Gated myocardial perfusion SPECT underestimates left ventricular volumes and shows high variability compared to cardiac magnetic resonance imaging -- a comparison of four different commercial automated software packages

Abstract

Background: We sought to compare quantification of left ventricular volumes and ejection fraction by different gated myocardial perfusion SPECT (MPS) programs with each other and to magnetic resonance (MR) imaging.

Methods: N = 100 patients with known or suspected coronary artery disease were examined at rest with 99 mTc-tetrofosmin gated MPS and cardiac MR imaging. Left ventricular end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF) were obtained by analysing gated MPS data with four different programs: Quantitative Gated SPECT (QGS), GE MyoMetrix, Emory Cardiac Toolbox (ECTb) and Exini heart.

Results: All programs showed a mean bias compared to MR imaging of approximately -30% for EDV (-22 to -34%, p < 0.001 for all), ESV (-12 to -37%, p < 0.001 for ECTb, p < 0.05 for Exini, p = ns for QGS and MyoMetrix) and SV (-21 to -41%, p < 0.001 for all). Mean bias +/- 2 SD for EF (% of EF) was -9 +/- 27% (p < 0.01), 6 +/- 29% (p = ns), 15 +/- 27% (p < 0.001) and 0 +/- 28% (p = ns) for QGS, ECTb, MyoMetrix, and Exini, respectively.

Conclusions: Gated MPS, systematically underestimates left ventricular volumes by approximately 30% and shows a high variability, especially for ESV. For EF, accuracy was better, with a mean bias between -15 and 6% of EF. It may be of value to take this into consideration when determining absolute values of LV volumes and EF in a clinical setting.

Figure 1

Patient characteristics. Prevalence of different perfusion defect sizes (left) and affected coronary artery territories (right) in the study population. LAD = Left Anterior Descending Artery, RCA = Right Coronary Artery, LCx = Left Circumflex Artery.

Figure 2

Example of delineation. Delineation of the left ventricle in end diastole (ED) and end systole (ES) from MR imaging and MPS using Quantitative Gated SPECT (QGS), MyoMetrix (Myo), Emory Cardiac Toolbox (ECTb) and Exini heart. Images are shown in the short axis (SA), vertical long axis (VLA) and horizontal long axis (HLA). The long axis delineations are shown for illustration purposes. The MPS images were reconstructed iteratively. Quantification of MR images was only performed in contiguous short-axis slice covering the entire ventricle. Long-axis MR images are shown for illustrative purposes. All images are from the same patient.

Figure 3

The absolute difference between MPS and MR imaging for EDV, ESV, SV and LVEF compared to MR imaging and the corresponding MPS program, respectively, for QGS, MyoMetrix, ECTb and Exini, respectively. Note that for most of the measures and programs used, there is a systematic trend in the difference between MPS and MR imaging over the range of values when MR imaging is on the horizontal axis, but this is not apparent when MPS is on the horizontal axis. This implies that there are systematic differences between MR imaging and MPS, and these can not be adjusted for when one only has LV volume values from MPS

Figure 4

Correlation between EDV, ESV, SV and LVEF measured by QGS, ECTb, MyoMetrix and Exini versus MR imaging. Dashed line indicates line of identity, and the solid line, linear regression. SEE denotes the standard error of the estimate

Figure 5

Summary of the percent mean bias ± 2 SD for EDV, ESV, SV and LVEF using the four different MPS quantification programs compared to MR imaging. See text for details on statistical significance of differences between programs