Measuring the elastic modulus of<i>ex vivo</i>small tissue samples

TLDR

Elastography methods have been proposed to image tissue elasticity, yet a fundamental understanding of tissue properties required to interpret these images remains lacking. The study aims to develop a system for measuring the Young's modulus of small soft tissue specimens. The system accommodates irregularly shaped samples and measures modulus by indenting an unconfined block while recording force, and also by applying quasi‑static magnetic resonance elastography to reconstruct modulus from displacement data. Finite element analysis demonstrates that the force–displacement slope can be converted to Young's modulus via a geometry‑dependent factor, and preliminary measurements on breast tissues confirm the method’s feasibility.

Abstract

Over the past decade, several methods have been proposed to image tissue elasticity based on imaging methods collectively called elastography. While progress in developing these systems has been rapid, the basic understanding of tissue properties to interpret elastography images is generally lacking. To address this limitation, we developed a system to measure the Young's modulus of small soft tissue specimens. This system was designed to accommodate biological soft tissue constraints such as sample size, geometry imperfection and heterogeneity. The measurement technique consists of indenting an unconfined small block of tissue while measuring the resulting force. We show that the measured force–displacement slope of such a geometry can be transformed to the tissue Young's modulus via a conversion factor related to the sample's geometry and boundary conditions using finite element analysis. We also demonstrate another measurement technique for tissue elasticity based on quasi-static magnetic resonance elastography in which a tissue specimen encased in a gelatine–agarose block undergoes cyclical compression with resulting displacements measured using a phase contrast MRI technique. The tissue Young's modulus is then reconstructed from the measured displacements using an inversion technique. Finally, preliminary elasticity measurement results of various breast tissues are presented and discussed.