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 may 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.
Key WordsMPI SPECT/CT Tc-99m MIBI dose reduction normal data
Myocardial perfusion imaging
Total perfusion deficit
Summed stress score
Summed rest score
Counts per pixel
The present work was performed in (partial) fulfillment of the requirements for obtaining the degree “Dr. med.”
Matthias Wetzl has nothing to declare. James C. Sanders has been supported in the past by a collaboration agreement with Siemens Molecular Imaging that is not directly related to this project. Torsten Kuwert has received honoraria for lectures on behalf of Siemens Molecular Imaging. Torsten Kuwert and Philipp Ritt: the Clinic of Nuclear Medicine in Erlangen has a research cooperation with Siemens on the field of SPECT/CT, but not related to the data contained in this manuscript.
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