A method and system for registering a pre-operative 3D medical image volume of a target organ to intra-operative ultrasound images is disclosed. An intra-operative 3D B-mode ultrasound volume and an intra-operative 3D ultrasound elastography volume are acquired. Patient-specific boundary conditions for a biomechanical tissue model of a target organ are determined using the intra-operative 3D B-mode volume. Patient-specific material properties for the biomechanical tissue model of the target organ are determined using the 3D ultrasound elastography volume. The target organ in the pre-operative 3D medical image volume is deformed using the biomechanical tissue model with the patient-specific material properties with the deformation of the target organ in the pre-operative 3D medical image volume constrained by the patient-specific boundary conditions.
