Validation of an axially distributed model for quantification of myocardial blood flow using 13N-ammonia PET
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Estimation of myocardial blood flow (MBF) with cardiac PET is often performed with conventional compartmental models. In this study, we developed and evaluated a physiologically and anatomically realistic axially distributed model. Unlike compartmental models, this axially distributed approach models both the temporal and the spatial gradients in uptake and retention along the capillary.
We validated PET-derived flow estimates with microsphere studies in 19 (9 rest, 10 stress) studies in five dogs. The radiotracer, 13N-ammonia, was injected intravenously while microspheres were administered into the left atrium. A regional reduction in hyperemic flow was forced by an external occluder in five of the stress studies. The flow estimates from the axially distributed model were compared with estimates from conventional compartmental models.
The mean difference between microspheres and the axially distributed blood flow estimates in each of the 17 segments was 0.03 mL/g/minute (95% CI [−0.05, 0.11]). The blood flow estimates were highly correlated with each regional microsphere value for the axially distributed model (y = 0.98x + 0.06 mL/g/minute; r = 0.74; P < .001), for the two-compartment (y = 0.64x + 0.34; r = 0.74; P < .001), and for three-compartment model (y = 0.69x + 0.54; r = 0.74; P < .001). The variance of the error of the estimates is higher with the axially distributed model than the compartmental models (1.7 [1.3, 2.1] times higher).
The proposed axially distributed model provided accurate regional estimates of MBF. The axially distributed model estimated blood flow with more accuracy, but less precision, than the evaluated compartmental models.
KeywordsMyocardial blood flow cardiac PET quantitative PET dynamic imaging NH3
We are grateful to Barbara Lewellen for help with animal handling in the PET studies, to Eric Feigl for conversations about coronary physiology, to Wayne Lamm and Dowon An for microsphere processing, to UW Radiochemists Steve Shoner and Jeanne Link for NH3 preparation, to Erik Butterworth for development of the QPP software application, to Mike Bindschadler for manuscript review, and to Donna Cross and Satoshi Minoshima for assistance processing the imaging data. This research was supported by a grant from the Coulter Foundation and NIH Grants K25-HL086713, T15-HL088516, and RO1-EB08407.
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