Cardiovascular transit times in mice by high temporal resolution microPET

In this study, we evaluated the temporal resolution of a new microPET system in mice. We then applied the high resolution capability for determining the cardiovascular transit time which is an important physiological parameter in the study of animal models of cardiovascular disease. Two groups of mice, group 1 (n=12) with high body weight and group 2 (n=10) with low body weight, were studied. Each mouse was injected with a 18F-deoxyglucose (FDG; 40-50 μL; 8-48 MBq) bolus and a list mode PET acquisition was started. MicroCT was performed for attenuation correction. We histogrammed the first 9 seconds of the list mode data into frames of 0.2 s-0.5 s duration. After the images were reconstructed and attenuation corrected, the ROIs were assigned to the following structures: vena cava, right and left ventricle blood pool (RV&LV), left lung and aorta. A time activity curve (VAC) of each ROI was generated. To correct for the recirculation, the end of each TAC was approximated by an exponential decay curve. The transit time (TT) was then calculated as the difference of the mean arrival times of the bolus in RV and LV. Short time frames of 0.3 s proved to be the best in terms of reducing noise and at the same being able to follow the rapid physiological processes. The peaks of the TACs showed good separation in various structures if the time spread of the bolus in the vena cava measured as full width of half maximum (FWHM) was shorter than 2 s. Group 1 had significantly (p<0.05) longer TT as expected than those of group 2.