Medical Imaging Glossary

A

ALARA

An acronym for "As Low As Reasonably Achievable." The guiding safety principle in radiology, meaning to use the lowest possible radiation dose that still produces a diagnostic-quality image.

Angiography

An imaging technique used to visualize the inside of blood vessels and organs, typically performed with contrast agents in CT, MRI, or Fluoroscopy.

Artifact

A feature seen on a medical image that is not present in the real-world object. Artifacts are caused by the physics of the imaging process, patient motion, or the presence of metal, and can degrade image quality.

C

Contrast Agent

A substance used to enhance the visibility of internal structures. Examples include iodine for CT, gadolinium for MRI, and barium for fluoroscopy.

CT (Computed Tomography)

An imaging modality that uses a rotating X-ray source and computer processing to create detailed, cross-sectional images of the body.

D

DICOM

An acronym for "Digital Imaging and Communications in Medicine." The international standard file format for storing and transmitting medical images and their associated metadata.

Doppler

A type of ultrasound that uses the Doppler effect to measure the speed and direction of blood flow within vessels.

DWI (Diffusion Weighted Imaging)

An MRI sequence that measures the random motion (diffusion) of water molecules. It is highly sensitive for detecting acute strokes.

E

Effective Dose

A calculated measure of radiation dose, measured in Sieverts (Sv), that accounts for the type of radiation and the sensitivity of the specific organs irradiated. It is the best measure of overall long-term health risk.

F

FLAIR (Fluid Attenuated Inversion Recovery)

An MRI sequence that is similar to T2 but suppresses the bright signal from normal fluid (like CSF), making abnormalities near fluid-filled spaces easier to see.

Fluoroscopy

An imaging technique that uses a continuous, low-dose X-ray beam to create a real-time "video" of internal structures, often used to guide procedures.

G

Gantry

The large, doughnut-shaped part of a CT or MRI scanner that houses the imaging equipment and that the patient slides into.

H

Hounsfield Units (HU)

The standardized numerical scale used in CT to represent the density of different tissues. Water is 0 HU, bone is high (e.g., +1000 HU), and air is low (-1000 HU).

Hyperdense / Hyperintense

Terms used to describe an area that appears brighter than the surrounding tissue on a CT scan (hyperdense) or an MRI scan (hyperintense).

I

Interventional Radiology (IR)

A subspecialty of radiology where physicians perform minimally invasive, image-guided procedures to diagnose and treat diseases.

L

Lesion

A general term for any abnormal area of tissue in the body, such as a tumor, cyst, or abscess. It does not imply cancer.

M

Modality

A specific type of medical imaging equipment (e.g., CT, MRI, Ultrasound).

MRI (Magnetic Resonance Imaging)

An imaging modality that uses a powerful magnetic field and radio waves to create detailed images, especially of soft tissues, without using ionizing radiation.

N

Nuclear Medicine

A branch of medical imaging that uses small amounts of radioactive materials (radiotracers) to diagnose and treat diseases by visualizing physiological function rather than anatomy.

P

PACS (Picture Archiving and Communication System)

The IT system used in hospitals to store, retrieve, distribute, and display medical images. It is the digital equivalent of a film library.

PET (Positron Emission Tomography)

A nuclear medicine technique that produces 3D images of metabolic activity in the body. It is widely used in oncology to detect cancer.

R

Radiolucent / Radiopaque

Terms describing how materials appear on an X-ray. Radiolucent materials (like air) allow X-rays to pass through easily and appear dark. Radiopaque materials (like bone or barium) block X-rays and appear bright.

RIS (Radiology Information System)

The software system used to manage the administrative and workflow aspects of a radiology department, including patient scheduling, exam ordering, and reporting.

S

Sievert (Sv)

The standard unit of effective dose, used to measure the long-term health risk from ionizing radiation. Medical doses are typically measured in millisieverts (mSv).

STAT

From the Latin "statim," meaning "immediately." An order for a medical imaging exam that signifies a critical emergency requiring immediate attention.

T

T1-Weighted

A fundamental MRI sequence where fat appears bright and water appears dark. It is excellent for visualizing normal anatomy.

T2-Weighted

A fundamental MRI sequence where both fat and water appear bright. It is very sensitive for detecting pathology, as most diseases involve an increase in water content.

Tomosynthesis

An advanced imaging technique, also known as 3D mammography, where an X-ray tube moves in an arc to create multiple thin "slices" of the breast, reducing the problem of overlapping tissue.

U

Ultrasound

An imaging modality that uses high-frequency sound waves and their echoes to create real-time images of the body's organs and tissues.

V

Voxel

A "volumetric pixel." It is the 3D equivalent of a pixel, representing a single point in a 3D grid of image data.