Anatomical and functional volume concordance between FDG PET, and T2 and diffusion-weighted MRI for cervical cancer: a hybrid PET/MR study

To evaluate the concordance among 18F-FDG PET imaging, MR T2-weighted (T2-W) imaging and apparent diffusion coefficient (ADC) maps with diffusion-weighted (DW) imaging in cervical cancer using hybrid whole-body PET/MR. This study prospectively included 35 patients with cervical cancer who underwent pretreatment 18F-FDG PET/MR imaging. 18F-FDG PET and MR images were fused using standard software. The percent of the maximum standardized uptake values (SUVmax) was used to contour tumours on PET images, and volumes were calculated automatically. Tumour volumes measured on T2-W and DW images were calculated with standard techniques of tumour area multiplied by the slice profile. Parametric statistics were used for data analysis. FDG PET tumour volumes calculated using SUVmax (14.30 ± 4.70) and T2-W imaging volume (33.81 ± 27.32 cm3) were similar (P > 0.05) at 35 % and 40 % of SUVmax (32.91 ± 18.90 cm3 and 27.56 ± 17.19 cm3 respectively) and significantly correlated (P < 0.001; r = 0.735 and 0.766). The mean DW volume was 30.48 ± 22.41 cm3. DW volumes were not significantly different from FDG PET volumes at either 35 % SUVmax or 40 % SUVmax or from T2-W imaging volumes (P > 0.05). PET subvolumes with increasing SUVmax cut-off percentage showed an inverse change in mean ADC values on DW imaging (P < 0.001, ANOVA). Hybrid PET/MR showed strong volume concordance between FDG PET, and T2-W and DW imaging in cervical cancer. Cut-off at 35 % or 40 % of SUVmax is recommended for 18F-FDG PET/MR SUV-based tumour volume estimation. The linear tumour subvolume concordance between FDG PET and DW imaging demonstrates individual regional concordance of metabolic activity and cell density. (orig.)