Tissue Characterization of Uterine Fibroids With an Intravoxel Incoherent Motion Model: The Need for T2 Correction

Background: Diminished signal intensity of uterine fibroids in T-2-weighted images is routinely used as a qualitative marker of fibroid hypoperfusion. However, quantitative classification of fibroid perfusion with intravoxel incoherent motion (IVIM) model-based metrics is not yet clinically accepted. Purpose: To investigate the influence of T-2 correction on the estimation of IVIM model parameters for characterizing uterine fibroid tissue. Study Type: Prospective. Population: Fourteen women with 41 fibroids (12 Type I and 29 Type II, per Funaki classification) underwent diffusion-weighted imaging and T-2 mapping. Field Strength: Diffusion-weighted images (b values: 0, 20, 40, 60, 100, 200, 400, 600, 800, 1000 s/mm(2)) and T-2 maps were obtained at 1.5T. Assessment: The effect of uterine fibroid T-2 variation on IVIM model parameters (diffusion coefficient, perfusion coefficient, and perfusion volume fraction) were numerically modeled and experimentally evaluated without (D, D*, f) and with (D-c, D-c*, f(c)) T-2 correction. The relationship of T-2 with D and the T-2-corrected perfusion volume fraction (f(c)) was also examined. Statistical Test: D-values and f-values estimated with and without T-2 correction were compared by using a two-tailed Student's t-test. Results: Type II fibroids had higher D and f than Type I fibroids, but the differences were not significant (Type I vs. Type II, D: 0.830.20 vs. 0.800.25mm(2)/s, P = 0.78; f: 23.644.87% vs. 25.277.46%, P = 0.49). For Type I and Type II fibroids, f(c) was lower than f, and f(c) of Type II fibroids was significantly higher than that of Type I fibroids (Type I vs. Type II, f(c): 7.80 +/- 1.88% vs. 11.82 +/- 4.13%, P=0.003). Both D and f(c) exponentially increased with the increase of fibroid T-2 as functions: D-c(T-2) = -1.52x10(-3) . e(-3.42T2/290) + 1.84x10(-3) and f(c)(T-2) = -0.2336 . e(-3.217T2/290)+0.2269, respectively. D asymptotically approached 1.79 x 10(-3) mm(2)/s, and f(c) approached 21.74%. Data Conclusion: T-2 correction is important when using IVIM-based models to characterize uterine fibroid tissue.