Abstract
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Objectives Numerous technical advancements have recently been introduced for cardiac SPECT, such as dedicated solid-state detectors and specialized collimators, which allow for a reduced acquisition time (AT) while maintaining sufficient image quality. The aim of our study was to evaluate the effect on image assessment of AT reduction afforded by cardio-focal collimators.
Methods 50 patients underwent a Tc-99m-sestamibi cardiac one-day stress/rest SPECT/ CT examination according to our national guidelines (1). Gated SPECT/CT was acquired 60 min p.i. of, on average 6.4±0.6 mCi (237 ± 22 MBq) (stress), and 19 ± 0.8 mCi (704 ± 31 MBq) (rest) using a Siemens Symbia T6 equipped with cardio-focal collimators (IQ-SPECT). The time per view was 30 s with 17 stops (=34 views). The full time projection data thus consisted of counts collected over 8.5 min (=17*30s). Multiple levels of count reduction (equivalent to 7.1, 5.6, 4.3, 2.8, and 1.4 min acquisitions) were generated using binomial subsampling of the full time data. Using the Corridor 4DM application, the summed stress, rest and difference scores (SSS, SRS, SDS) were calculated. Studies were classified as low-risk (SSS<4, SDS<3) or intermediate/high-risk (SSS≥4, SDS≥3) for a cardiac event, as recommended in the literature (1,2).
Results With decreasing count levels, the SSS, SRS, and SDS remained relatively stable until ATs of 4.3 min. They increased on average by 6.7, 1.8, and 5.6 points, respectively, when reducing AT from 8.5 to 1.4 min. The rate of reclassification between low-risk and intermediate/high-risk was significant for the SSS and SDS at ATs of 2.8 min and 1.4 min.
Conclusions A decreased AT could potentially lead to false-positives. The rest studies are more robust against AT reduction due to the initially better image statistics. The results indicate that for our protocol the AT could be reduced to 4.3 min (15s per view) without negative effects, which corresponds to ~3 min AT for recommended injected activities in the US (3).