Quantification of myocardial blood flow using N-13-ammonia and PET: Comparison of tracer models

Several tracer kinetic methods have been proposed for quantification of reg ional myocardia[ blood flow (MBF) with N-13-ammonia and PET. Merits and lim itations specific to each approach, however, generally are not clear, becau se they have not been evaluated in the same experimental environment. There fore, we compared six different commonly used methods (11 modifications) to characterize the accuracy of each approach. The methods included the two-p arameter model (method 1), the modified two-parameter model (method 2), the four-parameter model (method 3), the graphical analysis (method 4), the fi rst-pass extraction method (method 5) and the dose uptake index (DUI; metho d 6). Methods: Eleven studies in four dogs, 16 studies in eight healthy hum an volunteers and 14 studies in seven patients were performed using N-13-am monia and PET. MBF in dogs was varied with dipyridamole and coronary occlus ions and was measured independently and simultaneously with microspheres. V olunteers and patients were studied at baseline and after dipyridamole. MBF and DUI were estimated using a time-activity curve (Q(i)[t]) derived from dynamic images and regions of interest (ROIs) and using the six methods. DU I was defined as Q(i)(t = 2 min) x weight/dose. Results: MBF estimated by m ethods 1-5 correlated well with microsphere MBF in dogs. MBF estimates by m ethod 1 correlated well with those by methods 2, 4 and 5 and to a lesser de gree with those by method 3 in both dog and human studies. DUI correlated p oorly with MBF by microspheres and by methods 1-5 in both dog and human stu dies. MBF estimates by method 3 showed larger dispersion (SD/mean flow) and higher sensitivity to metabolites correction in arterial blood than those by methods 1, 2, 4 and 5. Conclusion: MBF can be measured accurately using N-13-ammonia PET and tracer kinetic methods. DUI is a poor indicator of MBF values. The results indicate that preference should be given to the two-pa rameter model, incorporating geometrical ROI representation (method 2) amon g the compartment models, and to the graphical analysis (method 4) among th e noncompartmental approaches.