The long way to dose reduction in myocardial perfusion imaging

Abstract

In the last decade, the concerns about radiation in myocardial perfusion imaging (MPI) have propelled the development of high-efficiency cardiac SPECT scanners, innovative collimators and iterative reconstruction algorithms with resolution recovery (IRR) for performing low-dose myocardial perfusion studies.1 However, the extent to which, using this new technology, the patient dose can be reduced is still unknown today.Several studies have shown that, using the IRR algorithms, it is possible to reduce the patient dose by half and at the same time, to provide diagnostic results equivalent to conventional reconstruction algorithms, such as ordered subset expectation maximization (OSEM) and filtered back projection (FBP).2-6 The recommended activities, per single scan, according to the American Society of Nuclear Cardiology (ASNC), may now range from 148 MBq (stress-only protocol, new technology, body mass index (BMI) = 25 kg/ m 2 ) to 1332 MBq (second injection in a one-day stress/rest protocol, GP gamma camera, BMI = 35 kg/m 2 ), resulting in effective doses of between 1.0 and 10.5 mSv.7 However, the IRR algorithms have demonstrated the potential to reduce the patient dose below 50% of the reference in an anthropomorphic phantom study 8 and in two clinical studies, 9,10 mostly in the presence of normal-weight patients (between 18.5 and 24.9 kg/m 2 of BMI). The study of Juan Ramon et al. 11 in this issue of the Journal of Nuclear Cardiology is the first study that investigates the extent to which patient dose can be reduced in cardiac SPECT through the optimization of reconstruction process. The authors simulated different dose levels (from 100 to 12.5% of the standard dose) using cardiac SPECT data modified to contain realistic simulated perfusion defects. The first step of this study is to find the best set-up of the reconstruction parameters for each reconstruction method and for each dose level considered in the study without the comparison with the conventional clinical outcome. The reconstruction methods considered were (1) FBP, (2) OSEM with attenuation, scatter, and resolution corrections and (3) OSEM with scatter and resolution corrections only. For each of these reconstruction strategies and dose level, the authors conducted a receiver operating characteristics (ROC) study based on the total perfusion deficit (TPD) score computed by the Quantitative Perfusion SPECT (QPS) software package. TPD score quantifies the non-uniformity of myocardial perfusion in the left-ventricle polar maps with respect to normal limits derived from a series of reference databases created from normal MPI scans. The authors generated separate reference databases depending on reconstruction strategy (reconstruction method, number of iteration and/ or filter parameter) and dose level, optimizing in this way also the automatic quantification process to each specific polar map. The results of the study suggest that, by using OSEM with all the corrections, a reduction of dose level to 25% could be achieved without limiting diagnosti...

Personalized Models for Injected Activity Levels in SPECT Myocardial Perfusion Imaging

“…Although these studies have demonstrated the potential for dose reduction in SPECT-MPI, the majority of them, if not all, have been focused on reducing the administered activity level uniformly across patients. However, the level of required dose may differ from patient to patient in order to achieve a consistent diagnostic accuracy across patients [26][27][28][29]. Some studies have shown that the amount of dose reduction should be different for obese and normal-weight patients [26], and that injected dose should depend on patient weight or body mass index (BMI) so that the acquired count statistics is maintained [30][31][32].…”