Multiple frequency MR implantable coil system for \textit{in vivo} studies of bioartificial pancreas at 11.1 T

Bioartificial pancreatic macroconstructs may deliver insulin secreting cells for blood glucose regulation. Non-invasively monitoring \textit{in vivo} is key to understanding its function and efficacy. Initial NMR imaging {\&} spectroscopy showed great promise with surface coils at 4.7 T. Sensitivity limitations restrict measurements so we developed an inductively-coupled multiple-frequency coil system for 11.1 T. This system contains an implantable loop-gap resonator, inductively coupled to an external coil, resonating at 471 MHz for $^{1}$H and optimized for $^{31}$P at 191 MHz. This system has a sensitivity gain of $\sim $5.2 ($\pm $2.3) over a surface coil. Images were acquired for both frequencies. Ongoing work focuses on: 1) a receive-only coil system, 2) adding a third resonance (443 MHz for $^{19}$F), and 3) developing coating material and embedding the implantable coil in the macroconstruct. This system will be characterized in vitro prior to its use in vivo.