Clinical evaluation of stenosis of the carotid bifurcation with magnetic resonance angiographic techniques

Modern techniques of medical imaging may produce astounding pictures of the body and its functions, but such images are not necessarily any better for purposes of diagnosis than those produced by more conventional techniques. The true value of any imaging technique can only be established by careful experimental evaluation. Just such an evaluation has been performed to compare two techniques of magnetic resonance imaging (MRI) with conventional angiography (X-ray of the blood vessels) for the examination of the carotid artery. Since angiography is an invasive technique requiring the insertion of catheter, MRI might be a significant improvement if its capabilities are also comparable. Stenosis, or narrowing, of the carotid artery carrying blood to the head is a major risk factor for stroke, and observation of this stenosis may lead to potentially preventive measures. The carotid bifurcations, where the carotid artery splits into the internal and external carotid arteries, were evaluated in 31 patients in whom carotid artery disease was suspected. The results provided by the established technique of invasive angiography were accepted as the correct diagnosis for purposes of comparison. Overall, the sensitivity of the MRI methods was 86 percent, meaning that 86 percent of the carotid artery abnormalities were actually detected by the MRI techniques. The specificity of the MRI methods was 92 percent, indicating that a negative indication by MRI will be right about 92 percent of the time. While these figures are close to the range which may make MRI suitable, it was also found that the errors which did occur happened because of difficulties experienced in the interpretation of the image, not the image quality. Furthermore, the physicians who read the images felt confident of their interpretations for 74 percent of the angiograms but for only 28 percent of the MR images. The MR images were apparently more difficult to read, and took 15 to 20 minutes, compared to the five minutes required to interpret a conventional angiogram. It would be advantageous to be able to use a noninvasive technique such as MRI for the evaluation of carotid stenosis, and, indeed, improvements in MRI technology may bring this to pass. At present, however, any adoption of the MRI technique for this purpose should be only with great care and strict adherence to evaluation methodology. (Consumer Summary produced by Reliance Medical Information, Inc.)