Background
Magnetic resonance imaging (MRI) is a medical diagnostic
technique that creates images of internal body structures using the principle
of nuclear magnetic resonance. MRI scans are performed within a strong,
rotating magnetic field. Thus, it can generate thin-section images of any part
of the human body, from any angle and direction. The diagnostic
performance of MRI is often improved by an intra-articular injection of a
contrast medium, which makes derangements and lesions more conspicuous by
outlining the joint space.1 This is referred to as magnetic
resonance arthrography (MRa), which has become popular in recent years.2
The diagnostic accuracy of MRa may exceed that of conventional MRI because of
the intra-articular structures are better visualized when separated via
capsular distension.
Description
MRa involves the intra-articular injection of a contrast
medium such as gadolinium. Unlike other contrast agents, gadolinium itself does
not produce an MRI signal. Instead, it acts by shortening the T1 and T2
relaxation times of the tissues into which it extravasates.2 Most
commonly, a mixture of saline, iodinated contrast agent, lidocaine and
gadolinium is injected into the joint using fluoroscopic guidance. After the
contrast agent is injected, the site is sealed, and the patient may be asked to
move the joint to distribute the contrast. The purpose of contrast agents is to
highlight details of the structures under study by making them opaque.
A normal MRa shows proper placement of the contrast medium
throughout the joint, cartilage and ligaments. In an abnormal MRa, the entire
lining of the joint becomes opaque. An abnormal MRa may indicate degenerative changes, a cyst or
other mass, joint dislocation, ruptures or tears in the ligaments and other
conditions.
