Quantification of F-18 FDG uptake rate in the lung cancer using dynamic PET study

Objectives For the evaluation of F-18 FDG uptake on PET study, the value of SUV is widely used. The SUV are useful but they do not tell us the trends of the FDG uptake, increasing, decreasing or, becoming plateau. In this study, we investigated whether the trends of the FDG uptake in the lung tumor can be evaluated by Patlak-plot analysis with 1 hr dynamic PET scan. We explored the way to reduce the scan time of 1 hour to less than 30 minutes by estimating the area under curve (AUC) of the aorta as an arterial input function.

Methods Dynamic FDG-PET/CT scanning was performed on 25 cases of lung cancer patients. After image reconstruction, the TACs were determined from the aorta and the lung tumor. The clearance of F-18 FDG uptake, k-value, of the tumor was calculated by Patlak-plot analysis, and compared to SUVmax. To reduce the scan time, we compared the SUVmax of Aorta at the uptake time of 50 minutes (SUV50-Ao) with the AUC of the Aorta (AUC-Ao). The apparent k-value (AKV) of the tumor calculated from the values of SUV50-Ao was also compared with the k-value calculated from the values of AUC-Ao as an arterial input function.

Results The k-value of the lung tumor varied from 0.005 to 0.091 (min-1). The k-value showed strong correlation with SUVmax (r2=0.936). The linear relationship between the SUV50-Ao and the AUC-Ao was also observed (AUC-Ao=47.2 x SUV50-Ao+57.9, r2=0.84). The calculated AKV and the k-value showed strong linear correlation (AKV=0.96 x k-value; r2=0.99).

Conclusions The trends of the FDG uptake can be evaluated by calculating the k-value. The scan time can be reduced to less than 30 minutes with using linear equation converting SUV50-Ao to AUC-Ao. The calculated AKV could be a tolerable index of the trend of the FDG uptake for the clinical use