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

Abstract

Gated myocardial perfusion SPECT allows calculation of enddiastolic 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 99m Tc-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 5 0.919 in n 5 59 after exclusion of the failed case), and 0.916 (CARE heart) for EDV; 0.994 (QGS), 0.852 (4D-MSPECT; R 2 5 0.906 in n 5 59), and 0.899 (CARE heart) for ESV; and 0.988 (QGS), 0.814 (4D-MSPECT; R 2 5 0.810 in n 5 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°g roup, 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 6 4.1 to 12.8 6 10.5 mL for QGS, from 6.7 6 6.3 to 34.2 6 20.7 mL for 4D-MSPECT, and from 5.4 6 5.6 to 25.2 6 16.1 mL for CARE heart (tilts between 5°and 45°). Mean absolute differences for ESV ranged from 4.1 6 3.7 to 8.0 6 9.4 mL for QGS, from 5.6 6 8.0 to 10.0 6 10.5 mL for 4D-MSPECT, and from 5.4 6 5.6 to 25.5 6 16.1 mL for CARE heart. Mean absolute differences for LVEF ranged from 1.1% 6 1.0% to 2.2% 6 1.8% for QGS, from 4.0% 6 3.5% to 8.0% 6 7.1% for 4D-MSPECT, and from 3.4% 6 2.9% to 9.2% 6 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.

Reference Ranges for LVEF and LV Volumes from Electrocardiographically Gated 82Rb Cardiac PET/CT Using Commercially Available Software

“…Differences in the algorithms for definition of endocardial and epicardial borders and definition of the base and valve planes are the most likely explanation for this observation. For example, QGS uses a 3-dimensional model of the heart without specific geometric assumptions of horizontal or transversal long axes, ECTb uses a 2-coordinate system (cylindric coordinate for basal and mid-myocardial segments but spheric coordinate for the apex), and 4DM requires the heart base to be perpendicular to the chosen long axes (21). Moreover, ECTb and QGS valve-plane definition models assume that the septal wall is shorter than the lateral wall; consequently, the basal limits are independently estimated on each side of the left ventricle, whereas 4DM assumes that the basal limits are the same in the septal and lateral walls (22,23).…”

Tracking a therapeutic response: How reliable are serial measurements of LV perfusion and function?

“…This concept was tested in a large population (984 patients), whose stress and rest gated SPECT studies underwent the same 15 degrees change in reorientation angles during processing as described above for Knollman’s data (2). The results of paired processing and quantification are shown in Table 2, and demonstrate a very substantial improvement in Δrepro.…”

“…For example, a paper by Knollman et al investigated the variation in quantitative LV function measurements resulting from a simple 15 degrees change in the reorientation angles during processing of 59 gated SPECT datasets. The patient population comprised a good range of LVEFs (20%–80%) end-systolic volumes (ESVs) and end-diastolic volumes (EDVs), which were quantified using three different software algorithms - and while correlation coefficients were generally high, the most reproducible algorithm still produced differences of 2.8%, 7.5ml and 9ml for LVEF, ESV and EDV, respectively, at the 95% confidence interval level (2). In layman’s terms, 5% of the time one should expect quantitative differences greater than those listed above as a consequence of just altering the reorientation angle by 15 degrees during reconstruction.…”

The effect of end-systolic volume on ejection fraction in gated myocardial perfusion scintigraphy

“…For example, increasing zoom factor or changing filter type or changing cut-off value in butter worth filter. However, the use of these applications in routine is not practical and it has been reported that EF values were overestimated in these studies, as well 18 .…”