Comparison of methods for quantification of rCBF on the HRRT PET scanner using [15O]H2O

The current study aimed to derive accurate estimates of regional cerebral blood flow (rCBF) from noisy dynamic [¹⁵O]H₂O PET images acquired on the High Resolution Research Tomograph (HRRT), whilst retaining the high spatial resolution of this scanner (2-3 mm) in parametric images. We compared the PET autoradiographic and the generalised linear least squares (GLLS) methods to the non-linear least squares (NLLS) method for rCBF estimation. Six healthy volunteers underwent two [¹⁵O]H₂O PET scans which included continuous arterial blood sampling. rCBF estimates were obtained from different methods of image reconstruction: 3DRP, OP-OSEM, and RM-OP-OSEM which includes a resolution model. A range of filters (3D Gaussian, 0-6 mm FWHM) were considered, as were a range of accumulation times (40-120 s) in the case of the autoradiographic method. Whole-brain rCBF values were found to be relatively insensitive to the method of reconstruction and rCBF quantification. The average whole-brain gray matter (GM) rCBF for 3DRP reconstruction and NLLS was 0.44±0.03 mL min cm^-3, in agreement with literature values. Similar values were obtained from other methods. For generation of parametric images using GLLS or the autoradiographic method, a filter of ≥4 mm was required in order to suppress noise in the PET images which can otherwise produce large biases in the rCBF estimates.