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Objective To model inductive coupling of endovascular coils with transmit RF excitation for selecting coils for MRI-guided interventions. Methods Independent and computationally efficient FEM models are developed for the endovascular coil, cable, transmit excitation and imaging domain. Electromagnetic and circuit solvers are coupled to simulate net B1+ fields and induced currents and voltages. Our models are validated using the Bloch Siegert B1+ mapping sequence for a series-tuned multimode coil, capable of tracking, wireless visualization and high resolution endovascular imaging. Results Validation shows good agreement at 24, 28 and 34 μT background RF excitation within experimental limitations. Quantitative coil performance metrics agree with simulation. A parametric study demonstrates trade off in coil performance metrics when varying number of coil turns. Tracking, imaging and wireless marker multimode coil features and their integration is demonstrated in a pig study. Conclusion Developed models for the multimode coil were successfully validated. Modeling for geometric optimization and coil selection serves as a precursor to time-consuming and expensive experiments. Specific applications demonstrated include parametric optimization, coil selection for a cardiac intervention and an animal imaging experiment. Significance Our modular, adaptable and computationally efficient modeling approach enables rapid comparison, selection and optimization of inductively-coupled coils for MRI-guided interventions.

Wireless links with implantable devices can help in real-time monitoring of symptoms, irregularities, implanted device efficacy and their reconfiguration. We present the design of a low-power wideband voltage controlled oscillator (VCO) to facilitate implantable wireless telemetry. A coupled SAW-LC resonator design combines high Q and spectral purity of a SAW element and tunability of an LC-tank. The designed 2.7 MHz bandwidth VCO is suitable for full duplex communication protocols in the MedRadio band with frequency agility and higher duty cycles, in conformance with FCC regulations. Output power at the fundamental frequency is above -7.5 dBm for a wide range of load impedances. Output power load insensitivity provides a wide margin for selection of communication system parameters, variability in device placement, temporal variation in tissue properties and flexibility for implants at different locations (e.g. heart, gastrointestinal tract, brain). The maximum output power variation in the entire 2.7 MHz band is limited to 1.3 dBm. Sensitivity of oscillation frequency to loading can be addressed by individual device calibration. The small size, component count and low DC power consumption (1.9 V, ~1.95 mW) is favorable for including in a miniaturized and integrated design assembly with a battery-powered implanted device.

We demonstrate a method, independent of coil geometry, orientation and separation, to measure inductive wireless power transfer to an implanted coil, without a bidirectional communication link. Load switching on the implantable coil at 1 kHz modulates the 13.56 MHz carrier signal. A lock-in amplifier detects current perturbation in the excitation coil at the switching frequency producing an output proportional to the induced current in the implantable coil. Measurements show good agreement with analytical values at different locations in a 5mm x 5mm grid for parallel and orthogonal coil orientations. Observed standard deviations are within 10% and 15% for parallel and orthogonal orientations.