Correlation of SUVand tumor to blood standard uptake ratio (SUR) with the metabolic uptake rate derived from quantitative dual time point measurements.

Aim: Determination of tumor SUV is widely used for quantitative assessment of tumor metabolism in FDG-PET. However, the SUV approach has several well known limitations compromising its ability to act as a surrogate parameter of glucose consumption. Recently, we have shown that SUR overcomes most of these limitations as long as FDG kinetics in the target structure can be considered irreversible [1,2]. Excellent linear correlation of SUR and Km from Patlak analysis was found using dynamic imaging of liver metastases. However, due to the perfectly standardized uptake period used for SUR determination and the comparatively short uptake period these results are not directly applicable to clinical whole body examinations, in which the uptake periods often vary considerably. Therefore, the aim of this work was to investigate the correlation of SUR and Km in clinical whole body scans, where Km was approximated by Ks derived from dual time point (DTP) measurements [3]. Methods: DTP FDG-PET/CT was performed in 76 consecutive patients with histologically proven NSCLC. In the PET images the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV the aorta was delineated manually in the attenuation CT. The aorta ROI was transferred to the PET image. Blood SUV was computed as the mean value of the aorta ROI. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values were scan-time-corrected to 60 min p.i. as described in [2]. Metabolic uptake rate Ks was computed similar to the procedure in [3]. The correlation of SUV and SUR with Ks was investigated. Results: There was highly significant correlation of SUR and Ks ( R²=0.9). However, the correlation coefficient appeared somewhat lower than previous results obtained from dynamic imaging and standardized uptake times (R²=0.96 [1]). As expected, SUV showed markedly lower correlation with Ks than SUR (R²=0.76). Conclusion: Our results show that in clinical whole body PET the correlation of uptake values with the metabolic trapping rate can be improved notably by blood normalization and scan-time-correction. Furthermore, the high correlation of SUR with Ks indicates that for histologically unambigous tumor lesions DTP do not provide added value in comparison to the SUR approach. Literature: [1] EJNMMI Res 2013,3:77 [2] EJNMMI Res 2014,4:18 [3] EJNMMI Res 2012,3:16