MRI Scan Glossary: Medical Terms Explained

MRI reports and medical literature are full of specialised terminology that can leave you baffled. This MRI glossary translates the most common terms into plain language — from scanner technology to report findings.

Scanner and Technology Terms

Axial

An image plane that slices the body horizontally, as if viewed from above. Also called "transverse." Think of it as looking at a cross-section of a loaf of bread.

Bore

The cylindrical opening of the MRI scanner that you lie inside. Standard bore diameter is roughly 60cm; wide-bore scanners are 70cm.

Coil

A device placed on or around the body part being scanned to send and receive radio signals. Different coils for different areas (head coil, knee coil, spine coil). The coil is like an antenna that picks up the signals your body emits.

Contrast agent (gadolinium)

A substance injected into a vein to make certain tissues brighter on MRI images. The most common MRI contrast is gadolinium.

Coronal

An image plane that slices the body vertically from front to back — as if you're looking at someone face-on.

Diffusion-weighted imaging (DWI)

A specialised sequence that measures water molecule movement in tissue. Restricted diffusion (bright on DWI) is the hallmark of acute stroke and is also useful for characterising tumours.

FLAIR (Fluid-Attenuated Inversion Recovery)

A sequence that suppresses the signal from cerebrospinal fluid (brain fluid appears dark). Makes small brain lesions near the ventricles much easier to spot. Standard in brain MRI protocols.

Gadolinium

A rare-earth metal used as the basis for MRI contrast agents. Enhances certain tissues on T1-weighted images. See our gadolinium guide.

Gradient coils

Electromagnetic coils that create varying magnetic fields for spatial encoding — allowing the scanner to map where signals come from. They're responsible for the loud noises during scanning.

MR Angiography (MRA)

An MRI technique specifically for imaging blood vessels, often without contrast injection. Used to screen for aneurysms, stenosis, and vascular malformations.

MR Conditional

A safety label meaning an implant can be safely scanned under specific conditions (e.g., only at 1.5T, only with certain settings). Most modern implants are MR Conditional. See our implants guide.

MR Safe

An implant that poses no known hazards in any MRI environment (contains no metal whatsoever).

MR Unsafe

An implant that poses unacceptable risks and cannot be scanned. Includes some older pacemakers and certain intracranial aneurysm clips.

MRCP (Magnetic Resonance Cholangiopancreatography)

An MRI technique that images bile ducts and the pancreatic duct without contrast. Used for gallstones, strictures, and biliary conditions. See our MRCP scan.

Multiparametric MRI (mpMRI)

An MRI protocol combining multiple sequence types (T2, DWI, dynamic contrast enhancement) in one examination. Most commonly used for prostate imaging — it's the recommended first-line investigation for suspected prostate cancer.

SAR (Specific Absorption Rate)

A measure of the rate at which radiofrequency energy is absorbed by the body during MRI. Monitored automatically to keep tissue heating within safe limits.

Sagittal

An image plane that slices the body vertically from side to side — as if looking at someone from the side.

Sequence

A specific combination of radiofrequency pulses and gradient settings used to generate images with particular characteristics. Each sequence takes 2-7 minutes and highlights different tissue properties.

STIR (Short Tau Inversion Recovery)

A sequence that suppresses fat signal, making fluid and oedema stand out. Widely used in musculoskeletal imaging for detecting bone marrow oedema, stress fractures, and soft tissue inflammation.

T1-weighted

A sequence where fat appears bright (white) and water appears dark. Excellent for showing anatomical structure. Enhanced by gadolinium contrast.

T2-weighted

A sequence where water and fluid appear bright (white) and fat appears darker grey. Excellent for detecting oedema, inflammation, cysts, and many types of pathology.

Tesla (T)

The unit of magnetic field strength. Clinical scanners operate at 1.5T or 3T — that's 30,000-60,000 times stronger than Earth's magnetic field. Higher Tesla = higher resolution images.

Report and Findings Terms

Artefact

A distortion in the image caused by movement, metal, or technical factors. Not a real finding — it's a limitation of the image. Can sometimes obscure or mimic pathology.

Atrophy

Shrinkage or wasting of tissue. Brain atrophy (loss of brain volume) is a normal part of ageing. Accelerated or asymmetric atrophy may indicate disease (e.g., Alzheimer's, frontotemporal dementia).

Benign

Not cancerous. A benign finding doesn't need treatment in most cases.

Cyst

A fluid-filled sac. Almost always benign. Extremely common in kidneys (found in ~25% of adults over 50), brain (pineal cysts in ~10%), liver, and ovaries.

Degenerative changes

Age-related wear and tear. Very common in the spine and joints, often present without any symptoms. Think of them as grey hairs for your joints.

Disc bulge / protrusion / herniation

Different degrees of spinal disc displacement. A bulge is broad and mild; a protrusion is more focal; a herniation is when disc material extends significantly. Only clinically significant if it presses on a nerve. See our results guide.

Effusion

Excess fluid inside a joint or body cavity. Indicates inflammation, injury, or arthritis.

Enhancement

When tissue takes up gadolinium contrast and appears brighter on post-contrast images. Indicates increased blood flow or breakdown of normal barriers (e.g., blood-brain barrier). May indicate tumour, inflammation, or infection.

Haemangioma

A benign growth made of blood vessels. Very common in the liver (found in ~5% of adults) and vertebral bodies. Almost always harmless and incidental.

Hyperintense / high signal

Appears brighter than surrounding tissue on the image.

Hypointense / low signal

Appears darker than surrounding tissue.

Incidental finding

Something found unexpectedly during a scan done for a different reason. Most are benign. The radiologist will clearly state if follow-up is needed.

Indeterminate

Can't be confidently characterised from this scan alone. Doesn't mean cancer — means more information is needed.

Lesion

A general term for any area of abnormal tissue. Does not imply cancer. A lesion can be a cyst, a scar, an area of inflammation, a benign growth, or a malignant tumour. Context determines significance.

Lipoma

A benign fatty lump. Very common and harmless. Has a distinctive appearance on MRI (follows fat signal on all sequences).

Malignant

Cancerous. Capable of invading surrounding tissues and spreading (metastasising) to other parts of the body.

Mass

An abnormal lump or growth. Can be benign or malignant. Further investigation (contrast MRI, biopsy, or follow-up scan) may be needed to determine its nature.

Oedema

Swelling caused by excess fluid in tissue. Appears bright on T2 and STIR sequences. Can indicate inflammation, injury, infection, or bone stress reaction.

Signal abnormality

An area that looks different from expected. May indicate pathology or a harmless normal variant.

Stenosis

Narrowing. Common in the spine (spinal stenosis — narrowing of the spinal canal) and blood vessels (arterial stenosis). Graded as mild, moderate, or severe.

Unremarkable

Normal. Nothing abnormal found. Possibly the most reassuring word in radiology.

Spinal Terminology

Annular tear / fissure

A tear in the outer ring (annulus fibrosus) of a spinal disc. Can cause localised back pain and may precede disc herniation. Very common on MRI in adults over 30.

Cauda equina

The bundle of nerves at the base of the spinal cord (below the L1-L2 vertebrae). Cauda equina syndrome (compression of these nerves causing bladder/bowel dysfunction) is a surgical emergency.

Desiccation

Loss of water content in a spinal disc. The disc appears dark on T2 images (healthy discs are bright with water). A normal part of ageing — present in 37% of asymptomatic 20-year-olds.

Foraminal stenosis

Narrowing of the bony openings (foramina) where spinal nerves exit. Can compress nerves, causing arm or leg pain, numbness, or weakness.

Modic changes

Signal changes in the vertebral bone next to a degenerated disc. Type 1 (inflammatory — may correlate with pain), Type 2 (fatty — usually stable), Type 3 (sclerotic — dense bone).

Spondylosis

General umbrella term for degenerative changes in the spine: disc degeneration, bone spurs (osteophytes), facet joint wear. Extremely common and often asymptomatic.

Spondylolisthesis

One vertebra slipping forward relative to the one below it. Graded 1-4 based on percentage of slippage. Grade 1 (up to 25%) is common and often incidental.

For help interpreting your specific report, see our guides on how to read your MRI report and understanding your MRI results.