Key Concepts in Digital Imaging and Radiography

Bit

A bit is the smallest unit of digital data. It can only be a 0 or a 1.

Byte

A byte is a group of 8 bits. It's used to store one character or piece of data.

Computed Radiography (CR)

A digital imaging system that uses a cassette with a photostimulable storage phosphor (PSP) plate to capture X-ray images. The plate is scanned by a laser to create a digital image.

Digital Radiography (DR)

A digital system where images are captured directly onto a flat panel detector—no cassette needed. It's faster than CR.

Direct Conversion

A DR method that converts X-rays straight into electrical signals using a material like amorphous selenium, skipping the light conversion step.

Indirect Conversion

A DR method that first turns X-rays into light using a scintillator, and then the light is converted to electrical signals by photodiodes.

Detective Quantum Efficiency (DQE)

A measure of how well a detector captures useful image data with the least amount of noise. A higher DQE means better image quality with less radiation.

Deviation Index (DI)

A number that tells how close the exposure level is to the proper amount for the exam. It helps technologists adjust future exposures.

Edge Enhancement

A type of image processing that makes edges in an image look sharper. It helps outline structures but can sometimes create false details.

Flat Panel Detector

A device in DR systems that captures and turns X-ray signals into digital images. It's like a digital version of a film screen.

Grayscale Bit-Depth

Refers to how many shades of gray a system can display. More bits mean more shades and better detail.

High-Pass Filtering

An image processing method that sharpens edges and makes detail stand out. Also called edge enhancement.

Low-Pass Filtering

An image processing method that smooths the image by reducing noise. It may make the image look softer or blur fine details.

Histogram

A graph that shows how many pixels in an image have certain brightness values. It helps the computer adjust image brightness and contrast.

Look-Up Table (LUT)

A preset guide the computer uses to convert raw image data into a final image with the right brightness and contrast.

Matrix

The grid of rows and columns that makes up a digital image. Each square in the matrix is a pixel.

Photostimulable Storage Phosphor Imaging Plate (PSP)

Used in CR systems, it stores the X-ray image. When scanned with a laser, it gives off light to create a digital image.

Pixel

Short for 'picture element,' it's the smallest piece of a digital image. Each pixel holds one shade of gray.

Pixel Pitch

The distance from the center of one pixel to the center of the next. Smaller pixel pitch = better image detail.

Rescaling

A process where the computer adjusts image brightness and contrast to match normal levels, even if the exposure was off.

Signal-to-Noise Ratio (SNR)

Compares useful image data (signal) to background fuzziness (noise). A high SNR means a clearer image.

Spatial Resolution

How well an image shows small details. Higher spatial resolution = sharper image.

Windowing

Adjusting the brightness and contrast of an image using 'window level' (for brightness) and 'window width' (for contrast).