Intravoxel incoherent motion (IVIM) 3 T MRI for orbital lesion characterization

To determine the diagnostic accuracy of MRI intravoxel incoherent motion (IVIM) when characterizing orbital lesions, which is challenging due to a wide range of locations and histologic types. This IRB-approved prospective single-center study enrolled participants presenting with an orbital lesion undergoing a 3-T MRI prior to surgery from December 2015 to July 2019. An IVIM sequence with 15 b values ranging from 0 to 2000 s/mm${}^2$ was performed. Two neuroradiologists, blinded to clinical data, individually analyzed morphological MRIs. They drew one region of interest inside each orbital lesion, providing apparent diffusion coefficient (ADC), true diffusion coefficient (D), perfusion fraction (f), and pseudodiffusion coefficient (D*) values. T test, Mann-Whitney U test, and receiver operating characteristic curve analyses were performed to discriminate between orbital lesions and to determine the diagnostic accuracy of the IVIM parameters. One hundred fifty-six participants (84 women and 72 men, mean age 54.4 ± 17.5 years) with 167 orbital lesions (98/167 [59%] benign lesions including 54 orbital inflammations and 69/167 [41%] malignant lesions including 32 lymphomas) were included in the study. ADC and D were significantly lower in malignant than in benign lesions: 0.8 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [0.45] versus 1.04 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [0.33], p < 0.001, and 0.75 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [0.40] versus 0.98 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [0.42], p < 0.001, respectively. D* was significantly higher in malignant lesions than in benign ones: 12.8 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [20.17] versus 7.52 × 10${}^{\text{â}\text{ˆ}\text{’}3}$ mm${}^2$/s [7.57], p = 0.005. Area under curve was of 0.73, 0.74, 0.72, and 0.81 for ADC, D, D*, and a combination of D, f, and D*, respectively. Our study showed that IVIM might help better characterize orbital lesions.