Contrast Media

While MRI scans can yield excellent images in their own right, the visibility, detail and characterisation of structures can be enhanced by the appropriate use of contrast media. These media have been developed to take into account the special environment of the MRI scanner. These media can be classified into two groups.

Positive (T1) agents lead to amplification of signals from tissues. Gadolinium is the most well known agent in this class (Fig 1). Its value comes from its paramagnetic status; its nuclei align in a similar way to hydrogen ion nuclei in a magnetic field and increase the water-based signal, enhancing visibility of water-based tissues.

Negative (T2) contrast agents on the other hand lead to a reduced signal from some tissues. These media are iron oxide based. They are superparamagnetic, causing interference and reduced signal strength.

Learning bite

Contrast media can enhance the interpretation of images.

Other benefits

Other benefits of contrast media include:

• Angiography support
• Other dynamic studies
• Reduced scan times to acquire diagnostic images

Reactions

Gadolinium is usually considered to have a good safety profile but there have been reports of idiosyncratic reactions including skin lesions and joint pain.

Furthermore, there have been cases of nephrogenic systemic fibrosis reported after administration of gadolinium to patients with known renal disease [3].

Allergic and anaphylactic reactions are documented, but rare.