effect of reduced photon count levels and choice of normal data on semi-automated image assessment in cardiac spect

The smartzoom multifocal collimator from siemens healthcare was developed to improve the γ-photon sensitivity in myocardial perfusion imaging without truncating the field of view. as part of the iq-spect package, it be used to reduce radiopharmaceutical dose to patients, as well as acquisition time. the aim of this study was twofold: (1) to evaluate the influence of dose reduction in semi-automated mpi scoring, with focus on different strategies for the choice of normal data (count-matched, full-count), and (2) to evaluate the effect of dose reduction afforded by siemens’ iq-spect package. 50 patients underwent tc-99m-sestamibi one-day stress/rest spect/ct. multiple levels of count reduction were generated using binomial thinning. using corridor 4dm, summed stress score (sss) was calculated using either count-matched or full-count normal data. studies were classified as low-risk (sss < 4) or intermediate/high-risk (sss ≥ 4). count reduction using count-matched normal data increases false-normal rate and decreases sensitivity. with full-count normal data, count reduction increases false-hypoperfusion rate, leading to decreased specificity. altogether, rate of reclassification was significant at roughly 67% dose and below. significant bias results from count level of normal data relative to actual patient data. compared to standard lehr, iq-spect should allow for significant dose reduction.