A simplified method for quantification of hepatic blood perfusion was developed, using three-minute dynamic 18F-FDG PET or 11C-MG PET with blood sampling from only a peripheral artery, according to a study of pigs in the July issue of the Journal of Nuclear Medicine. Parametric K1 images were constructed and showed homogeneous blood perfusion in these normal livers.
According to the authors, there is an unmet clinical need for an imaging method for quantification of hepatic blood perfusion. Thus, in this study, Susanne Keiding, MD, from the PET Centre at Aarhus University Hospital in Aarhus, Denmark, and colleagues sought to develop and validate a PET method using blood-to-cell clearance ( K1) of 18F-FDG, 3-O-11C-methylglucose (11C-MG), or 2-18F-fluoro-2-deoxy-D-galactose (18F-FDGal) as a measure of hepatic blood perfusion without the need for portal venous blood samples.
The researchers noted that they aimed to “make the method as simple as possible with the prospect of future application to clinical studies.” For this purpose, they examined the possibility of using a three-minute data acquisition and a model-derived dual input calculated from measurements of radioactivity concentrations in a peripheral artery.
Pigs (40 kg) underwent dynamic PET of the liver with 18F-FDG, 11C-MG or 18F-FDGal with simultaneous measurements of time–activity curves in blood sampled from a femoral artery and the portal vein (PV); blood flow rates were measured in the hepatic artery (HA) and PV by transit-time flow meters.
Then, Keiding et al compared two input functions: a measured dual input and a model-derived dual input, the latter with the PV time–activity curve estimated from the measured arterial time–activity curve and a previously validated one-parametric PV model. They estimated K1 for each tracer by fitting compartmental models to the data, comparing three-minute and 60-minute data acquisitions and the two dual-input time–activity curves.
Agreement between K1 estimated using the measured and the model-derived dual input was “good for all three tracers,” the authors wrote. For 18F-FDG and 11C-MG, K1 (three-minute data acquisition, model-derived dual input and one-tissue compartmental model) correlated to the measured blood perfusion. For 18F-FDGal, the correlation was not significant, they reported.
When regarding 18F-FDG and 11C-MG as double determinations in the six pigs that underwent PET with both tracers, the researchers found a “highly significant correlation” between changes in hepatic blood perfusion, Q and changes in K1.
Based on their results, Keiding and colleagues concluded that they had developed and validated a simplified method to quantify and image blood perfusion in normal pig livers using a three-minute dynamic PET acquisition after intravenous injection of 11C-MG or 18F-FDG, the latter being a commonly available PET tracer.