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Steven L Dawson

Publications and source records attributed to Steven L Dawson.

3 recordsLinked to original sources
PubMed2003

Truth cube: establishing physical standards for soft tissue simulation.

Accurate real-time models of soft tissue behavior are key elements in medical simulation systems. The need for fast computation in these simulations, however, often requires simplifications that limit deformation accuracy. Validation of these simplified models remains a challenge. Currently, real-time modeling is at best validated against finite element models that have their own intrinsic limitations. This study develops a physical standard to validate real-time soft tissue deformation models. We took CT images of a cube of silicone rubber with a pattern of embedded Teflon spheres that underwent uniaxial compression and spherical indentation tests. The known material properties, geometry and controlled boundary conditions resulted in a complete set of volumetric displacement data. The results were compared to a finite element model analysis of identical situations. This work has served as a proof of concept for a robust physical standard for use in validating soft tissue models. A web site has been created to provide access to our database: http://biorobotics.harvard.edu/truthcube/ (soon to be http://www.truthcube.org).

Animals↗
PubMed2003

Independent testing of soft tissue visco-elasticity using indentation and rotary shear deformations.

Numerous techniques exist to measure the mechanical properties of soft tissues in vivo, such as mechanical stretching, indentation or shearing, as well as elastographic methods employing ultrasound or other imaging modes. Many groups have reported properties which do not necessarily correspond with each other due to differences in choice of technique, tissue model or other variations. This work deliberately makes use of the two independent modes of indentation and rotary shear, on the same material samples, employing similar modeling approximations, to attempt to determine the common, underlying material properties. This paper introduces the ROSA-2 rotary shear instrument, and presents its mechanical characteristics, as well as presenting validation experiments that were performed to verify non-slip contact with tissue. Measurements made with it are compared with those acquired with the TeMPeST l-D indentation instrument. Initial testing showed reasonably agreement when testing silicone gel samples, over a restricted range of frequencies. When testing bovine liver samples in vitro and porcine liver in vivo, significant discrepancies were found. The potential sources of these differences will be discussed, as will directions for ongoing work.

Animals↗