Background: A novel ultra-fast solid-state cardiac camera (Discovery NM 530c, General Electric) allows much shorter acquisition times compared to standard dual-detector SPECT cameras. This design enables investigation of the potential for early myocardial perfusion imaging (MPI) following a rest injection of technetium-99m (Tc-99m) rather than the conventional 45-60 minute delay in image acquisition.
Methods: A total of 30 patients underwent MPI at rest using Tc-99m sestamibi (n = 9) or tetrofosmin (n = 21). A 12 minute image acquisition in list mode was performed immediately following isotope injection. Patients also underwent a conventional delayed image acquisition 60 minutes following the rest isotope injection (image acquisition over 4 minutes). The immediate 12 minute acquisition was divided into three 4-minute intervals for image reconstruction (0-4, 4-8, and 8-12 minutes). The perfusion images were interpreted by two experienced physicians who evaluated each study for overall image quality (good, acceptable, or unacceptable) and graded each image using the summed rest score (SRS) and the standard 17-segment, 5-point scale model.
Results: The images acquired in the 0-8 minute time interval were predominantly uninterpretable due to excessive blood pool uptake. The images acquired in the 8-12 minute time interval were interpretable and compared to the conventional images obtained at 60 minutes. Overall image quality was better on the 60 minute image (17 good, 13 acceptable) compared with 8-12 minute image (3 good, 25 acceptable, 2 unacceptable). Sixteen of the 30 patients had an improvement in overall image quality by at least one category using the 60 minute delayed image. Nine of the 30 patients (2 Tc-99m sestamibi; 7 Tc-99m tetrofosmin) had at least one uninterpretable myocardial segment due to liver and/or bowel overlapping the myocardium on the 8-12 minute images vs 1 patient (1 myocardial segment) with this problem on the 60 minute delayed images (P = .005). Uninterpretable segments (total of 16) on the 8-12 minute images were confined to the apex and inferior wall. The mean SRS of the interpretable 8-12 minute images (n = 21) was 3.2 (95% confidence intervals; 1.0, 5.4) compared to 1.6 (95% confidence intervals; 0, 3.3) on the 60 minute delayed images in those patients (P = .005).
Conclusions: Overall image quality was better with fewer uninterpretable studies and a lower SRS on the rest images obtained at 60 minutes compared to early image acquisition (8-12 minutes following isotope injection). These findings do not support the routine use of early image acquisition with this new solid-state ultra-fast camera system.