Left ventricular volume calculation by first-pass radionuclide angiography

A new radionuclide technique for calculation of left ventricular (LV) volume by the first-pass (FP) method was developed and evaluated. Using the method proposed by Nichols et al., LV volume can be measured using the following equation: Cv = Cm/(L/d). V = (Ct/Cv) x d3 = (Ct/Cm) x L x d3, where V = LV volume, Cv = voxel counts, Cm = the maximum LV count, Ct = the total LV count, L = LV depth where the maximum count is obtained, and d = pixel size. The first phantom study was performed by flushing Tc-99m into a cylindrical container using a system through which water ran at 5 L/min. The container using a system through true volume and volume measured by this method were very highly correlated (r = 0.99, p<0.001, n = 15). A second phantom study was done to determine the minimum LV peak count during LV volume calculation by this method. A 154 ml container was imaged 63 times while varying the imaging time. It was shown that the peak counts obtained by routine FP studies sufficient to calculate LV volume. Next, this theorem was applied to the FP end-diastolic (ED) LV image obtained in the 30 deg right anterior oblique position in 26 patients. The LV ED maximum count and total count were obtained. Maximum LV depth was taken to be the maximum width of the LV on the FP ED image, on the asssumption that ventricle has a circular cross-section. Using the above equation, the LV ED volume (EDV) was also calculated by the area-length method. Then, the FP EDV was compared to be the contrast EDV. These two values showed a strong positive correlation (r = 0.95, p<0.001, n = 26). In conclusion, this new method of calculating LV volume is considered to be especially useful in evaluating cardiac function with Tc-99m-labeled cardiac blood flow imaging agents. (author)