Abstract
1691
Objectives: The low resolution of microPET combined with the small size of mice prove challenging for extraction of the input function, non-invasively, in mice studies. We propose a hybrid image-blood-sampling (HIBS) algorithm to derive the input function for quantification of microPET mice data. Methods: The HIBS algorithm derives the peak of the input function from the image while the tail is derived from 5-6 optimally-placed blood sampling points. The peak is subsequently corrected for recovery using a partial volume correction factor of 0.70 based on previous work. We use a Bezier interpolation algorithm to link the rightmost image peak data point to the leftmost blood sampling point. To assess the performance of HIBS, 4 mice underwent 60-minute microPET imaging sessions following a 0.40-0.50mCi bolus administration of 18FDG. In total, twenty one blood samples (BS) were obtained throughout the imaging session to compare against the HIBS method proposed within. MicroPET images were reconstructed using filter back projection (FBP) with a zoom of 2.75 on the heart. Volumetric regions of interest (VROI) were composed by drawing circular ROIs 3-pixels in diameter on 3-4 planes of the left ventricle. LV VROIs were subsequently corrected for partial volume as described above. To assess performance, we characterized the area-under-the-curve (AUC), bias between BS and HIBS, and performed kinetics simulations to characterize bias in parameter estimates when BS and HIBS are used as input functions. Results: The peak of the BS curve was dispersed in comparison to the HIBS derived curve due to temporal limitations and delay in blood sampling. As a result, in a few cases, parameters that characterize early kinetics were significantly (p>0.05) different from true parameters. In general, however, there were no significant (p<0.05) bias between HIBS and BS fitted values. In addition, differences in AUC were less than 10% and are mostly attributed to dispersion of the peak in BS. Conclusions: While non-invasive methods are fine-tuned for application to mice microPET images, the HIBS algorithm provides a simple alternative to blood sampling and allows for longitudinal and repeated imaging with minimal blood loss. We have successfully applied the method to mice and rat data.
- Society of Nuclear Medicine, Inc.