Brain retraction is an important surgical technique that is used for lesion exposure in brain surgeries. However, in brain retraction, an excessive load may cause permanent damage to the brain. Therefore, the development of surgical simulators that can simulate the stress and force of brain reaction in advance of a real surgery is required.

In order to simulate brain retraction, a numerical calculation model of a viscoelastic body using the finite element method (FEM) was proposed. It is based on the generalized Maxwell model but considers the inertial term. The main advantage of including the inertial term is computational stability. The viscoelastic parameters were identified by the results of retraction experiments using whole porcine brains. Retraction experiments were performed with two retraction velocities, 1 mm/s and 10 mm/s. The parameters of the proposed model were identified by solving optimization problems using the retraction experimental results of the retraction velocity 10 mm/s. Retraction simulations (retraction velocity : 1 mm/s and 10 mm/s) were performed under the same conditions as in the experiments. The 3D simulation model was built from MRI data of a porcine brain. Comparing the simulation results and experimental data, it is confirmed that the viscoelastic model using the identified parameters simulated the brain retraction well.

Background and Aims : Non-obstructive azoospermia (NOA) is one of the most serious causes of male infertility. Microdissection testicular sperm extraction (MD-TESE) is a first-line therapy of NOA ; however, sperm retrieval rate from MD-TESE differs substantially between surgeons and is generally insufficient. To develop a new accessible method to identify seminiferous tubules with sperm in real time during MD-TESE, we have made a hypothesis that the hardness of seminiferous tubule wall is available as a quantitative index for the presence of sperm. In this study, as a first step, we determined the stiffness of the testis from an animal model of NOA using a measuring system that we designed.

Methods : Male Syrian hamster with bilateral experimental cryptorchidism was used as a NOA model. Stiffness of the testis was evaluated with two different indices of stiffness value : K_j (the stiffness value in a small interval) and K (the mean of K_j values) by using an indentation instrument with a micro force sensor.

Results : Hamster testis was confirmed to be valid as a dynamic model for physical measurements by checking the dependency of stiffness and viscosity on the reaction force generated in indentation procedure. Both stiffness values of the testis with cryptorchidism were significantly decreased compared with those of the control testis.

Conclusion : The results suggest that our system is useful for quantitative evaluation of testis stiffness. Testis hardness has promise for a new index for spermatogenesis. As the next step, we need this approach to permit measurement for seminiferous tubules.