Determination of cis-4-[18F][1]fluoro-L-proline (18F-FP) normal biodistribution in experiments optimized for hepatic uptake using dynamic and static PET/CT imaging.

1235 Purpose: Determination of cis-4-[18F][1]fluoro-L-proline (18F-FP) normal biodistribution in experiments optimized for hepatic uptake using dynamic and static PET/CT imaging. Objectives: Although cis-4-[18F][1]fluoro-L-proline (18F-FP) has previously been studied in other fibrotic processes, its use has not been evaluated for of fibrotic processes involving the liver. In this study, 18F-FP dose- and time- optimization experiments were performed to optimize hepatic uptake. Then, the biodistributions in normal liver and in the setting of alcoholic liver disease were computed. Methods: The biodistribution of 18F-FP was evaluated in liver, brain, lung, heart, spleen, kidney, bladder, stomach, pancreas, colon, thigh and spinal cord by drawing a region of interest (ROI) containing each organ/tissue and measuring nanocuries per cubic centimeter (nCi/cc) within the ROI. Biodistribution was computed in controls and in the setting of alcoholic liver disease. Results: HPLC demonstrated high 18F incorporation and high purity of synthesized 18F-FP. The liver had marked 18F-FP activity from the time of the initial imaging to 30 minutes, then washed out from the liver from 30-60 minutes but the liver tracer activity remained detectable until 120 minutes after injection. No visualization of tracer activity in the region of the gallbladder was identified during the imaging period. Heart had the greatest activity at the beginning of the imaging, followed by quick washout of tracer from the left ventricle after 30 minutes of imaging. Radiotracer activity in the region of the left ventricle is not significantly different between both periods of 30-60 minutes and 90-120 minutes. The highest overall activity was present in kidney (between 10-30 minutes) and bladder (between 20-120 minutes), which is depicted in Fig. 4A. The right side of the thigh was used for representation of muscular uptake of 18F-FP. Data showed relative stable muscle activity at time points from 30-60 minutes to 90-120 minutes. The tissues/organs with lowest uptake of 18F-FP were the spleen, lung and brain while stomach and colon showed slightly higher activity. Conclusions: An initial concern was that uptake in the spine region in 18F-FP PET images could be caused by free 18F tracer uptake as free 18F is a bone imaging radiotracer, which means that the 18F-FP radiotracer used in the study may be susceptible bone uptake-associated artifacts. PET/CT studies were performed with free 18F (in the form of 18F-NaF) for comparison with 18F-FP PET/CT imaging on the same animals in order to control for free 18F artifacts. While there was uptake of 18F-FP in the region of the spine, comparison with free 18F demonstrated a different distribution within the spine. The uptake in the spine region with free 18F PET/CT imaging was more prominent (Fig 4B-C) and localized within osseous structures of vertebral bodies. The uptake in the spine region with 18F-FP localized to the spinal canal] fibro-osseous compartments (best demonstrated on the sagittal views of MIP images), further confirming excellent incorporation of radioisotope 18F into 18F-FP in these experiments. Furthermore, there was no visualization of radiotracer uptake in the liver in free 18F PET imaging. Dash = Controls; Red line = Alcoholic liver disease Figure 2 Figure 3