Objective
To establish the magnitude change and inter-reader reliability of Liver SULmean in dual time point imaging at 1 and 2 hours and 1 and 4 hours.
Methods
Early and Delayed FDG PET/CT scans were included for 28 patients (13 males and 15 females) who had normal liver by CT or US. The average uptake time between the early and delayed scans were 55 minutes (range 44-69) for pancreatic adenocarcinoma patients (n = 19) and 184 minutes (range 140-197) for neurofibromatosis (NF) patients (n = 9). 30-mm- diameter spherical VOI was placed within the right lobe of the liver above, below, and at the level of the main portal vein by two independent readers. Correlation coefficients, Analysis of variance, intraclass correlation coefficient (ICC), and Bland-Altman analysis were performed.
Results
The mean liver SULmean was between 1.39 and 1.42 and between 1.28 and 1.3 in early and delayed images, respectively (p = 0.001). There is time dependent reduction in the mean Liver SULmean at 2 hour (7-8%) and four hour uptake time (15-21%), compared to one hour. The correlation coefficient between delayed uptake time and Liver SULmean reduction is 0.39 to 0.41 at the upper aspect of liver. The ICC for two readers varied between 0.997 and 0.998 and between 0.995 and 0.999 in early and delayed images, respectively (p=0.001).
Conclusion
There is time dependent reduction of mean Liver SULmean, about 7-8% within the clinically relevant FDG uptake time, in the same patient with excellent inter-reader agreement in early and delayed images within the right lobe of the liver. Therefore Liver SULmean could represent a useful reference parameter in quantitative analysis of dual-phase FDG PET/CT in malignancy or atypical infection/inflammatory disease. Furthermore, it may be suitable as normalization factor in currently available formulae quantifying therapy response on PET imaging.