiography (DR)

A digital imaging technique that directly converts x-ray photons into an electrical signal using a flat panel detector, providing immediate image display.

Exposure Latitude (Digital Imaging)

The range of x-ray exposures (mAs) that can produce an acceptable diagnostic image with digital receptors, generally wider than film-screen systems due to post-processing capabilities.

Automatic Exposure Control (AEC)

A system used to automatically terminate the x-ray exposure once a sufficient amount of radiation has reached the image receptor, ensuring consistent receptor exposure.

Signal-to-Noise Ratio (SNR)

A measure comparing the level of a desired signal to the level of background noise; a higher SNR indicates a clearer image with less noise and better diagnostic quality.

Pixel Density

The number of pixels per unit area in an image; higher pixel density contributes to higher spatial resolution.

Modulation Transfer Function (MTF)

A measure of the ability of an imaging system to transfer spatial frequencies from the object to the image; represents a system's overall spatial resolution.

Dynamic Range (Digital Imaging)

The range of x-ray intensities that a digital image receptor can detect and display; digital systems typically have a wider dynamic range than film-screen systems.

Exposure Index (EI) Target Range

The acceptable range of Exposure Indicator (EI) values recommended by manufacturers for optimal image quality and patient dose.

Look-Up Table (LUT) Application

The process by which raw pixel data is transformed to adjust image brightness and contrast, ensuring consistent image appearance regardless of exposure variations.

Display Monitor Resolution

The number of pixels a display monitor can show, directly affecting the perceived spatial resolution of a digital image.

Exposure Field Recognition

The ability of digital imaging software to identify the relevant exposed area on the image receptor, excluding unexposed regions, crucial for accurate histogram analysis.

Grayscale Bit Depth

The number of shades of gray that an imaging system can reproduce, with a higher bit depth allowing for more subtle distinctions in tissue densities.

Photodetector

A device used in indirect DR systems (and CR readers) that converts light photons into electrical signals.

Thin-Film Transistor (TFT) array

An array of detector elements (DELs) used in flat panel detectors (both direct and indirect DR) to collect and read out the electrical charges that represent the image.

Fill Factor

The percentage of the pixel area in a flat panel detector that is sensitive to x-rays; a higher fill factor generally leads to better image quality but can be limited by the space taken by electronics.