Quantitative assessment of simultaneous F-18 FDG PET/MRI in patients with various types of hepatic tumors: Correlation between glucose metabolism and apparent diffusion coefficient

Abstract

Purpose: Metabolism and water diffusion may have a relationship or an effect on each other in the same tumor. Knowledge of their relationship could expand the understanding of tumor biology and serve the field of oncologic imaging. This study aimed to evaluate the relationship between metabolism and water diffusivity in hepatic tumors using a simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) system with F-18 fluorodeoxyglucose (FDG) and to reveal the metabolic and diffusional characteristics of each type of hepatic tumor.

Methods: Forty-one patients (mean age 63 ± 13 years, 31 male) with hepatic tumors (18 hepatocellular carcinoma [HCC], six cholangiocarcinoma [CCC], 10 metastatic tumors, one neuroendocrine malignancy, and six benign lesions) underwent FDG PET/MRI before treatment. Maximum standard uptake (SUVmax) values from FDG PET and the apparent diffusion coefficient (ADC) from the diffusion-weighted images were obtained for the tumor and their relationships were examined. We also investigated the difference in SUVmax and ADC for each type of tumor.

Results: SUVmax showed a negative correlation with ADC (r = -0.404, p = 0.009). The median of SUVmax was 3.22 in HCC, 6.99 in CCC, 6.30 in metastatic tumors, and 1.82 in benign lesions. The median of ADC was 1.039 × 10-3 mm/s2 in HCC, 1.148 × 10-3 mm/s2 in CCC, 0.876 × 10-3 mm/s2 in metastatic tumors, and 1.323 × 10-3 mm/s2 in benign lesions. SUVmax was higher in metastatic tumors than in benign lesions (p = 0.023). Metastatic tumors had a lower ADC than CCC (p = 0.039) and benign lesions (p = 0.004). HCC had a lower ADC than benign lesions, with a suggestive trend (p = 0.06).

Conclusion: Our results indicate that SUVmax is negatively correlated with ADC in hepatic tumors, and each group of tumors has different metabolic and water diffusivity characteristics. Evaluation of hepatic tumors by PET/MRI could be helpful in understanding tumor characteristics.

Fig 1. F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/ magnetic resonance (MR) images with region of interest (ROI).

(A–C) FDG PET/MR images of 85-year-old woman with cholangiocarcinoma; (D–F) 46-year-old man with hepatocellularcarcinoma; (G–I) 72-year-old man with hepatic metastasis from colon cancer. (A, D and G) Axial HASTE MRI images; (B, E and H) Fused images of FDG PET and HASTE; (C, F and I) ADC map. ROIs were manually drawn along the contour of the tumor except necrosis. HASTE, half-Fourier acquisition single-shot turbo spin-echo; ADC, apparent diffusion coefficient.

Fig 2. Inverse correlation between SUVmax and ADC.

Correlation analysis with scatter plots graph show moderate but significant inverse correlations between SUVmax and ADC (p = 0.009). SUVmax, maximum standard uptake value; ADC, apparent diffusion coefficient.

Fig 3. Box plots of SUVmax and ADC values of 41 hepatic tumors.

(A) Distribution of SUVmax in various types of hepatic tumors. SUVmax is higher in metastatic tumors than in benign lesions (p = 0.023). (B) Distribution of ADC in various types of hepatic tumors. Metastatic tumor shows lower ADC than benign lesions (p = 0.004) and CCC (p = 0.039). Each box plot shows median (thick lines), quartiles (upper and lower box boundaries), and extreme values (whiskers) within a category. ADC, apparent diffusion coefficient; CCC, cholangiocarcinoma; HCC, hepatocellular carcinoma.