Mark Ottensmeyer

Lead Investigator, Simulation Group, CIMIT, MGH

"In vivo linear elastic property measurement of porcine liver"

Surgical simulation, whether for training or for instrument or procedure prototyping, depends in part on knowledge of the material properties of the tissues in question.  Generally speaking, tissue force-displacement responses exhibit non-linearity, anisotropy, inhomogeneity and time dependent features, some or all of which may be important to include in a tissue model.  Further, tissue properties tend to change after death, so measurements made on living tissues are preferable to those made on excised samples.  A number of devices have recently been developed to measure some of these properties for solid
organ tissues in vivo, one of which is the TeMPeST 1-D. The Tissue Material Property Sampling Tool 1-D is a minimally invasive surgical instrument which exerts small normal loads on tissues and simultaneously measures displacement and applied load.  It is capable of generating vibratory stimuli up to approximately 80Hz, and has a range of motion of +/- 500um.  Through careful selection of mean applied load, and frequency and location of stimulation, it can be used to investigate linear stiffness, non-linear effects, damping/viscous characteristics and inhomogeneity over the surface of an organ such as liver or spleen.

In my talk I'll introduce the TeMPesT 1-D system.  I will discuss the geometric and other approximations, and modeling necessary for tissue parameter extraction.  I'll go into some detail on the instrument hardware and describe experiments designed to verify the performance of the instrument on known elements and materials. The talk will conclude with discussion about in vivo testing on porcine liver and spleen, currently underway.  I'll present the results of preliminary analysis of early experiments, and discuss some of the directions towards which our research is headed.