Nierenarterienstenose: Möglichkeiten der Kernspintomographie

Abstract

Non-invasive detection of stenotic lesions of the renal arteries remains an important clinical problem. Recent advances in magnetic resonance angiography represent a significant progress towards achieving non-invasive diagnosis of vascular diseases. The purpose of this study was to evaluate the possibilities of assessment of renal artery stenosis with commonly available hard-and software equipment. Imaging of renal arteries was performed with a ECG-gated fast multiphase gradient echo sequence which allows production of a series of images in different heart phases. Examinations were performed in 15 healthy volunteers and in 12 patients with angiographically verified renal artery stenosis. In 10 patients additional dynamic studies with fast imaging during short breath-holding periods after administration of gadolinium-DTPA served for the assessment of renal perfusion. A superconducting system operating at 1.5 T was used to produce gradient echo sequences with small flip angles and dephasing gradients of constant amplitude. To find the optimal imaging method for depiction of the renal arteries the following parameters were systematically varied: respiratory gating, resolution, number of excitations, slice thickness, phase encoding direction, rephasing gradients, Flip angle and echo time. A good visualization of the vessels was always possible and using the best parameter combination even the narrowed lumen could be assessed in some cases. With this technique or with gadolinium-enhanced dynamic studies the perfusion of the kidneys can be demonstrated. However, quantitation of the stenosis or quantitation of renal perfusion was not possible; even the depiction of the stenotic lesion was successful only in half of the cases. Thus commonly used MR equipment is not yet able to replace more invasive methods in the diagnosis of renal artery stenosis. In order to make MR angiography a successful technique for the assessment of vascular diseases more sophisticated methods that allow a quantitation of flow or velocity across the vessel, will have to be developed.