Sensitivity improvement of a nuclear magnetic resonance method to monitor a bioartificial pancreas

Non-invasive monitoring of implanted devices is becoming key in developing tissue-engineered structures intended to provide alternative or complementary treatment to people with organ or tissue impairment and/or loss. Bioartificial pancreases for the treatment of Type I diabetes are an example of such structures under development. Nuclear magnetic resonance (NMR) imaging and spectroscopy have already shown their potential for monitoring of these pancreatic substitutes and detecting their early marker of failure. However, the sensitivity of these NMR methods was limited. The studies presented in this dissertation investigate sensitivity improvement by developing inductively-coupled implantable RF coil systems at high magnetic field strength not only for 1H detection, but also for the detection of other informative, but less sensitive nuclei, such as 19F and 31P. An inductively-coupled implantable coil system was first developed for 1H detection to demonstrate the use on inductively-coupled implantable coil system at 11.1 T. Secondly, a development of a receive-only inductively-coupled implanted coil system was investigated to further improve 1H detection and increase localized spectroscopy performance. The feasibility of double frequency inductively-coupled implantable coil systems for simultaneous detection of 1H-31P and 1H- 19F were explored next, toward the development of a multiple frequency system. The requirements of these coil systems for a complete monitoring of a bioartificial construct were discussed. In parallel to the coil system developments, the inclusion of an RF coil within the implanted pancreatic construct was also studied to address the restrictions it imposed on the construct design. The results for 1H detection establish that large gains in signal-to-noise can be obtained with the use of inductively-coupled implanted coil systems when compared to the use of standard surface coils. This improvement provides a means to better analyze the structures of implanted bioartificial constructs and their changes over time on NMR images. It can also lower the limit of detection when spectroscopy is performed to detect choline NMR signal and allow for better quantitative analysis of bioartificial organ functions. A receive-only inductively-coupled implanted coil system was also successfully developed to further enhance localized spectroscopy since a more homogeneous NMR excitation magnetic field could be achieved with its use compared to the use of a transmit-receive system. 31P and 19F spectroscopy was also performed using single-frequency inductively-coupled implanted coil system for 31P detection to detect adenosinetriphosphate (ATP) and for 19F detection to detect perfluorocarbons (PFC). These results set the standards for the development of double-frequency inductively-coupled implantable coil systems. The feasibility of double-frequency inductively-coupled implantable coil system was assessed as well. Furthermore, data shows that a coil-construct assembly allowed insulin-producing cells to function and stay viable for extended periods of time in vitro. The return to normoglycemia in diabetic mice after coil-construct assembly implantation was also demonstrated while enhanced non-invasive monitoring of the implanted constructs was made possible using NMR methods.