Comparison of methods for quantification of rCBF on the HRRT PET scanner using [<sup>15</sup>O]H<inf>2</inf>O

Abstract

The current study aimed to derive accurate esti­mates of regional cerebral blood flow (rCBF) from noisy dynamic [ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> O]H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O 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 [ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> O]H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O 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 autoradiogrpahic 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , 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.