Estimation of total liver uptake and liver uptake per unit of liver volume of Tc-99m(Sn)-N-pyridoxyl-5-methyltryptophan (Tc-99m-PMT) using SPECT

Total and regional liver function was evaluated by measuring total liver uptake (TLU) and liver uptake per unit of liver volume (LU/LV) of Tc-99m-PMT using SPECT. SPECT data were collected for 1 min starting at 4 min after bolus injection of Tc-99m-PMT. Attenuation and scatter correction for γ-rays was performed with a first order correction of Changs method using an attenuation coefficient of 0.115 cm-1, which was determined in our liver phantom experiment. The coefficient of variation over the corrected liver phantom images with a cut off level of 70% was 0.094. LU/LV is inversely proportional to the circulating blood volume so that LU/LV was multiplied by blood volume to be determined as Ui(4-5) index. Thirty six patients were examined. Normal value in 9 volunteers was 61.0±4.6% (mean±S.D.) and 196±19.8 ml·%/cm3 for TLU and mean Ui (4-5) index, respectively. TLU was well negatively correlated with blood retention rate (r=-0.847; p<0.001; n=33) and also well correlated with plasma disappearance rate of ICG (r=0.877; p<0.001; n=15), TLU had a good correlation with mean Ui(4-5) index (r=0.851; p<0.001; n=36), though there were some cases who had as much as twice differences is mean Ui(4-5) index against the same levels of the TLU. This method was considered to be valuable for clinical study because it provides both total liver function and regional function per unit of liver volume, including the information on appropriate liver volume and because it is a very simple and not time-consuming test, being to be performed along with a routine Tc-99m-PMT imaging. (author)