Real-time multi-channel Fourier transform spectroscopy and its application to non-invasive blood fat measurement

• Hundreds times more sensitive than conventional polychromators.
• Substances in blood can be measured in real time.

We developed a real-time multi-channel Fourier transform spectrometer with an area sensor to track biological sample motion. In order to decrease the time intervals between measurements, a simultaneous measurement system consisting of two interferograms with opposite phases was constructed by using an area sensor instead of the often-used linear sensor. Since this system requires no mechanical motion for measurement, the rate at which it outputs spectra depends only upon the frame rate of the area sensor. This spectrometer was employed in the near-infrared region at wavelengths of 900–1700 nm to realize non-invasive blood testing. Substances in blood can be measured at 20 Hz using this method, which is higher than the pulse rate of a human blood vessel. This high-frequency technique enables the extraction of only the blood spectra from samples obtained from fingertips. In this study, the concentration of neutral fat within the blood was determined by extracting the periodically changing signal from the 1200 nm peak.