Room: Exhibit Hall | Forum 5
Purpose: To determine the optimal curve fitting method for the Toftâ€™s model to accurately quantify and detect radiation-induced changes in myocardial blood flow (MBF) parameter, Ktrans, measured with dual bolus Gd-DTPA based Dynamic Contrast Enhanced (DCE)-MRI.
Methods: Five canines received simultaneous N-13 Ammonia PET and dual bolus Gd-DTPA DCE-MR imaging at baseline, 1-week, 1, 3, 6, and 12-months after external beam irradiation targeted at the left anterior descending artery. Rest and adenosine-induced stress scans were conducted utilizing a fast gradient echo sequence on a Siemens 3T hybrid PET/MR scanner. The myocardium was contoured on the DCE-MRI dataset following a 17-segment-model. Since MBF = Ktrans/E, where E is the extraction fraction, the left ventricle was selected as the arterial input function (AIF). The myocardial tissue curves were fitted in MATLAB using Toftâ€™s model for both dual bolus and separate bolus techniques. Ktrans from blood plasma to extracellular/extravascular space was then calculated. N-13 Ammonia PET defined MBF was also calculated using 1-compartment model in FlowQuant (Ottawa Heart Institute, Canada). Paired t-tests were used to compare MBF between DCE-MRI and N-13 PET for each curve fitting technique.
Results: Statistical significance was observed between MBF obtained by separate bolus DCE-MR curve fitting technique and N-13 PET (p<0.05) in all artery supplied regions under both rest and stress conditions. This indicated an AIF signal saturation effect. However, MBF obtained by the dual bolus DCE-MR technique was not statistically different than N-13 PET defined MBF (p>0.05). Also, DCE-MR Ktrans rest and stress data trended differently after the 1-month timepoint.
Conclusion: Dual bolus curve fitting using Toftâ€™s model to determine myocardial Ktrans was necessary to accurately compute MBF with GD-DTPA MR imaging. However, we were not able to observe the same post-irradiation trends when comparing rest to stress MBF with both N13-PET and DCE-MR imaging.