Quantifying the Transmit-Power Threshold for Reliable Passive Detuning of Inductively Coupled Wireless Resonators in MRI: A Phantom Study.

This work develops and validates a practical method for quantifying the transmit-power threshold at which passive detuning of inductively coupled wireless resonators becomes reliable in MRI. All experiments were performed using phantoms. A near/far spatial signal ratio is computed from a series of gradient-echo (GRE) images acquired at different nominal flip angles. This ratio reveals ineffective detuning as a characteristic L-shaped curve whose inflection point marks the detuning threshold. The method was validated experimentally with wireless resonators incorporating different numbers of crossed diode pairs, at multiple static field strengths (3 and 7T), and with different scanner vendors. At 3T, the method produced consistent B 1 + thresholds across Philips and GE scanners despite their different flip-angle thresholds. The proposed method provides a practical, straightforward tool for acceptance testing and quality assurance of wireless resonator safety in both clinical and research MRI settings.