The ability to non-invasively image the arteries and veins in the body with MRI has improved tremendously over the past 20 years. The initial techniques employed novel MR sequences that were sensitive to flowing blood while suppressing the stationary background tissue. The technique that has enjoyed the greatest clinical acceptance is called time-of-flight MR angiography. With this technique fresh blood flows into the vessels carrying with it new signal. This allows us to see the arteries and veins as bright objects with the background tissue relatively dark. Maximum intensity projections can display this complex anatomy in 3-D. With this technique investigators have been able to generate MR angiograms that rival those obtained from invasively placing a catheter into the artery and injecting contrast. It is now possible to show very small arteries in the brain on the order of 500µ in diameter that are the common cause of strokes. In the near future we may be able to follow the effectiveness of lipid lowering therapies by watching the response of the small brain arteries. We potentially can individualize the treatment of high cholesterol by measuring whether the stenosis in the arteries of the brain regresses.

Recently, contrast enhanced MR angiography has shown great promise. This technique relies on capturing the first pass of contrast in the arteries following intravenous administration. The result has been MR angiograms that are faster and less sensitive to patient motion artifact. These have greatly improved the reliability of MR angiography and increased its clinical acceptance. Time resolved imaging of the arteries allows us to watch the pass of gadolinium through the arteries in the legs. This has proven to be of great benefit because the flow in the arteries is frequently very asymmetric.

In addition to looking for stenosis of the patent lumen in the arteries, some investigators are now evaluating the plaque that has built up in the walls of the arteries and caused the stenosis. Detailed evaluation of the various carotid plaque components/ in vivo/ is now possible utilizing modern 3T MR combined with dedicated surface coils. We have shown good agreement between this /in vivo/ 3T MR plaque characterization and histological evaluation of the plaque after it's been surgically removed. New prospective studies are suggesting that plaque components may be a better predictor of who will ultimately develop a stroke then simple measurement of the carotid artery lumen stenosis. They also allow us to monitor the effect of new drug therapies to lower lipid and hopefully shrink the plaque that is causing the arterial narrowing. In the future we may be able to detect whether a new therapy is working and switch to a different drug to shrink plaque when the older therapy is ineffective.

Throughout its history MR angiography has added value to the work up of patient's with suspected stenosis, first by replacing invasive angiography and later by yielding new information about the plaque causing the stenosis that was unknown in the past. These improvements allow us to monitor therapy and individualize the patient's treatment.