Noninvasive postoperative angiography for internal mammary artery grafts.

Recently, noninvasive imaging modalities such as electron-beam computed tomography, magnetic resonance angiography, and single-slice helical computed tomography (CT) have emerged as ways to visualize the coronary arteries. With regard to internal mammary artery grafts, however, conventional 3D imaging techniques have failed to demonstrate consistently satisfactory performance. We overcame these limitations by using a novel, multislice, helical CT scanner with 4 detector rows (Aquilion, Toshiba Medical Company). For 3D reconstruction and visualization of the coronary arteries, the volumerendering technique was used. Our first case was of a 71-year-old woman who had undergone 3-vessel coronary artery bypass graft surgery in 1999. At the time of her bypass operation, the left internal mammary artery (LIMA) was used to graft the first diagonal branch of the left anterior descending coronary artery (LAD). Separate saphenous vein grafts were placed at the LAD and the left circumflex coronary artery. The day before the scheduled catheterization procedure, a trial was undertaken to detect the coronary artery bypass grafts and to image the coronary arteries noninvasively with CT. Three-dimensional images were processed using an independent workstation system (Zio M900, AMIN). Figure 1 shows the volume-rendered images that were generated from a 3D image data set with 1.25-mm sections and 0.5-mm phase increments. End-diastolic images free of motion artifacts were reconstructed by absolute-reverse ECG gating. The LIMA bypass graft was clearly identified. A free saphenous vein graft placed at the left circumflex coronary artery was totally occluded at the proximal anastomosis. Another saphenous vein graft placed at the LAD was clearly detected by intravenous enhanced CT angiography. The patency of these grafts was confirmed by conventional coronary angiography (Figure 2). Three-dimensional reconstruction using the volume-rendering technique demonstrated good image quality, permitting the morphology and patency of the graft to be evaluated.