Total-Body Quantitative Parametric Imaging of Early Kinetics of 18F-FDG.

Parametric imaging has been shown to provide better quantitation physiologically compared with SUV imaging in PET. With the increased sensitivity from a recently developed total-body PET scanner, whole-body scans with higher temporal resolution become possible for dynamic analysis and parametric imaging. In this paper, we focus on deriving the parameter k1 using compartmental modeling, and on developing a method to acquire whole-body FDG-PET parametric images using only the first 90 seconds of the post-injection scan data with the total-body PET system. Dynamic projections were acquired with a time interval of 1 second for the first 30 seconds and 2 seconds for the following minute. Image-derived input functions were acquired from the reconstructed dynamic sequences in the ascending aorta. The one-tissue compartment model with the total of 4 parameters (k1, k2, blood fraction, delay time) was used. A maximum-likelihood based estimation method was developed with the 1-tissue compartment model solution. The accuracy of the acquired parameters was compared with the ones estimated using a 2-tissue irreversible model with 1-hour long data. All four parametric images were successfully calculated using data from two volunteers. By comparing the time-activity-curves acquired from the volume of interests, it was shown that the parameters estimated using our method were able to predict the time-activity curves of the early dynamics of FDG in different organs. The time delay effects for different organs were also clearly visible in the reconstructed time delay image with delay variations as large as 40 seconds. The estimated parameters using both 90 seconds data and 1-hour long data were in good agreement for k1 and blood fraction, while a large difference of k2 was found between the 90 seconds and 1-hour data, suggesting k2 can’t be reliably estimated from the 90 second scan. We have shown that with the use of total-body PET and the increased sensitivity, it is possible to estimate parametric images based on the very early dynamics following FDG injection. The estimated k1 could potentially be used clinically as an indicator for identifying abnormalities.