Validation of an axially distributed model for quantification of myocardial blood flow using ¹³N-ammonia PET.
BACKGROUND
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.


METHODS
We validated PET-derived flow estimates with microsphere studies in 19 (9 rest, 10 stress) studies in five dogs. The radiotracer, (13)N-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.


RESULTS
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).


CONCLUSIONS
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.
Department of Radiology, University of Washington, 4000 15th Ave NE, PO Box 357987, Seattle, WA 98195-6004, USA. aalessio@uw.edu
Adam M
AM
Alessio
James B
JB
Bassingthwaighte
Robb
R
Glenny
James H
JH
Caldwell
D000641:Ammonia; D000818:Animals; D016477:Artifacts; D003326:Coronary Circulation / Q000502:physiology*; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging; D006439:Hemodynamics; D008863:Microspheres; D008955:Models, Cardiovascular; D009206:Myocardium / Q000473:pathology*; D009590:Nitrogen Radioisotopes; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D019275:Radiopharmaceuticals; D013997:Time Factors
D009590:Nitrogen Radioisotopes; D019275:Radiopharmaceuticals; D000641:Ammonia