Dynamic instrumented palpation (DIP)—a new method for soft tissue quality assessment; application to engineered mechanical phantom materials

Abstract

This paper presents a novel way of assessing the quality of biological tissue for diagnostic purposes, dynamic instrumented palpation. The method involves applying a controlled modulated strain or displacement to the tissue and measuring the resulting force as a function of time. The method is distinct from dynamic elastography in that the force and displacement are applied and measured by direct mechanical means at relatively low frequency (up to a few tens of Hz) and is more akin to a conventional mechanical test. The dynamic relationship between the force/stress and the strain/displacement is expressed as a function of frequency, this function being the measure to be correlated with tissue quality. The method is applied here to indentation of a set of engineered phantoms, intended to represent a controlled range of tissue quality, by altering the type and distribution of a harder and a softer phase. In the present work, the phantom tissues were engineered from natural and synthetic sponges impregnated with either silicone or gelatin, although the ultimate application is to human prostate, which can be considered as a biphasic structure (at least at the macro-scale), to distinguish between benign prostate disease and cancer. The work demonstrates that a range of frequencies can be used to yield a characteristic for the material which depends not only on the material type(s) but also on the morphology of the constituents. The method, therefore, shows good promise for application to the identification of multicomponent soft tissue make-up. As such, it is complementary to dynamic elastography, and its value lies in it being deployable in vivo as an adjunct during minimally invasive interventions. Future work will be aimed at establishing the capability of the method on human prostate tissue both in vitro and in vivo.