A VARIABLE THRESHOLD EDGE-DETECTOR FOR IMPROVED QUANTITATION OF GATEDTOMOGRAPHIC IMAGING OF THE LEFT-VENTRICULAR BLOOD-POOL

The accurate measurement of left ventricular volume from tomographic M UGA studies is difficult due to the limited resolving power of the gam ma camera, which causes errors in the detection of the correct ventric ular boundaries. Therefore, the use of fixed threshold or second-deriv ative edge-detectors results in overestimates at small volumes. A vari able threshold edge-detection technique was developed to overcome this . Computer-simulated short-axis slices through the heart over a range of left ventricular dimensions were convolved by the Point Spread Resp onse Function of the system to model the acquired image. The maximum p ixel value and the threshold value required to detect the hue ventricu lar edge from each simulation were then combined into a look-up table for the calculation of the required threshold value. As the dimension of the ventricle decreased, the threshold value chosen to detect the v entricular edge increased. Left ventricular volumes and ejection fract ion measurements were calculated for seven patients using cine-MRI as the gold-standard technique for validation of the proposed method. The single photon emission tomographic studies were analysed using both t he standard second-derivative edge-detection software and the proposed variable threshold technique. The variable threshold technique was sh own to increase significantly the accuracy of ventricular volume measu rements and ejection fraction calculations. The average error in the m easurement of volumes was reduced from 41.4 +/- 45.1% to 18.5 +/- 14.6 % and the accuracy of ejection fraction measurement was increased from 29.7 +/- 4.6% to 11.3 +/- 6.9%.