Hybrid System

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 pHOS) 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 proposed method

1. uses a multi-distance frequency domain (MDFD) system to measure the absorption coefficient (μ_a) and the reduced scattering coefficient (μ_s’) of tissue at a selection of discrete wavelengths,
2. assumes a wavelength dependence of scattering and calculate μ_s’ over all wavelengths in the spectral window of interest and
3. 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_s’ across 200 wavelengths.

Figure 1. MDBBS configuration

Figure 2. MDFD system Figure 3. Optode holder combination

For further information you can have a look at Dr Ilias Tachtsidis OSA BIOMED 2008 poster [Poster Link] and OSA BIOMED 2010 oral presentation [Presentation Link]. For enquires you contact directly Dr Ilias Tachtsidis [email]. 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.” in Biomedical Optics OSA Technical Digest (CD) (Optical Society of America, 2008), paper: BSuE76. [URL] [PDF]The pHOS operation has been tested extensively using optical phantoms [1,2] and we have recently reported on the use of the system in healthy volunteers [3].

References

1. Tachtsidis I., Gao L., Leung T.S., Kohl-Bareis M., Cooper C.E., Elwell C.E. “A hybrid multi-distance phase and broadband spatially resolved spectrometer and algorithm for resolving absolute concentrations of chromophores in the near-infrared light spectrum.” Advances in Experimental Medicine and Biology (2010) 662:169-175. [URL] [PDF]
2. Tachtsidis I., Leung T.S., Ghosh A., Smith M., Cooper C.E., Elwell C.E. “Multi-Wavelength, Depth Resolved, Scattering and Pathlength Corrected in vivo Near-Infrared Spectroscopy of Brain Tissue.” in Biomedical Optics OSA Technical Digest (CD) Optical Society of America, 2010) paper: BTuB7. [URL] [PDF]