Calculation of the left ventricular ejection fraction without edge detection: application to small hearts

Quantitative gated SPECT (QGS) software has been reported to overestimate the left ventricular ejection fraction (LVEF) in patients with small hearts. This finding is caused by the inaccurate detection of the endocardial surface of the left ventricle (LV) due to low resolution and partial-volume effects. In this article we develop a method to calculate the LVEF from gated SPECT data without edge detection and compare it with the QGS method of calculating the LVEF.

The short-axis images were transformed to the prolate spheroid coordinate system, and detection of the layer of maximum counts (a surface area of maximum counts) was made. First, the volume enclosed by the layer of maximum counts (V(max)) was calculated; then the corresponding ejection fraction [(LVEF)(max)] was calculated. The LVEF was calculated by multiplying the (LVEF)(max) by a constant factor, which was determined from a series of calculations made using QGS on larger hearts. In computer simulations the end-diastolic left ventricular volume (EDV) and the targeted LVEF (tLVEF) were varied to produce LVs of different sizes. The LVs were modeled by 2 confocal hemiellipsoids with 7 different EDVs. The tLVEF was increased from 25% to 75%, in 5% step-size increments, for a total of 11 different ejection fractions. These datasets were then smoothed, creating a total of 77 smoothed sets. The smoothed images were processed by the QGS method and by our method. In patient studies, 58 patient datasets were processed by the QGS method and by our method. No attenuation correction was performed on these datasets. The patients were divided into 2 groups: 44 patients with large hearts (EDV > or = 80 mL) and 14 patients with small hearts (EDV < 80 mL).

In computer simulations, the QGS method and our method performed well when imaging large EDVs (EDV > or = 80 mL). Our method derived better results than did the QGS method for small EDVs. In patient studies the LVEF calculated by our method matched well with the QGS LVEF in the 44 patients with large hearts. The correlation coefficient between them was found to be 0.957. Of the 14 patients with small hearts, the LVEFs of 5 patients were severely overestimated by the QGS method compared with the results obtained with our method.

It is possible to calculate the LVEF without edge detection. Compared with QGS LVEF, our method gave better results for small LVs in computer simulations.