Multiaccess in vivo biotelemetry using sonomicrometry and M-scan ultrasound imaging

Objective: In this paper, we investigate the use of commercial off-the-shelf diagnostic ultrasound readers to achieve multiaccess wireless in vivo telemetry with millimeter-sized sonomicrometry crystal transducers. Methods: The sonomicrometry crystals generate ultrasonic pulses that supersede the echoes generated at the tissue interfaces in response to M-scan interrogation pulses. The traces of these synthetic pulses are captured on an M-scan image and the transmitted data are decoded using image deconvolution and deblurring algorithms. Results: Using a chicken phantom and 1.3 MHz sonomicrometry crystals of diameter 1 mm, we first demonstrate that a standard ultrasound reader can achieve biotelemetry data rates up to 1 Mb/s for implantation depths greater than 10 cm. For this experiment the maximum power dissipation at the crystals was measured to be 20 μW and bit-error-rate of the telemetry link was shown to be 10^-2. We also demonstrate the use of this method for multiaccess biotelemetry where several sonomicrometry crystals simultaneously transmit the data using different modulation and coding techniques. Using a live ovine model, we demonstrate a sonomicrometry crystal implanted in the sheep 's tricuspid valve can maintain a continuous, reliable telemetry link at data rates up tob 800 Kb/s in the presence of respiratory and cardiac motion artifacts. Conclusion: Compared to existing radio-frequency and ultrasound based biotelemetry devices, the reported data-rates are significantly higher considering the transducer's form-factor and its implantation depth. Significance: The proposed technique thus validates the feasibility of establishing reliable communication link with multiple in vivo implants using M-scan-based ultrasound imaging.