Mini-FDPM and heterodyne mini-FDPM: handheld non-invasive breast cancer detectors based on frequency-domain photon migration

This paper describes a handheld instrument for noninvasive detection of breast cancer based on a broad-band optical spectroscopy technique called frequency-domain photon migration (FDPM). It performs broad-band modulation on the intensity of near-infrared laser diodes and derives the scattering and absorption coefficients of the bulk tissue from phase and amplitude data measurements. Two different schematics of mini-FDPM were designed and fabricated. One is a homodyne structure that performs direct comparison of modulated and demodulated frequencies, and the other is a heterodyne structure that compares downconverted demodulated frequencies. The former has a simple structure but lower accuracy due to noise. The latter is more complex but more accurate due to the filtering of noise. The miniature size makes it possible to eliminate fiberoptic cables and enables direct contact between the laser diode and the tissue, making the instrument more power efficient while enhancing detection capabilities. Measurement results show that these miniature systems match or outperform the current prototype while costing two orders of magnitude less.