Abstract
1501
Objectives: Partial volume effects caused by limited spatial resolution of conventional PET scanners result in underestimation of nuclide uptake in small tumors. Aim of the study was to evaluate the feasibility of small animal tumor imaging with the clinical PET scanner ECAT ECACT after partial volume correction. A dedicated small animal PET system (microPET focus 120) with high spatial resolution served as in vivo gold standard. Methods: Prior to the ECAT EXACT PET studies recovery coefficients for different sphere volumes from 0.5 to 16 ml were generated with phantom experiments (2D-mode, OSEM). For the following in vivo study DS-sarcoma cells were implanted on both hind foot dorsum of male Sprague-Dawley rats, after 7 to 14 days tumor volumes varied from approx. 0.5 to 2.1 ml. Dynamic FDG-PET was performed with the conventional scanner ECAT EXACT (5 MBq i.v., 2D-mode, 90 min., OSEM, n=16 tumors) and with microPET focus 120 (15 MBq i.v., 2D-mode, 60 min., OSEM, n=10 tumors). The animals were then sacrificed, tumors rapidly explanted, weighed and homogenized. Concentration of F-18-FDG was measured with a calibrated gamma counter and decay corrected. Ex vivo F-18-FDG concentration was compared with the mean tumor SUV of the PET data, in case of ECAT ECACT with additional tumor volume correction. Results: For the smallest tumor volume (0.48 ml) ECAT EXACT scanner underestimated actual F-18-activity up to 67%. Partial volume correction improved the correlation between the ROI-based tumor activity and the ex vivo measurements from r=0.70 to 0.97. These results were quite similar to the microPET experiments without partial volume correction: r=0.98. Conclusions: These data indicate that the application of partial volume correction allows to use a clinical PET system for global assessment of tumors ≥0.5 ml in small animals if no dedicated animal PET is available.
- Society of Nuclear Medicine, Inc.