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Vascular Surgery - part 2

Gradient phân đoạn trình tự, phân đoạn turbo-FLASH, 3-D TOP, mua lại xoắn ốc, và echo phẳng hình ảnh (13,24-26). MRA trực quan của mạch vành gần tương quan tốt (95%) với các mạch máu thông thường (13,27). Hình ảnh của mạch vành gần hơn nhiều so với hình ảnh tàu xa và stenoses nghiêm trọng được xác định chính xác hơn (27) | 106 Parti Imaging Techniques ventional spin echo segmented gradient-echo sequences segmented turbo-FLASH 3-D TOF spiral acquisitions and echo planar imaging 13 24-26 . MRA visualization of proximal coronary vessels correlates well 95 with that of conventional angiography 13 27 . Visualization of proximal coronary vessels is far superior to distal vessel imaging and severe stenoses are more accurately identified 27 . MR imaging can detect a high proportion of severe stenoses but only a low proportion of moderate stenoses. The sensitivity and specificity of coronary MRA for detecting severe stenosis are 85 and 80 respectively. A moderate decrease in blood flow results in a significant decrease of sensitivity to 38 26 . The advantages of coronary arterial imaging with MR have been mostly noted in the visualization of anomalous coronary vessels 28 . Although conventional angiography can show anomalous vessels the position of the vessel relative to the aorta and adjacent organs can be difficult to appreciate. MRA can clearly demonstrate the passage of the anomalous vessels anterior or posterior to the aorta and their spatial relationship to nerves venous and other parenchymal structures making it a useful preoperative imaging tool 28 29 . Overall coronary MRA for identification of coronary stenoses is not generally accepted with the currently existing technology. Further refinement of imaging techniques is necessary before coronary MRA will achieve widespread acceptance. Aortic Arch and Thoracic and Abdominal Aorta MRA can delineate the aortic arch and its branches with a high degree of resolution Fig. 7.4 . Aortic dissections can be reliably diagnosed and classified as either type A involving the ascending aorta or type B distal to the left subclavian artery by MRA. MRA accurately demonstrates the relationship of branch arteries to true and false lumen anatomy as well as defining the proximal and distal extents of the dissection flap Fig. 7.5 . Non-nephrotoxic contrast