| dc.description.abstract | Since the first successful liver transplant in 1968 the surgery has become very common and 6,291 patients received liver transplants in 2010 in the United States. However, the monitoring methods used post-surgery, in the recovery phase, are still very basic and rely mainly on blood tests and looking for unusual symptoms. Complications are usually detected after the organ is substantially damaged which poses a risk to the patients’ life. This dissertation presents the development and testing of an implantable sensor that can potentially be used to monitor the transplant continuously and transmit the information wirelessly to the medical staff for timely intervention. Such a sensor could have a great effect on survival and reduction of retransplantation rates.
The presented sensor employs near infrared spectroscopy to measure perfusion changes, arterial oxygenation and venous oxygenation in the parenchyma of the liver tissue and the supplying vessels. Light at three different wavelengths (735-, 805- and 940-nm) is shined on the tissue and the diffuse reflectance is collected via a photodetector. The collected signals can be transmitted wirelessly to an external unit for processing and display. In this dissertation, different perfusion and oxygenation monitoring techniques are reviewed and the instrumentation of an NIRS based wireless sensor is introduced. A phantom that mimics the anatomy of the liver and its optical and mechanical properties is presented. The processing methods to extract the information of interest from the diffuse reflectance are described in details. Finally, results from in vitro phantom experiments, ex vivo perfused livers and in vivo porcine studies are presented.
The first in vivo wireless monitoring of hepatic perfusion and oxygenation levels is reported. The studies show that the sensor can track perfusion changes with a resolution of 0.1 mL/min/g of tissue. The possibility of tracking oxygen saturation changes is also shown as well as the ability to separate them from perfusion changes. Combining results from the pulsatile wave and DC levels, venous and arterial oxygen saturation changes were tracked with a resolution of 1.39% and 2.19% respectively. In conclusion, optical spectroscopy is shown to track perfusion, and arterial and venous oxygenation in tissue. In particular, the method was tested on hepatic and intestinal tissue. | en |
