INTERET DE LA CORRECTION PAR LES GAINS A LA RECEPTION DANS LA DETERMINATION DE LA SURFACE MITRALE EN ECHOCARDIOGRAPHIE BIDIMENSIONNELLE

Distorsion due to inappropriate gain settings interferes significantly with the measurement of mitral valve area by 2D echocardiography. The problem is general and applies to all makes of echocardiographs whether they are mechanical or phased array scanners. The measured mitral surface area may even be false if the level of the recording gain is disregarded. We established a graph of the global distorsion of a system comprising an Aloka SSD 800 phased array sector scanner and a Tektronics hard copy recorder using a 'tissue-equivalent' model and only varying the level of gain. Using these results a computerised program for automatic correction of the mitral surface area, with respect to the gain level used, was developed. The program was validated on a series of 56 patients with mitral stenosis by comparison with the catheter results obtained with the Gorlin formula, peroperative and pathological findings on resected valves. With this echo system in the zone of gain settings studied there was a significant underestimation of the uncorrected surface area. After correction, the distinction between severe and moderate stenosis was better and an improved correlation with the anatomical surface area was obtained. It would therefore appear necessary to calibrate the system used taking both the echocardiograph and the recorder into account. Despite certain limitations, we believe that distorsion curves could be established using 'tissuse-equivalent' models.