A model for simulation and patient-specific visualization of the tissue volume of influence during brain microdialysis

Microdialysis can be used in parallel to deep brain stimulation (DBS) to relate biochemical changes to the clinical outcome. The aim of the study was to use the finite element method to predict the tissue volume of influence (TVI_max) and its cross-sectional radius (r _TVImax) when using brain microdialysis, and visualize the TVI_max in relation to patient anatomy. An equation based on Fick’s law was used to simulate the TVI_max. Factorial design and regression analysis were used to investigate the impact of the diffusion coefficient, tortuosity and loss rate on the r _TVImax. A calf brain tissue experiment was performed to further evaluate these parameters. The model was implemented with pre-(MRI) and post-(CT) operative patient images for simulation of the TVI_max for four patients undergoing microdialysis in parallel to DBS. Using physiologically relevant parameter values, the r _TVImax for analytes with a diffusion coefficient D = 7.5 × 10⁻⁶ cm²/s was estimated to 0.85 ± 0.25 mm. The simulations showed agreement with experimental data. Due to an implanted gold thread, the catheter positions were visible in the post-operative images. The TVI_max was visualized for each catheter. The biochemical changes could thereby be related to their anatomical origin, facilitating interpretation of results.