Correlation Between Apparent Diffusion Coefficients and Standardized Uptake Values in Hybrid (18)F-FDG PET/MR: Preliminary Results in Rectal Cancer.
OBJECTIVE
Fluorine-18-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) and diffusion-weighted magnetic resonance imaging (DWI) share the same role in clinical oncology and it is feasible to obtain the standardized uptake value (SUV) and apparent diffusion coefficient (ADC) simultaneously by emerging the hybrid positron emission tomography/magnetic resonance (PET/MR). This study investigated the correlation between the ADCs of rectal cancer lesions and their SUVs derived from hybrid PET/MR.


METHODS
Nine patients with histologically proven rectal adenocarcinoma (5 men, 4 women; mean age, 70 ± 15.91 years) underwent torso (18)F-FDG PET/CT and regional hybrid (18)F-FDG PET/MR sequentially. A fixed threshold value of 40 % of maximum uptake was used to determine tumor volume of interest (VOI) on PET image; SUVmax, SUVpeak, and SUVmean were calculated automatically. A single freehand region of interest (ROI) was drawn on high b-value (b1000) DWI image and copied to corresponding ADC map to determine the ADCmean of rectal cancer lesion. Spearman's rank correlation coefficient (ρ) was calculated to determine the correlation between SUVs and ADC values.


RESULTS
SUVmax, SUVpeak, and SUVmean derived by hybrid PET/MR were 12.35 ± 4.66 (mean ± standard deviation), 9.66 ± 3.15 and 7.41 ± 2.54, respectively. The ADCmean value of rectal cancer lesions was 1.02 ± 0.08 × 10(-3)mm(2)/s. ADCmean was significantly and inversely correlated with SUV values (SUVmax, ρ = -0.95, p < 0.001; SUVpeak, ρ = -0.93, p < 0.001; SUVmean, ρ = -0.91, p = 0.001).


CONCLUSIONS
This preliminary hybrid PET/MR study demonstrates a significant inverse correlation exists between metabolic activity on (18)F-FDG PET and water diffusion on DWI in rectal cancer.
Department of Nuclear Medicine, Kyungpook National University Hospital, Daegu, Republic of Korea.
Ju Hye
JH
Jeong
Department of Nuclear medicine, Yeungnam University Hospital, 170, Hyeonchung-ro, Nam-gu, Daegu, 42415 Republic of Korea.
Ihn Ho
IH
Cho
Department of Nuclear medicine, Yeungnam University Hospital, 170, Hyeonchung-ro, Nam-gu, Daegu, 42415 Republic of Korea.
Kyung Ah
KA
Chun
Department of Nuclear medicine, Yeungnam University Hospital, 170, Hyeonchung-ro, Nam-gu, Daegu, 42415 Republic of Korea.
Eun Jung
EJ
Kong
Department of Nuclear medicine, Yeungnam University Hospital, 170, Hyeonchung-ro, Nam-gu, Daegu, 42415 Republic of Korea.
Sang Don
SD
Kwon
Department of Surgery, Yeungnam University Hospital, Daegu, Republic of Korea.
Jae Hwang
JH
Kim
Diffusion magnetic resonance imaging; Fluorodeoxyglucose F18; Multimodal Imaging; Positron-emission tomography; Rectal Neoplasms