Researcher: Samuel Morais
Colaborator: Dr. Muralidhar Padala
The biomechanical properties of a tissue provide valuable insight into its functional state. For instance, assessment of the shear modulus of the myocardium can assist in timely diagnosis of conditions such as heart failure and enable customized patient-specific therapies. Notably, many relevant procedures, such as direct intramyocardial injection of gene therapy for heart failure, utilizes catheter devices to access the heart, presenting an opportunity to incorporate additional functional capabilities. Ultrasound-based shear wave elasticity imaging (SWEI) is an established non-invasive method to measure elasticity of soft tissues, yet SWEI of the heart is challenging due to limited access to the organ and tissue motion. To address these challenges, we propose the application of transient elastography (TE) using a miniaturized mechanical actuator for longitudinal shear wave (LSW) generation. A miniaturized TE system that can be integrated into a catheter device, enables real-time intracardiac measurement of myocardial elasticity during procedures where catheterization is already indicated, providing a seamless extension to current clinical workflows.
We explored the feasibility of catheter-based TE using a 2 mm x 2 mm piezoelectric actuator to excite LSWs and an array transducer to track their propagation. This approach was tested in three different tissue-mimicking phantoms with varying elastic properties and in ex vivo porcine heart tissue under fresh and preserved conditions. Spatial-temporal maps of displacement along the longitudinal direction were generated, and the shear waves speeds were estimated from the slope of peak local displacement over time. The TE-measured values were compared with those obtained using the conventional acoustic radiation force-based method for validation.
The generation of LSWs with the miniature piezoelectric actuator was demonstrated. The shear moduli values obtained from both TE and SWEI were compared across the three different phantoms, showing good agreement between these measurements (error < 8%). For the same sample, the TE-measured shear moduli were slightly lower than those measured by SWEI (for the softer phantom, 12.0 ± 1.0 kPa versus 13.1 ± 1.7 kPa, for TE and SWEI, respectively), possibly due to the different sources of shear wave excitation in each method. A similar comparison was conducted on porcine heart tissue in different conditions (fresh and fixed), revealing the increase in tissue stiffness from 84.8 ± 3.2 kPa to 276.7 ± 20.8 kPa due to preservation.
This proof-of-concept work suggests the potential use of a miniaturized piezoelectric actuator for quantitative analysis of myocardial elastic properties using TE. Assembling the small actuator with a single-element transducer for LSW tracking could enable a TE-based catheter device to access the heart via a peripheral artery, allowing intracardiac estimation of shear moduli at multiple locations along the left ventricular chamber. This approach would provide additional functionality and guidance during standard catheter-based cardiac clinical procedures.