Optical Detuning Strategies for Shielded Loop Resonators

PURPOSE: To compare detuning performance and evaluate power requirements of optical detuning methods and to demonstrate feasibility of an optically-detuned 4-channel receive array. METHODS: Four optical detuning methods were compared in simulations, bench tests, and phantom measurements at 3T against conventional galvanic detuning. Passive detuning was also tested as an additional wireless detuning option. Optical power requirements for the detuning networks were investigated, and a flexible optically-detuned 4-channel shielded loop resonator (SLR) array was constructed and tested in vivo. RESULTS: A photodiode-PIN diode combination exhibited the highest unloaded Q (68.6) and Q ratio (1.9), with detuning performance and signal-to-noise ratio comparable to that of galvanic detuning at an optical power of 10 mW. Using this detuning strategy, in vivo images of the knee and brain were successfully acquired with a 4-channel flexible array. CONCLUSION: Optical detuning is a practical alternative to conventional galvanic detuning in flexible SLR arrays. With developments in optical signal and power transmission, optimizing optical detuning while meeting manageable power requirements is an important step toward fully optical receive coil arrays. This study provides a reference point for the total optical power required for active detuning in such optical coil systems.