Transabdominal fetal oximetry based on frequency-modulated continuous-wave near-infrared spectroscopy

A frequency-modulated continuous-wave (FMCW) time-domain near-infrared spectroscopy system, the system comprising:

• a first frequency-modulated light source to generate a first probe light having a central wavelength of λ1;
• a second frequency-modulated laser source to generate a second probe light having a central wavelength of λ2;
• an interferometer configured to determine a time-resolved reflectance curve for each of the first probe light and the second probe light during a fetal oximetry, wherein the interferometer further comprises:
• a splitter configured to split the first probe light into a first reference light and a first sample light and the second probe light into a second reference light and a second sample light;
• a guiding mechanism configured to guide the first probe light and the second probe light to probe a maternal-fetal multilayer tissue structure, thereby generating a first band of light signals and a second band of light signals carrying information of the maternal-fetal multilayer tissue structure;
• and
• a coupler configured to receive and mix the first and second reference lights with the first and second bands of light signals, respectively to effectuate an interference between the first or the second reference light and the first or second band of light signals to produce a band of beat frequencies;
• and
• a processing unit configured to generate a time-resolved reflectance curve based on the band of beat frequencies.

A frequency-modulated continuous-wave (FMCW) method for non-invasively measuring a fetal blood oxygenation level, comprising:

• using a first wavelength swept laser source to generate light having a central wavelength λ1;
• using a second wavelength swept laser source to generate light having a central wavelength λ2;
• using an interferometer to determine a time-resolved reflectance for each of the two central wavelengths λ1 and λ2 by:
• splitting light from the first and second swept laser sources between a reference arm that has a known distance, and a sample arm that directs light into a maternal abdomen of a pregnant mammal toward a fetus, and returns reflected light that is coupled from different detection locations on the maternal abdomen;
• combining light from the reference and sample arms to produce time-domain interference fringe patterns;
• and
• calculating the time-resolved reflectances based on the time-domain interference fringe patterns;
• determining absorption coefficients and/or reduced scattering coefficients for the fetal tissue for both central wavelengths λ1 and λ2 by fitting the time-resolved reflectances to a tissue model for maternal tissue and fetal tissue based on known source-to-detector distances;
• and
• performing a pulse-oximetry computation based on the determined absorption coefficients to determine the fetal blood oxygenation level.