| Popis: |
Vascular structures in the arterial system are well visualized with magnetic resonance imaging. As rapidly moving blood appears black when imaged with the spin-echo technique because protons in motion move out of the imaging slice after they are excited, a blood vessel can be seen as a black structure [1]. Coronary artery bypass grafts were first seen with magnetic resonance imaging as early as 1983 using the spin-echo technique [2]. When viewed in cross-section they appear as white circles with black lumens. Bypass grafts are generally recognized by their anatomic location in relation to the ascending aorta and the native coronary arteries. Fig. 1 is a schematic of where saphenous vein coronary artery bypass grafts typically are located. The internal mammary arteries are also suitable bypass graft material and the left internal mammary is positioned on the inner aspect of the chest wall. When used as a graft it can be seen in the anterior mediastinum until it inserts into the left anterior descending artery. Therefore all conduits used for coronary bypass can be identified by their anatomic location. In general, though, only patent bypass grafts are recognizable, as grafts without high blood flow will not be distinguished from surrounding tissues. Bypass grafts that are not seen are presumed occluded, although it is possible that if flow through a bypass graft were very low, either because of disease in the bypass graft or in the coronary artery it supplies, it might not be visualized. |
