Measuring the thickness of articular cartilage from MR images.

We have developed an algorithm to estimate and display the spatial distribution of the thickness of articular cartilage in human knees. We used a simulation to derive the most appropriate formula for estimating thickness in digital images. The algorithm was tested by imaging a thickness phantom and comparing the results with the known dimensions of the phantom. The results demonstrated that the maximum error encountered in estimating thickness is one pixel while the average error is 0.4 pixels. We imaged a human knee on a cadaver in two separate sessions and used the two image sets to derive thickness maps of the patellar articular cartilage. The thickness maps generated independently from these image sets were very similar, indicating the reliability of the method in deriving accurate thickness estimates. J. Magn. Reson. Imaging 2001;13:120-126.

Effects of internal mammary artery pedicle coronary artery bypass grafting on aortic valve leaflet positioning.

Approximately 50% of all patients who require replacement of the aortic valve (AVR) also require coronary artery bypass grafting (CABG) for concomitant coronary artery disease. Internal mammary artery (IMA) pedicle grafts are being used with increasing frequency for this purpose. Since the ostia of the IMA are considerably downstream from the sinus of Valsalva we hypothesized the CABG would change the local coronary flow dynamics and possibly alter the timing of both natural and prosthetic valve opening and closing dynamics. Both IMA'S were dissected as pedicle grafts in five pigs and the animals were put on cardiopulmonary bypass. Anastomotic sites were the proximal 1/3 of the left anterior descending and proximal 1/5 of the right coronary arteries. Aortic root, left ventricular and right ventricular pressures were measured and flowmeter transducers were placed on the aortic root, the left main coronary artery, the right coronary artery, the left IMA and the right IMA for measuring flows. Echocardiographic images of the aortic valve, in the longitudinal view, were recorded with a simultaneous ECG. Time points were defined during each cardiac cycle based upon characteristic points in the native coronary hemodynamics. These were identified at 8, 14 and 22% of the cycle (valve opening) and 38, 45 and 55% of the cycle (valve closing). Calculations were made based upon each cycle being initiated with the ECG R wave peak. Significant alterations in flow patterns were identified and quantitated between native coronary and IMA grafts. Only minor changes in valve positioning were identified. These differences in natural valve leaflet position occurred at 22% and 45% of the cycle.