As a result of Phase I researches, a perfected design of a simple, reliable and economical phase modulation system has been achieved. Desig parameter perturbation and component selection has lead to this simplified and reliable design of a dual wavelength time sharing phase modulation spectrometer (dual wavelength PMS). The frequency has been optimized at 200 MHz; time-sharing of the oscillator frequency between two diode lasers at different wavelengths, laser diode driver circuits, fiber optic coupling, standardized detector heterodyne njection, amplitude and sensitive phase detection circuit, together with time sharing demodulation are engineered. This instrument had undergone rigorous electromechanical tests and has a remarkable stability corresponding to a draft of less than 0.04degree/hr of phase drift and a noise level of 0.9 mm or approximately 0.2degree of phase. Tissue signals are of the order of 4 cm in amplitude and thus signal to noise ratios of 5:1 with a 5 sec time constant at 3 cm input/output distance are feasible. The remarkable features of time and frequency domain spectroscopy in providing the optical path length for photon migration in tissues is well recognized. Phase I set forth to exploit design parameters of a simplified system suitable for biomedical research and for clinical studies. Phase II will focus on construction of dual wavelength phase modulation systems that will bring to the clinic the advantages of TRs in an economical and feasible device. We propose to pursue product development and testing under Phase II support leading to commercial exploitation under Phase III; that is, production prototype, FDA approval, marketing and sales.
