@article{chandrasekaran_santibanez_long_nichols_kait_bruegge_bass_pinton_2024, title={Shear shock wave injury<i> in</i><i> vivo:</i> High frame-rate ultrasound observation and histological assessment}, volume={166}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2024.112021}, abstractNote={Using high frame-rate ultrasound and ¡1μm sensitive motion tracking we previously showed that shear waves at the surface of ex vivo and in situ brains develop into shear shock waves deep inside the brain, with destructive local accelerations. However post-mortem tissue cannot develop injuries and has different viscoelastodynamic behavior from in vivo tissue. Here we present the ultrasonic measurement of the high-rate shear shock biomechanics in the in vivo porcine brain, and histological assessment of the resulting axonal pathology. A new biomechanical model of brain injury was developed consisting of a perforated mylar surface attached to the brain and vibrated using an electromechanical shaker. Using a custom sequence with 8 interleaved wide beam emissions, brain imaging and motion tracking were performed at 2900 images/s. Shear shock waves were observed for the first time in vivo wherein the shock acceleration was measured to be 2.6 times larger than the surface acceleration ( 95g vs. 36g). Histopathology showed axonal damage in the impacted side of the brain from the brain surface, accompanied by a local shock-front acceleration of >70g. This shows that axonal injury occurs deep in the brain even though the shear excitation was at the brain surface, and the acceleration measurements support the hypothesis that shear shock waves are responsible for deep traumatic brain injuries.}, journal={JOURNAL OF BIOMECHANICS}, author={Chandrasekaran, Sandhya and Santibanez, Francisco and Long, Tyler and Nichols, Tim and Kait, Jason and Bruegge, Ruth Vorder and Bass, Cameron R. 'Dale' and Pinton, Gianmarco}, year={2024}, month={Mar} }
 @article{chandrasekaran_santibanez_tripathi_deruiter_bruegge_pinton_2022, title={In situ ultrasound imaging of shear shock waves in the porcine brain}, volume={134}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2021.110913}, abstractNote={Direct measurement of brain motion at high spatio-temporal resolutions during impacts has been a persistent challenge in brain biomechanics. Using high frame-rate ultrasound and high sensitivity motion tracking, we recently showed shear waves sent to the ex vivo porcine brain developing into shear shock waves with destructive local accelerations inside the brain, which may be a key mechanism behind deep traumatic brain injuries. Here we present the ultrasound observation of shear shock waves in the acoustically challenging environment of the in situ porcine brain during a single-shot impact with sinusoidal and haversine time profiles. The brain was impacted to generate surface amplitudes of 25-33g, and to propagate a 40-50 Hz shear waves into the brain. Simultaneously, images of the moving brain were acquired at 2193 images/s, using a custom sequence with 8 interleaved ultrasound propagation events. For a long field-of-view, wide-beam emissions were designed using time-reversal ultrasound simulations and no compounding was used to avoid motion blurring. For a 40 Hz, 25g sinusoidal impact, a shock-front acceleration of 102g was measured 7.1 mm deep inside the brain. Using a haversine pulse that models a realistic impact more closely, a shock acceleration of 113g was observed 3.0 mm inside the brain, from a 50 Hz, 33g excitation. The experimental velocity, acceleration, and strain-rate waveforms in brain for the monochromatic impact are shown to be in excellent agreement with theoretical predictions from a custom higher-order finite volume method hence demonstrating the capabilities to measure rapid brain motion despite strong acoustical reverberations from the porcine skull.}, journal={JOURNAL OF BIOMECHANICS}, author={Chandrasekaran, Sandhya and Santibanez, Francisco and Tripathi, Bharat B. and DeRuiter, Ryan and Bruegge, Ruth Vorder and Pinton, Gianmarco}, year={2022}, month={Mar} }
 @article{chandrasekaran_tripathi_espindola_pinton_2021, title={Modeling Ultrasound Propagation in the Moving Brain: Applications to Shear Shock Waves and Traumatic Brain Injury}, volume={68}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2020.3022567}, abstractNote={Traumatic brain injury (TBI) studies on the living human brain are experimentally infeasible due to ethical reasons and the elastic properties of the brain degrade rapidly postmortem. We present a simulation approach that models ultrasound propagation in the human brain, while it is moving due to the complex shear shock wave deformation from a traumatic impact. Finite difference simulations can model ultrasound propagation in complex media such as human tissue. Recently, we have shown that the fullwave finite difference approach can also be used to represent displacements that are much smaller than the grid size, such as the motion encountered in shear wave propagation from ultrasound elastography. However, this subresolution displacement model, called impedance flow, was only implemented and validated for acoustical media composed of randomly distributed scatterers. Herein, we propose a generalization of the impedance flow method that describes the continuous subresolution motion of structured acoustical maps, and in particular of acoustical maps of the human brain. It is shown that the average error in simulating subresolution displacements using impedance flow is small when compared to the acoustical wavelength ( $\lambda $ /1702). The method is then applied to acoustical maps of the human brain with a motion that is imposed by the propagation of a shear shock wave. This motion is determined numerically with a custom piecewise parabolic method that is calibrated to ex vivo observations of shear shocks in the porcine brain. Then the fullwave simulation tool is used to model transmit-receive imaging sequences based on an L7-4 imaging transducer. The simulated radio frequency data are beamformed using a conventional delay-and-sum method and a normalized cross-correlation method designed for shock wave tracking is used to determine the tissue motion. This overall process is an in silico reproduction of the experiments that were previously performed to observe shear shock waves in fresh porcine brain. It is shown that the proposed generalized impedance flow method accurately captures the shear wave motion in terms of the wave profile, shock front characteristics, odd harmonic spectrum generation, and acceleration at the shear shock front. We expect that this approach will lead to improvements in image sequence design that takes into account the aberration and multiple reflections from the brain and in the design of tracking algorithms that can more accurately capture the complex brain motion that occurs during a traumatic impact. These methods of modeling ultrasound propagation in moving media can also be applied to other displacements, such as those generated by shear wave elastography or blood flow.}, number={1}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Chandrasekaran, Sandhya and Tripathi, Bharat B. and Espindola, David and Pinton, Gianmarco F.}, year={2021}, month={Jan}, pages={201–212} }
 @article{chandrasekaran_pankow_peters_huang_2017, title={Composition and structure of porcine digital flexor tendon-bone insertion tissues}, volume={105}, ISSN={1549-3296}, url={http://dx.doi.org/10.1002/jbm.a.36162}, DOI={10.1002/jbm.a.36162}, abstractNote={Abstract}, number={11}, journal={Journal of Biomedical Materials Research Part A}, publisher={Wiley}, author={Chandrasekaran, Sandhya and Pankow, Mark and Peters, Kara and Huang, Hsiao-Ying Shadow}, year={2017}, month={Aug}, pages={3050–3058} }