Intravoxel incoherent motion (IVIM) MRI-derived masseter muscle characteristics

Background: To use intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) to evaluate the masseter muscle and tumors in patients with head and neck cancer (HNC) and to compare them with those of normal controls. Methods: The study involved 16 normal controls and 54 patients with HNC (29 newly diagnosed and 25 posttreatment cases) examined using a 3.0T MRI with a 20-channel head and neck coil. IVIM scans, incorporating six b-values in three orthogonal directions, were conducted using a readout-segmented echo-planar sequence. The diffusion coefficient (D), perfusion fraction (f), and pseudodiffusion coefficient (D*) were derived to assess the diffusion and perfusion alterations in the masseter muscles and HNC lesions. Results: The masseter muscle f values significantly differed between the patients with newly diagnosed HNC and the normal controls (p < 0.05); no significant differences in remaining D, D*, and f values were observed between the three groups (p > 0.05). The masseter muscle volumes in the newly diagnosed HNC and posttreatment patients were significantly smaller than those in the normal controls (all p < 0.05). The D and f values of the bilateral masseter muscles in the patients with newly diagnosed HNC were significantly higher than those in the primary cancer lesions (p < 0.05). Conclusions: Our study highlights the potential of IVIM parameters for the evaluation of masseter muscles in patients with HNC, with elevated f values on the ipsilateral side of primary tumors and bilaterally increased D and f values. The clinical implications and underlying mechanisms of these findings of distinct perfusion changes warrant further exploration.