Tissue temperature by near-infrared spectroscopy

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Abstract
Optical determinations of tissue temperature by near-infrared (NIR) spectroscopy provides the basis for measuring localized changes in tissue metabolism associated with congnition, mechanical work, inflammation, or malignancy. Absorbance changes in NIR spectra of tissue water are shown to correlate with tissue sample temperature. Digital tissue transmission spectra of samples 1-5 mm thick of bovine and avain muscles were obtained over temperatures ranging from 17 to 45C. Reflectance spectra were obtained from blocks of porcine muscle over the temperature range 14 to 46C. Multilinear regression analysis of the correlation between absorbance or reflectance and tissue temperature demonstrated that each O-H bond onvertone spectral region (960, 1200, 1450, and 1920 nm) has a high correlation with tissue temperature. Transmission results gave standard error of the estimates (SEE) and standard error of prediction (SEP) from cross-validation analysis of 0.02 to 0.12C for SEE and 0.04 to 0.12C for SEP. Reflectance results gave SEEs of 0.06 to 0.24C. Combinations of O-H vibrational modes of water give rise to NIR absorbance in solution and tissue. The spectra show a regular shift to shorter wavelength absorbance as temperature increases. Such shifts may be due to decreasing hydrogen-bonding with increasing temperature. These studies have established that the temperature dependent changes in water NIR spectra can be utilized to evaluate tissue temperature with precision and accuracy.

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