Mechanical properties of porcine brain tissue in vivo and ex vivo estimated by MR elastography

Abstract

The mechanical properties of brain tissue in vivo determine the response of the brain to rapid skull acceleration. These properties are thus of great interest to the developers of mathematical models of traumatic brain injury (TBI) or neurosurgical simulations. Animal models provide valuable insight that can improve TBI modeling. In this study we compare estimates of mechanical properties of the Yucatan mini-pig brain in vivo and ex vivo using magnetic resonance elastography (MRE) at multiple frequencies. MRE allows estimations of properties in soft tissue, either in vivo or ex vivo, by imaging harmonic shear wave propagation. Most direct measurements of brain mechanical properties have been performed using samples of brain tissue ex vivo. It has been observed that direct estimates of brain mechanical properties depend on the frequency and amplitude of loading, as well as the time post-mortem and condition of the sample. Using MRE in the same animals at overlapping frequencies, we observe that porcine brain tissue in vivo appears stiffer than porcine brain tissue samples ex vivo at frequencies of 100 Hz and 125 Hz, but measurements show closer agreement at lower frequencies.

Frequency dependent viscoelastic properties of porcine brain tissue

“…This finding is consistent with previous results for porcine bladder [34], mitral valve leaflet [21], and human/porcine brain [42], for the latter magnetic resonance elastography (MRE) was performed to describe the material properties. Loss stiffness of porcine brain exhibited an increasing trend with frequency; a similar tendency has been found in brain tissue by dynamic testing in shear [17,43] and MRE methods [44]. In spite of differences in testing devices and experimental conditions, the general trends were consistent with previous studies.…”

Ultra-sensitive measurement of brain penetration mechanics and blood vessel rupture with microscale probes

“…1f). Both the curve shape and magnitude of the prepenetration phase are very similar between in vivo and ex vivo tests, which agrees with previous indentation measurements suggesting they have similar mechanical properties [18][19][20] . Surprisingly, as the insertion force to drive the wire deeper into tissue in vivo after pia-penetration was constant as a function of depth.…”

Fifty Shades of Brain: A Review on the Mechanical Testing and Modeling of Brain Tissue

“…These observations agree well with measurements using ultrasound elastography, where the shear modulus in vivo was about 47% higher than that given by ex vivo measurements [105]. A recent study using magnetic resonance elastography confirms that porcine brain tissue appears stiffer in vivo than ex vivo at frequencies of 100 and 125 Hz [72]. At lower frequencies, however, they found closer agreement between ex vivo and in vivo measurements.…”