Quantitative Measurements in Scattering Media: Path length Determination of Short Wavelength Near Infrared Light in Fish Tissue
EMSL Project ID
2284
Abstract
The objective of this study is to understand and evaluate how near infrared light penetrates through fish tissue. This fundamental study is necessary to improve the application of near infrared spectroscopy to the development of non-invasive methods of analysis. Over the past five years I have worked on projects such as measuring lipid content in live fish, predicting maturity status and gender in salmonids and investigating the possibility of measuring sodium chloride and moisture in caviar and other cured fish products. The spectroscopic approach to all these projects is based on a diffuse reflectance measurement. The near infrared light is launched into the tissue by several illuminating fiber optics located at the end of a flexible probe, it is diffusely reflected through the different tissue layers and is collected by a collecting fiber optic located in the center of the probe. The volume of sampled tissue in any case is limited by how far the light penetrates into the sample. For example if lipid content in fish muscle is to be analyzed, one has to be sure that the light penetrates through the skin and the scales and actually reaches the desired area. In addition to the penetration issue, there are also non-linear effects that are generated by scattering phenomena. Fish tissue is a highly scattering medium, so when light travels through it, it is continuously deviated. This confounds the spectral information that comes from a specific analyte, in this case lipid, and introduces non-linearities which are not well handled by conventional calibration methods. Most investigators have tried to correct scatter with multiwavelength steady-state methods using preprocessing tools to correct or reduce the scattering contribution in the spectra prior to analysis. One approach is to ratio the whole spectrum to one or more specific wavelength. Others include a first or second derivative or multiplicative signal correction. Attempts to linearize my data by applying any of these strategies did not yield significant improvements. Few investigators have tried to solve the problem with a more fundamental approach, which uses information associated with absorption and scatter in the sample at a single wavelength. Dr. David Burns at McGill University in Canada has pioneered an experimental approach which uses photon time-of-flight measurements to estimate the distance a photon travels through a given scattering sample. By analyzing the photon time distribution he can estimate the absorption coefficient ma and the scattering coefficient ms. These can in turn be used to describe the light propagation in a medium by solving the time-dependent diffusion equation. Alternatively the absorption and scattering coefficients can be used to correct the experimental absorbance. This approach, according to Dr. Burns, yields the best linearization results. We propose to conduct time-of-flight measurements in Dr. Zheming Wang's laboratory to estimate absorption and scattering coefficients of fish tissues with different lipid and salt concentrations. Measurements will be performed on minced samples as well as slabs of known thickness. All samples will be prepared at Eastern Oregon University and analyzed in Dr. Wang's laboratory. We wish to conduct this research as a collaborative effort and involve Dr. Wang in all aspects of dissemination of any results obtained.
Project Details
Project type
Exploratory Research
Start Date
2001-08-01
End Date
2004-07-19
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Wutzke J, C Fahlstrom, AG Cavinato, Z Wang, M Lin, and B Rasco. 2004. "Investigation of Near-Infrared Optical Parameters in Fish Tissue by Photon time-of-Flight Analysis." THE AMERICAN CHEMICAL SOCIETY , Bellingham, WA.