QUANTITATIVE ASSESSMENT OF LEFT-VENTRICUL AR MYOCARDIAL PERFUSION WITH EBCT

Myocardial perfusion is one of the most important functional parameter s of the heart. Presently various indirect methods are used to determi ne coronary blood flow or myocardial perfusion as inertgas-, thermodil ution-, Doppler catheter- and radiopharmacological techniques. Electro n-beam-computed-tomographical technology is able to perform CT data ac quisition with a very short exposure time of 50 ms. Using this method it is not only possible to determine left ventricular volumes but also to measure myocardial perfusion in ml/100 g/min. The measurement of t he left myocardial perfusion is performed using the short axis view. T his position is obtained by moving the table 25 degrees to the patient 's right and 15 degrees caudally. To determine the position of the lef t ventricle, a localization scan is obtained in multi-slice-mode using all for target-rings, thus obtaining 8 tomographic levels over 68 mm (each tomographic level having a slice thickness of 7 mm, with an inte rslice gap of 4 mm between each two adjacent tomographic levels). In t his short axis position, using the multi slice flow mode with 3 target -rings and after administration of 50 mi of contrast medium intravenou sly with a flow of 3 ml/s, 6 tomographic levels are imaged. Each tomog raphic level is obtained 13 times at 80% of the R-R-interval at each 2 or 3 heart beat (EGG-gated). The left ventricular myocardial contrast enhancement is measured by drawing manually the outline of the left v entricular myocardium using time-density-software of the Imatron works tation. For calculation of the myocardial perfusion the socalled ''slo pe method'' is used and the results are expressed as the maximum slope of enhancement of the myocardium divided by the difference of the pre contrast and peak CT-value in the left ventricle. The global myocardia l perfusion is calculated as a mean of all evaluated tomographic level s. In this study left ventricular volumes as enddiastolic volume endsy stolic volume and stroke volume were measured and ejection fraction an d cardiac output calculated. The measurements were performed in the lo ng axis view This view is obtained by moving the table 15 degrees to t he patients left in a horizontal position. In this long axis position 6 tomographic levels are imaged using the multi-slice-cine mode with 3 target-rings after administration of 50 mi of contrast medium intrave nously with a flow of 3 ml/s. Each tomographic level is obtained 13 ti mes starting at 0% of the R-R-interval (EGG-triggering). The exposure time is 50 ms with an interscan time delay of 8 ms. In 9 studied patie nts of whom one had 3 significant coronary artery stenotic lesions (>5 0%), 2 patients had each 2 non significant stenotic lesions (<50%) and 6 revealed nearly normal coronary angiograms. The mean global myocard ial perfusion was 70 ml/100 g/min (min. 32 and max. 116 ml/100 g/min). This mean value of 70 ml/100 g/min is reflecting 5% of the cardiac ou tput supposing that the mean heart weight of these patients was 300 g. In this study the mean of the left ventricular muscle mass determined by the use of EBCT was 130 g. A comparative evaluation of coronary an giographic findings in these patients with the measured myocardial per fusion values revealed, that it is not sufficient to look only at the absolute values of the measured myocardial perfusion. Furthermore it s eems to be necessary to interprete these perfusion values with respect to the calculated cardiac output. Additional studies of well defined patients groups are necessary to determine normal values of myocardial perfusion at rest in patients with and without coronary artery diseas e. This seems to be important as comparative analysis of myocardial sc intigraphic and EBCT-studies is difficult because of methodical inhere nt differences. The results of this study suggest that despite the pre sence of some beam hardening artifacts it is possible to measure myoca rdial perfusion using EBCT in patients with suspected coronary artery disease in the daily clinic workup. For the interpretation of these my ocardial perfusion values it is necessary to pay special attention to heart rate and especially to the calculated cardiac output.