Relative disagreement among different software packages in PET-flow quantitation: An appeal for consistency

Abstract

Positron emission tomography (PET) is increasingly applied to assess myocardial perfusion in conjunction with global and regional myocardial blood flow (MBF) quantitation in mL g min in patients with suspected and/ or known CAD. While the stress-related regional myocardial perfusion defects commonly identify the ‘‘culprit’’ or the most-advanced CAD lesion in multivessel disease, the hemodynamic significance of lesssevere, intermediate CAD lesions with still homogenous radiotracer uptake may be identified by corresponding regional reductions in hyperemic MBF and/or myocardial flow reserve (MFR = MBF-stress/MBF-rest). In this respect, the concurrent assessment of PET-determined MFR has been appreciated to provide not only the additional diagnostic value, but it carries also important prognostic information in patients with subclinical and clinically manifest CAD. The reproducibility of such MBF quantitation with PET has been performed mainly in healthy volunteers with and without cardiovascular risk factors. These data have convincingly demonstrated that PET-determined serial MBFs during pharmacologic-stimulated hyperemia and at rest can be employed reliably and are reproducible for quantitation of effects of preventive medical intervention, gastricbypass-induced weight loss, and/or behavioral interventions related to weight, diet, and physical activity on coronary circulatory dysfunction. Subsequently, the reproducibility of PET-flow studies among different software tools was investigated. For example, Slomka et al. compared MBF values obtained from three software tools such as QPET, syngo MBF, and PMOD in individuals with or without obstructive CAD. And indeed, the global and regional MBF and MFR values did closely correlate between the three software packages (correlation coefficient r for global values ranging from 0.88 to 0.92 and for regional values from 0.78 to 0.94, respectively), which was reflected by similar mean MFR values (QPET: 3.39 ± 1.22, Syngo MBF: 3.41 ± 0.76, and PMOD: 3.66 ± 1.19, respectively). In this issue of the Journal of Nuclear Cardiology, Monroy-Gonzalez et al. report that in patients with normal stress-rest PET perfusion images, two out of three comparisons were outside the limits of agreement, while in patients with reversible perfusion deficits suggesting ischemia, comparisons of all software packages of global hyperemic MBFs and MFR were outside the limits of established agreement. In addition, there was an agreement of hyperemic MBFs and MFR mostly only for the LAD distribution. Such observations outline that results of MBF quantitation with different software packages are not necessarily interchangeable. Such observations may contradict the results from Slomka et al.’s study which described quite similar MFR values for each vascular territory except for some disagreement in respect of the RCA distribution due to the influence of high spill-over fraction, a problem familiarly known for N-ammonia PET images. PETflow studies with other positron-emitting radiotracers such as Rubidium and O-water also yielded a goodto-excellent agreement between the observations made using different software packages. The reason for these discordant observations may remain uncertain and Reprint requests: Thomas H. Schindler MD, PhD, Division of Nuclear Medicine, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S. Kingshighway, St. Louis, MO, 63110; [email protected] J Nucl Cardiol 2020;27:1234–6. 1071-3581/$34.00 Copyright 2019 American Society of Nuclear Cardiology.