Contrast media

CT contrast media contain iodinated compounds that are relatively radiodense. In central nervous system (CNS) imaging, MR contrast media are chelates of gadolinium. There is normal enhancement of flowing blood and structures normally lacking a blood-brain barrier (BBB). Diseases that cause disruption of the BBB allow contrast media to enter the extracellular space, producing tissue enhancement on imaging (Box 4.2).

Life-threatening allergic reactions to injected contrast media are now very rare. The risk of exacerbating renal impairment with injudicious use of iodinated contrast media has long been recognized. However, an association has recently been recognized between nephrogenic systemic fibrosis and previous administration of gadolinium-based contrast media to patients in severe renal failure. The

Box 4.2 Normal structures on brain MRI that show contrast enhancement need for contrast media of any sort should be carefully considered in patients with renal impairment.

Radiation exposure_

X-ray based imaging modalities should be avoided when not strictly necessary. Sometimes the information required can be obtained by other means, namely MRI, ultrasound, or in some circumstances a more experienced clinical opinion. This particularly applies in children, young adults and women of reproductive age. In practice, the benefits of imaging almost always outweigh dose considerations in neuroimaging, particularly in emergency situations.

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  • Category: Nervous diseases