Clinical Utility of Enhanced Relative Activity Recovery on Systolic Myocardial Perfusion SPECT – Lessons from PET.

Abstract

SPECT and PET myocardial perfusion images (MPI) show greater myocardial intensity and homogeneity in systole than diastole due to greater systolic myocardial thickness, less partial volume loss and enhanced activity recovery. Consequently, conventional MPI obtained from whole cardiac cycles have lower myocardial intensity and greater heterogeneity than systolic images. Considering relative activity distribution on SPECT systolic images may add clinical utility to whole cycle images and wall motion. Methods: Patients undergoing coronary angiogram within 4 months after SPECT MPI were reviewed. Images were interpreted by 2 blinded readers using 17-segment, 5-point scale to determine summed rest, stress & difference score on conventional and systolic images (SRS, SSS & SDS) in 603 patients (55.6% No-CAD and 44.4% CAD). Studies were considered normal when SSS < 4 and SDS < 2. Results: In No-CAD group, systolic SSS was lower than SSS from conventional images (2 ± 2.3 vs. 3 ± 2.6; P < 0.001). In contrast, SSS derived from systolic and conventional images were not different in obstructive CAD group (9.1 ± 7.6 vs. 9.2 ± 7.4; P = 0.559). Considering systolic images increased true negative studies from 27.2% to 43.3% (P < 0.001) while false positive studies decreased from 28.4% to 12.3% (P < 0.001). True positive (38% vs. 37.2%, P = 0.505) and false negative studies (6.5% vs. 7%, P = 0.450) were not significantly changed. Diagnostic accuracy increased from 65.2% to 80.8% (P <0.001). Conclusion: For gated SPECT MPI, considering relative activity distribution on systolic images reduced false positive studies and improved diagnostic accuracy.