Magnetic Resonance Elastography (MRE), a non-invasive imaging technique that maps tissue stiffness using magnetic fields, Radio frequency coils, and low frequency vibrations, has become a key tool in brain biomechanics, but its broader use is limited by the lack of validated brain-mimicking phantoms. Prior studies have shown that MRE can yield shear moduli consistent with dynamic shear testing and indentation in soft gelatin phantoms, and in vivo brain MRE has established gray, and white-matter shear stiffness on the order of 1–3 kPa at typical vibration frequencies (∼60 Hz). Despite this progress, there is still no widely adopted material system specifically tuned to replicate the viscoelastic properties of living brain tissue for use in injury simulation or neuromodulation testing, where brain-like stiffness and damping must be achieved at clinically relevant frequencies. In this study, a polyvinyl alcohol (PVA)/phytagel (PHY) hydrogel phantom was developed to mimic the viscoelastic behavior of brain tissue and validated using both rheometry and MRE. A composite hydrogel was synthesized from PVA and PHY using controlled freeze-thaw cycles to tune viscoelastic behavior. Samples were molded into cylindrical shapes to match the 6-in. liver MRE transducer available at the Veterans Affairs Hospital. Petri dish samples from each batch were first tested using a rheometer to measure storage (G′) and loss (G″) moduli, yielding G′ ≈ 1.85 kPa and G″ ≈ 0.253 kPa, meaning the complex shear modulus |G*| ≈ 1.86 kPa, consistent with reported gray matter values. The same formulations were then tested using MRE to generate spatial stiffness maps. For the original bulk formulation (6% PVA, 0.85% PHY), MRE measured an average |G*| of 18.64 kPa, notably higher than both typical brain values and a commercial liver phantom measured at 3.26 kPa under identical conditions; these results motivated subsequent fine-tuning by reducing polymer concentrations to approach physiologic stiffness. Two more MRE phantom concentrations of 3% PVA, 0.43% PHY, and 1.5% PVA, 0.21% PHY, show |G*| of 7.7 and 2.1 kPa respectively. MRE of the larger cylindrical samples also revealed internal stiffness gradients and surface artifacts, offering insights not possible with mechanical testing alone and suggesting crosslinking heterogeneity at bulk scale. By expanding on gelatin-based phantom research with a brain-mimicking PVA-PHY hydrogel phantom tested at TBI-relevant frequencies, this work establishes a foundation for mechanically validated brain phantoms for traumatic brain injury research, imaging system calibration, and neuromodulation studies.
Lohr et al. (Sun,) studied this question.