Phantom Simulation of Liver Motion During Normal Breathing

1. Phantom Simulation of Liver Motion During Normal Breathing Ian Dallemeyer1, Tuta Guerra1, Ian Henderlong1 Advisor: Dr. Robert Galloway1 1 Department of Biomedical Engineering, Vanderbilt University Nashville, TN Results/Testing Abstract Image-guided liver surgery is a minimally invasive therapy to treat primary and metastatic liver cancer with little damage to healthy tissue. This design project focuses on creating a phantom simulation of liver motion during normal breathing in order to provide an accurate, reusable device to practice and perfect image guided-liver surgery techniques. This model consists of two different components; a cart design with base and vehicle that support the silicon phantom liver and a circuit design which produces the cyclic power output. Muscle Wire, which contracts and relaxes when heated, connects the two components and creates the simulated liver motion during normal breathing. The model successfully generates comparable displacement and frequency, with minimal difference in regard to motion of an actual human liver. Design Specifications -1-D Linear Motion (cranial – caudal direction) -10.8 + 2.5 mm (Average Total Liver Motion) - Breath Frequency ~= .11 Hz (1 breath/9sec) - Measurements made with Optotrak 3220 Introduction The American Cancer Society estimates 15,420 people will die of liver cancer in the U.S. during 2005. This cancer is about 10 times more common in developing counties in East Asia, Africa, and Asia than in the U.S and in many of these countries it is the most common type of cancer. With the length of wire used (30 cm), the average displacement of the phantom was 10.43 + 0.535 mm. Over an 8-9 second interval, our phantom moved ~10 mm in about half the cycle time or 4-5 seconds, and returned to rest in about the same amount of time. A plot of the cart motion vs. displacement is shown above. A plot of the cart motion vs. displacement is shown above and is very comparable to the ATLM data recorded by Optotrak 3220. Current therapies for liver cancer are incredibly invasive. Often cancer is large, is found in many different parts of the liver, or has spread beyond the liver so complete removal of most liver cancers is not possible. Image-guided liver surgery offers the possibility of a more effective therapy with less side effects. Image guided surgery uses tomographic imaging techniques such as CT, MR, and PET to create a registered image that define the spatial extent, location and structure of the diseased area and the Methods and Materials Cart Design - Plywood for base, cart, track - Oak for spring recoil system - 22 3/8” zinc screws - 4 1” hooks -2 extension springs k ~= 9 x 10^6 N/m - 4 1” diameter plastic wheels Circuit Design Conclusion/Future Work The ATLM and frequency is accurately reproduced by the phantom model. The waveform of the documented human liver motion is slightly different than the results produced by our phantom model. The most important function of the phantom model is the movement of the liver being accurate with the measured average total liver motion. The measurements made in the body show an enormous amount of error, nearly 20% variance of the average total liver motion. The muscle wire used does not produce that type of error and therefore cannot accurately simulate the wide range of variance to the millimeter necessary for the simulation. Therefore, a different type of linear actuator may be more sufficient to reproduce the variance needed in simulating liver motion due to breathing. Materials used would be the area that could most drastically effect the accuracy and precision of this model. This being the first prototype for a phantom liver model, many of the materials are crude and are designed for use on a much larger scale, in particular the wheels used on the cart. Also of note, the order in which parts are assembled has an effect on the precision of movement, particularly in the track system. References: - Herline AJ, Stefansic JD, Debelak JP, Hartmann SL, Wright Pinson C, Galloway RL, Chapman WC. Image Guided Surgery: Preliminary; Feasibility Studies of Frameless Stereotactic Liver Surgery. June 1999 Archives of Surgery 134:644-650 - Korin HW, Ehman RL, Riedere SJ, Felmlee JP, Grimm RC.Respiratory kinematics of the upper abdominal organs: A quantitative study. Magnetic Resonance Medicine 1992;23:172 - Nawaratne, Sumith; Fabiny, Robert; Brien, Joanne E.; Zalcberg, John; Cosolo, Walter; Whan, Andrew; Morgan, Denis J. Accuracy of Volume Measurement Using Helical CT. Journal of Computer Assisted Tomography. 21(3):481-486, May/June 1997. - Sarfaraz M, Wu X, Lodge MA, Yu CX. Automatic CT-SPECT registration of livers treated with radioactive microspeheres. Physics in Medicine and Biology. Vol 49, May 4, 2004. location, function and topology of the normal anatomy about the disease areas. Using these images as maps, surgeons can effectively guide the delivery of therapy in space and time to localized regions of the liver. These therapies include radio-frequency ablation, chemoembolization, and other localized minimally invasive therapies. Currently, porcine livers, whose structure most closely resembles that of humans, are used to simulate liver surgery. However, the cost and incompatibility to humans in terms of structure and motion render this model insufficient in providing an accurate and affordable simulator. Therefore, it is necessary to develop a phantom simulation of liver motion during normal breathing using an anatomically correct phantom. Market Potential -ACS estimates 17,550 new cases of primary liver cancer in U.S. 200,000 new cases of metastatic liver -International Market: 250,000 cases in China; most frequent cancer in developing countries of East Asia, Africa and Asia -Estimated market for IGLS is 10x greater than current IGNS market -IGLS Market : $3.0-7.5 billion -Porcine Liver costs $1,000-2,000. Phantom model $150-$200 Muscle Wire - Flexinol 150 LT - Nitinol Shape Memory Alloy - Resistance = 50Ω/m - Diameter = 150 μm - Activation Current = 400mA