Hybrid Optical Spectrometer

In cranial near-infrared spectroscopy (NIRS) the quantification of brain tissue chromophores requires high depth sensitivity and the ability to separate the effects of absorption from those of scattering. Haemoglobin, water and cytochrome-c-oxidase are known tissue chromophores in the near-infrared (NIR) region, but their absolute concentrations vary between individuals. It is also likely that other important chromophores, such as fat, may make a significant contribution to the non-haemoglobin absorption. The Hybrid Optical Spectrometer (or HOS) is a novel optical instrument built to exploit a combination of optical techniques to achieve high absolute quantification and depth resolved information of the intrinsic chromophores of the adult brain tissue. The design of the instrument is intended to enable as much information to be extracted as possible from measurements of light transmitted across large thicknesses of tissue.Our propose method (i) uses a multi-distance frequency domain (MDFD) system to measure the absorption coefficient (μ_a) and the reduced scattering coefficient (μ_st) of tissue at a selection of discrete wavelengths, (ii) assumes a wavelength dependence of scattering and calculate μ_s’ over all wavelengths in the spectral window of interest and (iii) uses a multi-distance broadband spectrometer (MDBBS) to measure the light attenuation and light attenuation slope over a wide spectral range and at a number of source detector spacings. This information is fused together to provide absolute μ_a and μ_st across 200 wavelengths. ^[1]

	Figure 2. MDFD system
	Figure 3. Optode holder combination
Figure 1. MDBBS configuration	Video demonstration of system operation

The development of HOS and the performance of experimental and clinical studies has been generously supported by grants from the EPSRC.

References
[1] Tachtsidis I., Kohl-Bareis M., Leung T. S., Gramer M., Tahir B., Cooper C. E., Elwell C.E., “A hybrid multi-distance phase and broadband spatially resolved algorithm for resolving absolute concentrations of chromophores in the near-infrared light spectrum: application on to dynamic phantoms.” Biomedical Topical Meetings (The Optical Society of America), BSuE76, Florida, USA  (March 2008). Click here for details.