Quantitative evaluation of left-sided valvular regurgitation by gated single photon emission computed tomography

Severity of aortic and mitral regurgitations was quantitatively evaluated using gated single photon emission computed tomography (SPECT). Data were acquired from 36 views over 360 degrees using dual headed cameras after equilibration of 30 mCi of Tc-99 m red blood cells. Cardiac cycles were divided into 12 frames. Absolute right and left ventricular end-diastolic and end-systolic volumes were calculated based on the number of boxels within a ventricular border determined by isocount method. The optimal threshold level (OT) for delineating ventricular border was determined by the following equation: OT = 0.47 · BG + 44.2 (%), where BG is background level expressed as the ratio (%) of background to maximum ventricular count in the reconstructed image. Then the regurgitant fraction (RF) were calculated by following equation: RF = 1-(1/SVR), where SVR is stroke volume ratio calculated from left ventricular storke volume devided by right ventricular stroke volume. Planar gated blood pool studies were also performed using slant hole collimator and SVR was calculated using stroke volume image. In 20 patients without valvular regurgitation and/or shunt diseases, RF was 2.3 ± 8.6 % (mean ± SD) by SPECT and RF of 20 patients with left-sided valvular diseases was 41.0 ± 15.6 % (p < 0.001). By SPECT, RF of mild regurgitation (1 to 2 degrees of Sellers classification) was 32.8 ± 13.5 % (n = 8) and significantly higher than control group (p < 0.001). RF of 3 degree was significantly higher than mild regurgitant group (49.9 ± 13.5 %, n = 7). When normal upper limit of RF was determined to be the mean + 2 SD of control group, the sensitivity and specificity for the diagnosis of the presence of regurgitation was 95 % and 100 % by SPECT and 75 % and 95 % by planar study. In conclusion our new method for the evaluation of regurgitant fraction of left-sided valvular disease using SPECT was reliable. (author)