Fundamental Study on Transcutaneous Biotelemetry Using Diffused Light

A new method of biotelemetry is proposed, which realizes nonrestrained acquisition of biological signals using the infrared light diffused out from animal skin. This technique is fundamentally different from conventional telemetry techniques which use radio-frequency electromagnetic waves. An optical transmitter which consists of some LED's is implanted beneath the skin. Biological information such as ECO signal is collected in vivo and the light emitted from the LED's is modulated by the signal. The light transmitted through the skin is strongly diffused and spread out in a wide angle. The light is collected by the remotely located optical receivers and the biological information is obtained by demodulating the signal. Thus, the biological information in vivo is obtained without restraining the object with cables or optical fibers. In order to verify the possibility of the above technique, a system, which obtains an ECG from laboratory animals, has been developed. An infrared light was chosen due to its invisibility and high transmittance through the skin. Considering the stability of the communication link and the power consumption of the implanted transmitter, PFM (Pulse Frequency Modulation) technique was used. Using the system, the transcutaneous ECG telemetry was performed successfully. In the experiment, the indirect light reflected and scattered by the walls, the ceiling and the floor was shown to be useful in the optical telemetry. Light transmission patterns through the skin of a mouse were measured. The results suggest the possibility of telemetry even from the deep part of the body cavity. It is concluded that recent progress of optical and electronic technologies have reached the point, where transcutaneous optical telemetry of biological signals has become practically possible.