The Effects of Young's Modulus on Predicting Prostate Deformation for MRI-Guided Interventions

Accuracy of image-guided prostate interventions can be improved by warping (i.e., nonrigid registration) of high-quality multimodal preoperative magnetic resonance images to the intraoperative prostate geometry. Patient-specific biomechanical models have been applied in several studies when predicting the prostate intraoperative deformations for such warping. Obtaining exact patient-specific information about the stress parameter (e. g., Young's modulus) of the prostate peripheral zone (PZ) and central gland (CG) for such models remains an unsolved problem. In this study, we investigated the effects of ratio of Young's modulus of the central gland E-CG to the peripheral zone E-PZ when predicting the prostate intraoperative deformation for ten cases of prostate brachytherapy. The patient-specific prostate models were implemented by means of the specialized nonlinear finite element procedures that utilize total Lagrangian formulation and explicit integration in time domain. The loading was defined by prescribing deformations on the prostate outer surface. The neo-Hookean hyperelastic constitutive model was applied to simulate the PZ and CG mechanical responses. The PZ to CG Young's modulus ratio E-CG: E-PZ was varied between 1:1 (upper bound of the literature data) and 1:40 (lower bound of the literature data). The study indicates that the predicted prostate intraoperative deformations and results of the prostate MRIs nonrigid registration obtained using the predicted deformations depend very weakly on the E-CG: E-PZ ratio.