Time‐dependent diffusion MRI to distinguish malignant from benign head and neck tumors

BACKGROUND There is growing interest in the effect of diffusion time on apparent diffusion coefficient (ADC) values in cancers; however, little evidence exists regarding its utility to differentiate malignant from benign head and neck tumors. PURPOSE To investigate the utility of ADC value changes in distinguishing between malignant and benign head and neck tumors using the different diffusion times obtained from oscillating gradient spin-echo (OGSE) and pulsed gradient spin-echo (PGSE) MRI sequences. STUDY TYPE Prospective. SUBJECTS Thirty-one consecutive patients with suspected head and neck tumors and a phantom. FIELD STRENGTH/SEQUENCE 3T MRI with diffusion-weighted imaging (DWI) using OGSE (effective diffusion time: 4.3 msec) and PGSE (effective diffusion time: 82.6 msec) sequences and b-values of 0 and 700 s/mm2 . ASSESSMENT ADC values using OGSE (ADCOGSE ) and PGSE (ADCPGSE ) and relative ADC value changes between ADCOGSE and ADCPGSE . STATISTICAL TESTS Wilcoxon test, Mann-Whitney test, and McNemar test. RESULTS Relative ADC changes for each polyvinylpyrrolidone (PVP) and water in the phantom between OGSE and PGSE sequences were small (relative ADC change within 0.6%). Malignant tumors had significantly smaller ADCOGSE and ADCPGSE values than benign tumors (P < 0.001 and < 0.0001, respectively). Significantly larger relative ADC changes were observed in malignant compared with benign head and neck tumors (P < 0.0001). ADCPGSE values were significantly lower than ADCOGSE values in both malignant and benign head and neck tumors (0.97 vs. 1.28 × 10-3 mm2 /s: P < 0.0001 and 1.93 vs. 1.99 × 10-3 mm2 /s: P = 0.0056, respectively). Relative ADC change and ADCPGSE tended to have higher diagnostic performance than ADCOGSE , with area under the curve (AUC) values of 0.97, 0.96, and 0.89, respectively. DATA CONCLUSION ADC values obtained using the PGSE sequence were lower than those obtained with OGSE. This difference was larger for malignant than benign tumors, suggesting differences in tissue structure (diffusion hindrance) or cell permeability, revealed by changes in diffusion time. The results underline the potential importance of reporting diffusion time for interpretation of head and neck diffusion MRI. LEVEL OF EVIDENCE 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:88-95.