Improvements in arterial imaging aid stroke diagnosis

Forty-section scanners are the latest innovation in computed tomography (CT), having replaced the earliest CT instruments, spiral scanning, and four-section scanners.

"The technology has changed dramatically in the past 30 years. With early CT, only the brain, cerebrospinal fluid, air, and bone could be visualized; now there is amazing resolution and any desired plane can be displayed," Dr. Eggenberger explained.

The hardware has improved from the early 0.5-T magnets to the now-standard 1.5-T magnets; 3.0- and 4.5-T magnets are now also available.

The noninvasive CT angiography (CTA) and magnetic resonance angiography (MRA) also have improved substantially in the past 10 years, according to Dr. Eggenberger.

"Contrast-enhanced angiography is still the gold standard. This is important because certain lesions, such as those that may be visualized on the carotid, are now treatable in a number of ways, including endovascular techniques. Defining these lesions is even more important now than in the past," he said.

In contrast to the generation of MRA that was available in the late 1980s, in which vessel anatomy was displayed in two dimensions, flow now can be followed through the carotids and venous return watched. Flow physiology is now visible without the risks, such as stroke, associated with undergoing invasive contrast-enhanced angiography, Dr. Eggenberger explained.

The ability to see anatomic details has increased markedly. He pointed out that the ophthalmic artery can be visualized well, without contrast enhancement, with a 3.0-T magnet. Combining MRA and computer software allows even more detailed images that show blood flow through the brain over time.

"These techniques are user- and institution-dependent. To be able to take advantage of this technology, a radiologist and an institution that are familiar with the technology are necessary," he said.

Dr. Eggenberger demonstrated this noninvasive technology in a woman with a posterior inferior cerebellar artery aneurysm and a sixth-nerve palsy. She had had a stroke as the result of previous contrast-enhanced angiography. The CTA and MRA images were complementary; the MRA showed the pathology and surrounding structures over time and eliminated the need for repeated contrast-enhanced angiography. The technology allows the arteries to be evaluated three-dimensionally in the context of the surrounding tissue, which is helpful for planning surgery.

"The next step is looking at the stenoses in greater detail, such as the characteristics of the plaque within a stenotic lesion. These pathologies are treatable with endovascular techniques in more and more patients," he said.

Dr. Eggenberger said DWI is one of the most important recent advances. It can pick up areas of restricted diffusion, i.e., the sluggish movement around swollen cells that is part of the ischemic cascade following a cerebral insult when the sodium-potassium pump fails.

CT had been the procedure of choice to image a suspected acute stroke, but MRI now may be the more appropriate choice. In an article published in October 2004 in the Journal of the American Medical Association, 200 patients with acute focal stroke symptoms underwent imaging within 6 hours of symptom onset. The authors reported that CT and MRI are equal when it comes to demonstrating acute hemorrhage. However, for any hemorrhage beyond acute, MRI was far superior, Dr. Eggenberger reported.