Correlation of minimum apparent diffusion coefficient with maximum standardized uptake on fluorodeoxyglucose PET-CT in patients with rectal adenocarcinoma

PURPOSE The aim of this study was to retrospectively assess the correlation between minimum apparent diffusion coefficient (ADC(min)) values obtained from diffusion-weighted magnetic resonance imaging (MRI) and maximum standardized uptake values (SUVmax) obtained from positron emission tomography-computed tomography (PET-CT) in rectal cancer. MATERIALS AND METHODS Forty-one patients with pathologically confirmed rectal adenocarcinoma were included in this study. For preoperative staging, PET-CT and pelvic MRI with diffusion-weighted imaging were performed within one week (mean time interval, 3 +/- 1 day). For ADC measurements, the region of interest (ROI) was manually drawn along the border of each hyperintense tumor on b=1000 s/mm(2) images. After repeating this procedure on each consecutive tumor-containing slice to cover the entire tumoral area, ROIs were copied to ADC maps. ADC(min) was determined as the lowest ADC value among all ROIs in each tumor. For SUVmax measurements, whole-body images were assessed visually on transaxial, sagittal, and coronal images. ROIs were determined from the lesions observed on each slice, and SUVmax values were calculated automatically. The mean values of ADC(min) and SUVmax were compared using Spearman's test. RESULTS The mean ADC(min) was 0.62 +/- 0.19x10(-3) mm(2)/s (range, 0.368-1.227x10(-3) 3 mm(2)/s), the mean SUVmax was 20.07 +/- 9.3 (range, 4.3-49.5). A significant negative correlation was found between ADC(min) and SUVmax (r=-0.347; P = 0.026). CONCLUSION There was a significant negative correlation between the ADC(min) and SUVmax values in rectal adenocarcinomas.