MR and MR-angiography in the assessment of steno-occlusive (atherosclerotic) disease of the carotid arteries in the cervical spine

This paper reassesses the role of MR and MRA in the diagnosis of steno-occlusive disease of the carotid arteries in the cervical spine, focusing on technical and clinical problems. 2D and 3D Time-of Flight (TOF) MRA techniques are more widely used than phase contrast methods (2D and 3D PC MRA) to investigate the carotid vessels in the neck. This is partly because TOF was commercially available before phase contrast and hers thus received wider clinical use. In addition, recent technical advances (e.g tilted optimized nonsaturating excitation -TONE- and multiple overlapping thin slab acquisition -MOTSA-) have given 2D and 3D TOF MRA excellent selective visualization of vessels in the cervical spine. Recent large clinical studies (e.g NASCET) have emphasized the importance of surgery to treat symptomatic patients with marked stenosis (79-99%) of the internal carotid artery and the need for effective preoperative screening. These studies found that the main factors affecting the surgeon's choice of operation include the degree of stenosis, the presence of ulcerated plaque and ''tandem'' lesions on the same vessel plane. Assessing the degree of internal carotid artery stenosis at the carotid bifurcation, MRA offers reliable information on arteries with normal calibre or mild stenosis without false negatives. However, MRA, especially the 2D TOF technique, does tend to overestimate the degree of stenosis. Recent studies have found MRA more reliable than echo-colour-Doppler methods in distinguishing occlusion from subocclusion, especially when both 2D and 3D TOF techniques are used. A major drawback in MRA investigation is the difficulty in characterizing the atherosclerotic plaque and detecting ulcerations, but technological advances (e.g, phased array surface coils) should soon resolve problems linked with spatial resolution, the signal/noise ratio and flow turbulence artifacts which currently prevent MR and MRA displaying ulcerated plaque. MRA is a panoramic technique visualizing not only the carotid bifurcation brat also the collateral blood supply from the circle of Willis, thus disclosing ''tandem'' lesions which some consider a major contraindication to surgery. Assessment of the origin of the epiaortic vessels is arduous, although quadrature coils, e.g. head and neck coils are already available to display the origin of the vessels from the aortic arch, carotid bifurcation and carotid siphons in one acquisition. The high negative predictive value and high sensitivity of the stenosis finding coupled with the non-invasiveness of MR and MRA in providing detailed information on brain structures make these techniques particularly suited to the pre-operative work-up in symptomatic patients with carotid stenosis. As screening techniques MR and MRA are more expensive than echo-colour-Doppler, but they depend less on the operator and offer a better overall display to select those patients who require target angiography with arterial catheterization.