In vivo measurement of human brain material properties under quasi-static loading

Abstract

Computational modelling of the brain requires accurate representation of the tissues concerned. Mechanical testing has numerous challenges, in particular for low strain rates, like neurosurgery, where redistribution of fluid is biomechanically important. A finite-element (FE) model was generated in FEBio, incorporating a spring element/fluid–structure interaction representation of the pia–arachnoid complex (PAC). The model was loaded to represent gravity in prone and supine positions. Material parameter identification and sensitivity analysis were performed using statistical software, comparing the FE results to human in vivo measurements. Results for the brain Ogden parameters µ , α and k yielded values of 670 Pa, −19 and 148 kPa, supporting values reported in the literature. Values of the order of 1.2 MPa and 7.7 kPa were obtained for stiffness of the pia mater and out-of-plane tensile stiffness of the PAC, respectively. Positional brain shift was found to be non-rigid and largely driven by redistribution of fluid within the tissue. To the best of our knowledge, this is the first study using in vivo human data and gravitational loading in order to estimate the material properties of intracranial tissues. This model could now be applied to reduce the impact of positional brain shift in stereotactic neurosurgery.

Rapid, non-invasive, in vivo measurement of tissue mechanical properties using gravitational loading and a nonlinear virtual fields method

“…In our previous study using the same finite-element model with data from a larger group of subjects [23], we found average values of μ = 670 Pa, K = 148 kPa and α = −19, which compare well with the present results, although K was lower with much more uncertainty. It was possible to estimate all three parameters, but the present method quantified K much more precisely and enabled a systematic error analysis which revealed uncertainty in μ and α.…”

Fabrication of a positional brain shift phantom through the utilization of the frozen intermediate hydrogel state

“…However, given the small strains involved in PBS, the brain shift resulting from fluid flow is likely to minimal. This is supported by the fact that Bennion et al (2022) was able to reproduce PBS in a computational model using a purely hyperelastic material model with no capacity for fluid flow.…”

“…Yet, while models have been produced to study other neurosurgical brain shift events, such as pneumocephalus mediated brain shift (PMBS) (Skrinjar et al, 2002;Sun et al, 2014;Forte et al, 2018) or craniotomy mediated brain shift (CMBS) (Clatz et al, 2003;Hu et al, 2007;Bilger et al, 2011), no models have been produced for the study of PBS. To address this, at Cardiff University two complimentary projects have been underway to develop a pair of synthetic and computational (Bennion et al, 2022) models. This is in addition to a third project which seeks to develop better methods to characterise PBS in vivo with MRI (Zappalá et al, 2021).…”

Fabrication of a Positional Brain Shift Phantom Through the Utilization of the Frozen Intermediate Hydrogel State

“…However, given the small strains involved in PBS, the brain shift resulting from fluid flow is likely to minimal. This is supported by the fact that Bennion et al 2022 was able to reproduce PBS in a computational model using a purely hyperelastic material model with no capacity for fluid flow [10].…”

“…Yet, while models have been produced to study other neurosurgical J o u r n a l P r e -p r o o f brain shift events, such as pneumocephalus mediated brain shift (PMBS) [11][12][13] or craniotomy mediated brain shift (CMBS) [14][15][16], no models have been produced for the study of PBS. To address this, at Cardiff University two complimentary projects have been underway to develop a pair of synthetic and computational [10] models. This is in addition to a third project which seeks to develop better methods to characterise PBS in vivo with MRI [9].…”