Standoff tracking of medical interventional devices using non-contact microwave thermoacoustic detection

Tracking of medical interventional devices is performed using non-contact microwave-induced thermoacoustic detection. The interventional device is modeled with an exposed tip coaxial probe in an agar phantom and it uses the inherent microwave excitation to generate modulated thermoacoustic signals. The resulting ultrasound signal is detected by custom designed capacitive micromachined ultrasonic transducers (CMUTs) at a standoff and without any contact with the target. The dependency of the specific absorption rate (SAR) profile on the excitation frequency and probe tip length is examined in order to determine optimal operating conditions for resolution and signal level. An excitation frequency of 2.35 GHz is chosen and is amplitude-modulated with a 72 kHz pulse train to match the center frequency of the CMUTs. A two transducer system is employed to achieve cm-scale resolution via 2-dimensional location tracking using a modified trilateration technique.