Validation of myocardial perfusion reserve measurements using regularized factor images of H₂¹⁵O dynamic PET scans

The use of H₂¹⁵O PET scans for the measurement of myocardial perfusion reserve (MPR) has been validated in both animal models and humans. Nevertheless, this protocol requires cumbersome acquisitions such as C¹⁵O inhalation or ¹⁸F-FDG injection to obtain images suitable for determining myocardial regions of interest. Regularized factor analysis is an alternative method proposed to define myocardial contours directly from H₂¹⁵O studies without any C¹⁵O or FDG scan. The study validates this method by comparing the MPR obtained by the regularized factor analysis with the coronary flow reserve (CFR) obtained by intracoronary Doppler as well as with the MPR obtained by an FDG acquisition. Methods: Ten healthy volunteers and 10 patients with ischemic cardiopathy or idiopathic dilated cardiomyopathy were investigated. The CFR of patients was measured sonographically using a Doppler catheter tip placed into the proximal left anterior descending artery. The mean velocity was recorded at baseline and after dipyridamole administration. All subjects underwent PET imaging, including 2 H₂¹⁵O myocardial perfusion studies at baseline and after dipyridamole infusion, followed by an FDG acquisition. Dynamic H₂¹⁵O scans were processed by regularized factor analysis. Left ventricular cavity and anteroseptal myocardial regions of interest were drawn independently on regularized factor images and on FDG images. Myocardial blood flow (MBF) and MPR were estimated by fitting the H₂¹⁵O time-activity curves with a compartmental model. Results: In patients, no significant difference was observed among the 3 methods of measurement-Doppler CFR, 1.73 ± 0.57; regularized factor analysis MPR, 1.71 ± 0.68; FDG MPR, 1.83 ± 0.49-using a Friedman 2-way ANOVA by ranks. MPR measured with the regularized factor images correlated significantly with CFR (y = 1.1 7x - 0.30; r = 0.97). In the global population, the regularized factor analysis MPR and FDG MPR correlated strongly (y = 0.99x; r = 0.93). Interoperator repeatability on regularized factor images was 0.126 mL/min/g for rest MBF, 0.38 mL/min/g for stress MBF, and 0.34 for MPR (19% of mean MPR). Conclusion: Regularized factor analysis provides well-defined myocardial images from H₂¹⁵O dynamic scans, permitting an accurate and simple measurement of MPR. The method reduces exposure to radiation and examination time and lowers the cost of MPR protocols using a PET scanner.