The high-resolution research tomograph (HRRT) is a dedicated human brain PET scanner. The purpose of this study was to compare the quantitative accuracy of the HRRT with that of the clinical HR+ PET scanner and to assess effects of differences in spatial resolution between both scanners ( approximately 2.7 mm and approximately 7.0 mm for HRRT and HR+, respectively).
Methods: Paired (11)C-flumazenil scans of 7 healthy volunteers were assessed. For each volunteer, dynamic scans (including arterial sampling) were acquired on both scanners on the same day, thereby minimizing intersubject variability. Volume of distribution was generated using Logan plot analysis with plasma input. In addition, other plasma input, reference tissue (with pons as the reference tissue input), and parametric methods were included in the interscanner comparison.
Results: Logan volume-of-distribution analysis of HRRT data showed higher values than that of HR+ data (slope with the intercept fixed at the origin of 1.14 +/- 0.10 to 1.19 +/- 0.10, depending on the HRRT reconstruction method used). Smoothing HRRT reconstructions with a 6-mm full width at half maximum gaussian kernel reduced this slope toward the line of identity (1.04 +/- 0.11 to 1.07 +/- 0.11), retaining good correlation between HR+ and HRRT data (r, approximately 0.98). Similar trends were observed for other plasma input, reference tissue, and parametric methods. However, after reference matching the reference tissue models showed lower HRRT kinetic parameter values than HR+ values (slope with fixed intercept, 0.90 +/- 0.10 to 0.94 +/- 0.13).
Conclusion: Higher values of pharmacokinetic parameter values, obtained from HRRT versus HR+ PET studies, indicate improved HRRT PET quantification primarily due to a reduction in partial-volume effects.