Optimizing accuracy and precision with motion correction of PET myocardial blood flow measurements
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The well-validated diagnostic and prognostic value of quantitative estimates of myocardial blood flow (MBF) and flow reserve (MFR) derived from positron emission tomography1, 2, 3, 4, 5 have generated much enthusiasm for clinical implementation. Quantification of MBF at peak hyperemic stress and MFR can refine referrals for invasive angiography and may potentially improve selection of patients for revascularization.6,7 However, in order to apply these population data in a reliable manner to the management of individual patients, optimization of precision and accuracy is required.8 Patient motion effects are a major driver of both imprecision and inaccuracy. Work by Otaki et al in the present issue of the Journal of Nuclear Cardiology aims to address this issue.9
Recapitulatory table of dynamic motion studies in the literature
Accuracy and Precision
Prior studies have clearly shown the necessity for motion correction to obtain accurate MBF and MFR estimates. However, manual strategies may result in decreased precision as user input generally introduces variability. Otaki et al, in their present study, show that with manual motion correction performed by well-trained operators the test-retest coefficient of variation (CV) for MBF decreases from 16% to 9%. This repeatability study shows that the potential added variability of manual motion correction is offset by the improvement in accuracy which results in matching test-retest MBF estimates. Importantly, they report a low inter-user variability CV of 5% on motion-corrected studies. The excellent results suggest that it is possible to obtain highly repeatable motion correction results within and between operators. The study does however have limitations, as only rest datasets were analyzed whereas the literature has shown that motion is more prevalent and severe during stress.11,13
What is unknown is whether this level of consistency can be routinely achieved at less experienced, high-volume sites. Inconsistent manual motion correction would not only decrease reproducibility, but could reduce accuracy of estimates, particularly in scans without severe motion. Further real-world studies involving multiple sites would be required to understand the magnitude of this potential challenge. Regardless, it appears certain that skill and training in manual motion correction are additional critical challenges for clinical generalization of quantitative cardiac PET MPI.
Challenge and Solution
Regardless of the approach used, the evidence in favor of motion correction is substantial and should now be standard practice for all dynamic PET MPI studies. We applaud Otaki et al for their important contribution and encourage the field to continue work in this area.
A. Poitrasson-Rivière is an employee of INVIA Medical Imaging Solutions. V.L. Murthy has received research funding from Siemens Medical Imaging and research support from INVIA Medical Imaging Solutions. He has served as an advisor to and owns stock options in Ionetix. He has received payment for expert witness testimony on behalf of Jubilant Draximage. He has served as an advisor to Curium and owns stock in General Electric and Cardinal Health. His research is supported by grants from the National Heart, Lung, and Blood Institute (R01HL136685) and National Institute on Aging (R01AG059729).
- 6.Patel KK, Spertus JA, Chan PS, et al. Myocardial blood flow reserve assessed by positron emission tomography myocardial perfusion imaging identifies patients with a survival benefit from early revascularization. Eur Heart J 2019. https://doi.org/10.1093/eurheartj/ehz389.CrossRefPubMedPubMedCentralGoogle Scholar
- 7.Gould KL, Johnson NP, Roby AE, et al. Regional, artery-specific thresholds of quantitative myocardial perfusion by PET associated with reduced myocardial infarction and death after revascularization in stable coronary artery disease. J Nucl Med 2019;60:410-7. https://doi.org/10.2967/jnumed.118.211953.CrossRefPubMedPubMedCentralGoogle Scholar
- 15.Armstrong IS, Memmott MJ, Saint KJ, et al. Assessment of motion correction in dynamic rubidium-82 cardiac PET with and without frame-by-frame adjustment of attenuation maps for calculation of myocardial blood flow. J Nucl Cardiol 2019. https://doi.org/10.1007/s12350-019-01834-5.CrossRefPubMedGoogle Scholar