Noninvasive arterial imaging

Fatty plaques within the carotid artery build up over time, leading to a risk of stroke or other transient ischemic attack. To reduce the possibility of stroke, patients with substantial blockages (70 percent or more stenosis) of the carotid artery traditionally have been eligible for a risky surgery, called endarterectomy, to remove the plaque. Some patients with lower amounts of blockage (50 to 69 percent stenoses) also can be eligible for this procedure. Unfortunately, determining the amount of stenosis in an artery also requires an invasive, risky and expensive procedure: intra-arterial angiography.

Since the mid-1990s, imaging techniques such as computed tomographic angiography, Doppler ultrasound, and magnetic resonance and contrast-enhanced magnetic resonance angiography have emerged as candidates to replace intra-arterial angiography. Each method is noninvasive and, therefore, much less risky. However, according to Joanna M. Wardlaw of Western General Hospital in Edinburgh and her colleagues at the Universities of Oxford and Leeds, all in the UK, there is scant evidence that any of these alternatives is ready to replace intra-arterial angiography outright.

In a meta-analysis of nearly 25 years of imaging studies, Wardlaw and her colleagues located only 41 papers with acceptable studies to consider. Most of the 631 studies that they excluded had very small patient populations, included only some noninvasive techniques, or possibly or definitely used suboptimal study designs. They concluded that — used cautiously — any of the noninvasive techniques could replace intra-arterial angiography, especially to image 70 to 99 percent stenoses, but not before more and better studies are conducted to prove their value.

They recommend that future studies ensure consistent double-blinding efforts; include patients’ groups that are more relevant than those in previous studies; use prospective recruitment techniques; use standard, approved patient-selection processes and describe them adequately; provide analysis on a per-patient rather than per-artery basis; report the ratio of symptomatic to asymptomatic arteries in each patient; and ensure clearly defined stenosis thresholds, rather than use rounding techniques or nonstandard ranges other than, for example, 70 to 99 percent. (The Lancet, May 6, 2006, pp. 1503-151.)