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UW-Madison BME 300 - Cooling Device for Transesophageal Ultrasound

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1"" Cooling Device for Transesophageal Ultrasound Advisor: John Webster Client: Tim Hacker Team Members: Team Leader- Mike Conrardy BWIG- Andrew Bertram BSAC- David Leinweber Communicator- Joel Webb Date: May 5, 20102"" Abstract. The purpose of this design was to create a cooling device for a Philips X7-2T 3D transesophageal ultrasound probe. The device should be small enough to fit into the esophagus of a swine model when attached to the probe, and should keep the internal probe temperature at a steady state value below 42 degrees Celsius. A prototype of this device was fabricated using vinyl tubing, low-density polyethylene (LDPE) and Tygon tubing, and was tested both in vitro and in vivo. The prototype successfully held the internal probe temperature below 42 degrees Celsius in each test and kept the temperature at a steady state value during in vitro testing. However, the size of the device was larger than specified when an additional EM tracking device was attached to the probe tip, and it was difficult to obtain a completely watertight seal on our prototype.3""Table of Contents Abstract Table of Contents Problem Statement Background Heart Disease Ultrasound Imaging Design Specifications Design Alternatives Liquid Tubing Gas Cooling Liquid Reservoir Design Decision Final Design Revised Design Construction of Revised Design Final Design Construction Testing Future Work References Appendix A: Product Design Specifications Appendix B: Testing Data Page 2 3 4 4 4 6 7 8 8 9 10 10 12 12 13 13 15 19 21 22 254"" Problem Statement Our client has been using a prototype of a new 3-D transesophageal ultrasound probe in pigs to image an injection catheter in the left ventricle. The injection catheter and imaging method are being tested as a method to deliver stem cells to damaged heart tissue. The continuous imaging that is required to determine the placement of the injection catheter and the stem cells causes the probe to overheat and turn off until it has cooled down enough to prevent any tissue damage. Our client would like a device to cool the ultrasound probe so that he could image for a longer period of time without tissue damage. This project would have commercial potential, as this is a novel use of 3-D ultrasound. The cooling device could be as simple as using cold saline to flush the probe to a more sophisticated electronic cooling device. Background Heart Disease Tim Hacker and Amish Raval of the UW Department of Medicine are conducting research to determine to what extent stem cells can regenerate dead heart tissue. The American Heart Association reports that there are 1,260,000 new and recurrent coronary attacks occur per year. About 37% of people who experience a coronary attack in a given year die from it (Heart Attack and Angina Statistics). Additionally, an estimated 5.7 million Americans live with heart failure with 670,000 new cases diagnosed each year (Heart Attack and Angina Statistics). By creating a method where tissue in the heart could be regenerated, many of these cases could be better treated. A heart attack occurs when blood flow is blocked and the myocardial tissue gets starved of blood. Without oxygen from the blood, myocardial cells die and the muscle tissue can become permanently damaged without treatment. The goal of this research is to discover if direct injection of mesenchymal stem cells isolated from bone marrow can be effectively injected into5""dead heart tissue, and if so, how these cells could be used to treat cardiovascular disease. Mesenchymal bone marrow cells are able to differentiate into myocardial cells and show great promise for heart tissue regeneration (Wu). Hope is that this treatment will be able to regenerate dead heart tissue caused by heart attacks in a minimally invasive manner. For a typical procedure, our client begins by inducing heart attacks in swine models, which creates regions of dead tissue in the heart. He then enters the left ventricle of the heart with a single injection catheter via the femoral artery. The current catheter used is the Myostar made by Biosense-Webster (see figure 1). This catheter incorporates a retractable needle tip and exhibits a single degree of freedom. Figure 1: The Myostar injection catheter made by Biosense Webster currently being used by the client (Callans et al). During this process he utilizes ultrasound imaging to determine the location of the catheter in the heart. He then determines his location based on ultrasound and injects the stem cells into the region of cell death. However, each procedure using the Myostar catheter is very time consuming, and the area of dead myocardial tissue is often large which requires numerous6""injections. In addition, the Myostar catheter must be repositioned for each injection, which is extremely difficult. With only one degree of freedom, it is hard for our client to position the tip of the catheter accurately, and during the procedure the heart remains beating, which adds to the difficulty. Due to the long duration of the procedure, our client has experienced problems while obtaining continuous images because, due to a safety mechanism, the ultrasound machine shuts off when the internal probe temperature reaches 42.5 degrees Celsius. To solve this problem, our client has created a simple device that consists of a catheter that is attached to the ultrasound probe by surgical tape that drips cold saline onto the tip of the ultrasound probe. The cold saline cools the ultrasound device to keep it at a steady state temperature. The device is an open loop system, thus, the saline drips off the ultrasound probe and into the swine’s stomach. Our client looks for a device that can be to attached to the end of the probe and cool the device so he is able to image for extended periods of time without the ultrasound machine turning off. Ultrasound Imaging During the procedure performed by out client, 3D transesophageal ultrasound imaging is utilized to determine the location of injections. For this imaging, our client uses a Philips X7-2T ultrasound probe, shown in Figure 2. Transesophageal ultrasound imaging utilizes an ultrasound transducer placed on an endoscope. The endoscope can be inserted through the mouth and into the esophagus, and in this location the ultrasound transducer will produce high frequency sound waves that reflect off the tissue to be recorded to produce images of the heart that are called


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UW-Madison BME 300 - Cooling Device for Transesophageal Ultrasound

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