Gated Myocardial Perfusion SPECT: Algorithm-Specific Influence of Reorientation on Calculation of Left Ventricular Volumes and Ejection Fraction

Gated myocardial perfusion SPECT allows calculation of end-diastolic and end-systolic volumes (EDV and ESV, respectively) and left ventricular ejection fraction (LVEF). The quantification algorithms QGS (quantitative gated SPECT), 4D-MSPECT, and CARE heart show a good correlation with cardiac MRI. Nevertheless, differences in contour finding suggest algorithm-specific effects if heart axes vary. The effect of tilting heart axes on gated SPECT was quantified as a possible source of error. Methods: Sixty men underwent gated SPECT (450 MBq of Tc-99m-tetrofosmin or sestamibi, 8 gates/cycle). After correct reorientation (R-0), datasets were tilted by 5, 10, 15, 20, 30, and 45 along both long axes (R-5, R-10, R-15, R-20, R-30, and R-45, respectively). EDV, ESV, and LVEF were calculated using QGS, 4D-MSPECT, and CARE heart. Because a 15 tilt could be a maximum possible misreorientation in routine, R-0 and R-15 results were analyzed in detail. Absolute-difference values between results of tilted and correctly reoriented datasets were calculated for all tilts and algorithms. Results: QGS and CARE heart succeeded for R-0 and R-15 in all cases, whereas 4D-MSPECT failed to find the basal plane in 1 case (patient B). R-2 values between paired R-15/R-0 results were 0.992 (QGS), 0.796 (4D-MSPECT; R-2 = 0.919 inn = 59 after exclusion of the failed case), and 0.916 (CARE heart) for EDV; 0.994 (QGS), 0.852 (4D-MSPECT; R-2 = 0.906 in n = 59), and 0.899 (CARE heart) for ESV; and 0.988 (QGS), 0.814 (4D-MSPECT; R-2 = 0.810 in n = 59), and 0.746 (CARE heart) for LVEF Concerning all levels of misreorientation, 1 patient was excluded for all algorithms because of multiple problems in contour finding; additionally for 4D-MSPECT patient B was excluded. In the 45 group, QGS succeeded in 58 of 59 cases, 4D-MSPECT in 58 of 58, and CARE heart in 33 of 59. Mean absolute differences for EDV ranged from 5.1 +/- 4.1 to 12.8 +/- 10.5 mL for QGS, from 6.7 +/- 6.3 to 34.2 +/- 20.7 mL for 4D-MSPECT, and from 5.4 +/- 5.6 to 25.2 +/- 16.1 mL for CARE heart (tilts between 5 and 45). Mean absolute differences for ESV ranged from 4.1 +/- 3.7 to 8.0 +/- 9.4 mL for QGS, from 5.6 +/- 8.0 to 10.0 +/- 10.5 mL for 4D-MSPECT, and from 5.4 +/- 5.6 to 25.5 +/- 16.1 mLfor CARE heart. Mean absolute differences for LVEF ranged from 1.1% +/- 1.0% to 2.2% +/- 1.8% for QGS, from 4.0% +/- 3.5% +/- to 8.0% +/- 7.1 for 4D-MSPECT, and from 3.4% +/- 2.9% to 9.2% +/- 6.0% for CARE heart. Conclusion: Despite tilted heart axes, QGS showed stable results even when using tilts up to 45. 4D-MSPECT and CARE heart results varied with reorientation of the heart axis, implying that published validation results apply to correctly reoriented data only.