Minimally invasive instrument for in vivo measurement of solid organ mechanical impedance

The medical field, and surgeons in particular, are turning to engineers to develop systems that help them learn their craft better. Mannequin-based systems, animal labs and surgery on cadavers each have drawbacks that could be addressed through realistic computer-based surgical simulation systems. To generate a simulation that includes both tactile/haptic and visual feedback, one must know what the material properties of tissue are, so that a finite element or other model can generate the proper predictions for interactions between surgical instruments and tissue. This thesis presents the design, construction, characterization, and use of a minimally invasive surgical instrument designed to measure the linear visco-elastic properties of solid organs. The Tissue Material Property Sampling Tool, or TeMPeST 1-D, applies a small amplitude vibration normal to the surface of an organ such as liver or spleen, and records the applied force and displacement. It has a range of motion of up to 1mm, and can apply up to 300mN force with a 5mm right circular indenter. The open loop bandwidth of the system is approximately 100Hz, which is greater than the bandwidth of both the human visual and motor control systems. The relationships between indentation force and displacement and material properties such as the elastic modulus of tissue are presented, and models are developed that show the expected response to a standard tissue model. Characterization and calibration tests demonstrate the response of the prototype components. Experiments performed on spring and mass elements and on silicone gel samples, which mimic tissue response, show that the TeMPeST 1-D can accurately measure their force-displacement responses. The TeMPeST 1-D and its data acquisition system are intended to be portable, to be easily transported to and used in an operating room. The system was used in proof-of-concept experiments performed on live pigs; an example of the measured properties of porcine liver is presented. The TeMPeST 1-D is the first in a series of instruments that will be developed to support the generation of a comprehensive atlas of tissue material properties. Thesis Supervisor: Dr. J. Kenneth Salisbury Title: Principal Research Scientist, Mechanical Engineering, MIT Professor, Departments of Computer Science and Surgery, Stanford Thesis Committee: Dr. J. Kenneth Salisbury, Chairperson Principal Research Scientist, Mechanical Engineering, MIT Professor, Departments of Computer Science and Surgery, Stanford Dr. Mandayam A. Srinivasan Principal Research Scientist, Department of Mechanical Engineering, MIT Dr. David L. Trumper Associate Professor of Mechanical Engineering, MIT Acknowledgments This work was supported in part by: the Center for Innovative Minimally Invasive Therapy (CIMIT) at Massachusetts General Hospital (MGH), with funding from the Department of the Army, under contract number DAMD12-99-2-9001. The views and opinions expressed do not necessarily reflect the position or the policy of the government, and no official endorsement should be inferred; a National Science and Engineering Research Council (NSERC) of Canada PGS-B scholarship. There are probably more people than I can say who have helped me to complete this work and keep me on track. In particular, I'd like to thank: my committee members, Prof. Ken Salisbury, Dr. Mandayam Srinivasan and Prof. Dave Trumper, for their support, advice, and good ideas, and especially for helping to define a realistic scope for this research; Dr. Karen Moodie, Prof. Joe Rosen and Dr. William Laycock of Dartmouth Medical School and Onux Medical, Inc. for their assistance in gaining access to the Dartmouth Animal Resources Center pigs; and Karen again (especially for help with the paperwork), Greg Burke and Sam Weinstein for taking care of the pigs while my data was being acquired; Joe Samosky (for being amazed with the work) and Rachel Oppenheimer of Dr. Martha Gray's cartilage biomechanics and imaging laboratory at the Harvard Institutes of Medicine, for assistance in measuring the properties of my standard materials; Dr. Robert Howe of Harvard University and Dr. Parris Wellman for the idea for and data on the silicone gel that I used as a prelude to real tissue; Professors Chris Scott and Anne Mayes, and You-Yeon Won, of the Department of Material Science and Engineering, for providing access to their materials testing apparatus and help in measuring the properties of the standard gels; Dr. David Schloerb for assistance with the MIT Laboratory for Human and Machine Haptics tactile stimulator. Dr. Steven Dawson and Dr. Stephane Cotin of the Simulation Group of CIMIT at MGH for their support and interest throughout the research, and CIMIT for the funding that supported it; Ela, Jesse, Arrin, Andrew and Brian and the other Haptics Lab members who've passed through and made the stay more enjoyable movie night anyone? Ron Wiken of the Artificial Intelligence Lab, for advice, assistance, and keeping the shop facilities in such great shape it's been a joy to build stuff here; all of the other people whose paths I've crossed and have helped me get just that much farther; and last, but certainly not least, my parents, Peter and Erika, my sisters, Susan and Andrea, and my girlfriend, Rene, who have seen me through the last four and a half years with love and understanding I'm finally done! "0 frabjous day! Callooh! Callay! " He chortled in his joy. Lewis Carroll, Jabberwocky