Variability of left ventricular ejection fraction and volumes with quantitative gated SPECT: influence of algorithm, pixel size and reconstruction parameters in small and normal-sized hearts

Several software packages are commercially available for quantification of left ventricular ejection fraction (LVEF) and volumes from myocardial gated single-photon emission computed tomography (SPECT), all of which display a high reproducibility. However, their accuracy has been questioned in patients with a small heart. This study aimed to evaluate the performances of different software and the influence of modifications in acquisition or reconstruction parameters on LVEF and volume measurements, depending on the heart size. In 31 patients referred for gated SPECT, 642 and 1282 matrix acquisitions were consecutively obtained. After reconstruction by filtered back-projection (Butterworth, 0.4, 0.5 or 0.6 cycles/cm cut-off, order 6), LVEF and volumes were computed with different software [three versions of Quantitative Gated SPECT (QGS), the Emory Cardiac Toolbox (ECT) and the Stanford University (SU-Segami) Medical School algorithm] and processing workstations. Depending upon their end-systolic volume (ESV), patients were classified into two groups: group I (ESV>30 ml, n=14) and group II (ESV<30 ml, n=17). Agreement between the different software packages and the influence of matrix size and sharpness of the filter on LVEF and volumes were evaluated in both groups. In group I, the correlation coefficients between the different methods ranged from 0.82 to 0.94 except for SU-Segami (r=0.77), and were slightly lower for volumes than for LVEF. Mean differences between the methods were not significant, except for ECT, with which LVEF values were systematically higher by more than 10%. Changes in matrix size had no significant influence on LVEF or volumes. On the other hand, a sharper filter was associated with significantly larger volume values though this did not usually result in significant changes in LVEF. In group II, many patients had an LVEF in the higher range. The correlation coefficients between the different methods ranged between 0.80 and 0.96 except for SU-Segami (r=0.49), and were slightly worse for volumes than for LVEF values. In contrast to group I, however, inter-method variability was quite large and most mean LVEF differences were significant. LVEF was systematically highest with ECT and lowest with SU-Segami. With QGS, changes in matrix size from 642 to 1282 were associated with significantly larger volumes as well as lower LVEF values. Increasing the filter cut-off frequency had the same effect. With SU-Segami, a larger matrix was associated with larger end-diastolic volumes and smaller ESVs, resulting in a highly significant increase in LVEF. Increasing the filter sharpness, on the other hand, had no influence on LVEF though the measured volumes were significantly larger. (orig.)