Design and Validation of Computational Blood Clot Elastometry Model for Use with Magnetomotive Ultrasound

The size and stiffness of blood clots are medically important quantities for making treatment decisions, and although ultrasound can approximate the compressive stiffness of clots as a proxy for clot age, current ultrasound-based imaging methods lack quantitative clot stiffness measurements. Magnetomotive ultrasound (MMUS), an emerging imaging technique that uses magnetic nanoparticles as a contrast agent by driving them with a sinusoidal magnetic force, has the potential to provide quantitative results for size and stiffness, and hence may be valuable for making treatment decisions. We designed a computational elastometry model of a blood clot via finite element analysis (FEA) that relates the resonance frequency of a clot to its stiffness. We determined experimentally feasible and clinically relevant geometries, and found the maximum magnetic driving frequency required for future MMUS blood clot imaging devices. To validate our model, we designed two semi-ellipsoidal blood clot-mimicking phantoms by setting gelatin in dome-shaped molds and quantitatively measured Young's modulus using resonant acoustic spectroscopy. Our experimental and computational FEA results agree with under 11% error and were sufficiently precise to allow for differentiation among stiffnesses. A future MMUS system would need a driving frequency of at least 72.5Hz to measure clots as small as 0.5mL. Our FEA model is a promising tool for stiffness prediction of semi-ellipsoidal model blood clots.