Time-dependent diffusion MRI differentiates atypical from conventional uterine leiomyomas: A preliminary study

Preoperative differentiation of atypical from conventional uterine leiomyomas remains challenging on routine MRI due to overlapping morphological characteristics and signal heterogeneity related to degeneration or necrosis.

To evaluate whether time-dependent diffusion MRI (t_d-dMRI) derived from oscillating and pulsed gradient spin-echo (OGSE/PGSE) sequences improves differentiation between atypical and conventional uterine leiomyomas compared with routine MRI (T1WI, T2WI and DWI).

In this prospective study, 119 patients with pathologically confirmed uterine leiomyomas (78 conventional, 41 atypical) underwent both routine MRI and t_d-dMRI examinations. Relative signal intensity of lesion to gluteus muscle, and apparent diffusion coefficients (ADCs) were derived from routine MRI protocols, while microstructural parameters including intracellular fraction ( $f_{\mathrm{in}}$ ), cell diameter, extracellular diffusivity ( $D_{\mathrm{ex}}$ ), and cellularity, and ADCs at different diffusion times were estimated from t_d-dMRI modelling. Group differences were assessed using independent-sample tests, and diagnostic performances were evaluated with generalized linear models (GLMs) and receiver operating characteristic (ROC) analyses.

Atypical leiomyomas demonstrated significantly lower $f_{\mathrm{in}}$ (0.39 ± 0.10 vs. 0.49 ± 0.10, P < 0.001) and cellularity (4.12 ± 4.33 vs. 5.50 ± 4.34, P = 0.002), but higher $D_{\mathrm{ex}}$ (2.71 ± 0.64 vs. 2.09 ± 0.96 µm²/msec, P = 0.001) and ADCs at all diffusion times (all P < 0.001) compared with conventional leiomyomas. The t_d-dMRI-base_d GLM achieved an area under the ROC curve (AUC) of 0.84 (95% CI, 0.77-0.92), significantly higher than that of routine MRI characteristics (AUC 0.76, 95% CI 0.66-0.85; P = 0.037). The model combining both t_d-dMRI an_d routine MRI characteristics yielded additional improvement to that of routine MRI (AUC 0.86, 95% CI 0.79-0.93; P = 0.0075).

t_d-dMRI provides quantitative microstructural information that enables superior differentiation of atypical from conventional uterine leiomyomas compared with routine MRI. t_d-dMRI may serve as a promising adjunct for preoperative characterization and treatment planning of uterine leiomyomas.