Breast Biopsy Analysis by Spectroscopic Imaging

Abstract

Short wavelength near infrared (SW-NIR) spectroscopy possesses many features that are advantageous for spectroscopic studies of tissue anatomy and physiology. Human tissue is relatively transparent in the 650–1300 nm spectral region so that relatively thick samples can be examined. At the same time one observes spectral features which arise from low lying electronic transitions of heme proteins and vibrational overtones from major constituents of tissue. As an example, reflectance oximetryl is based upon low energy electronic transitions of oxy and deoxyhemoglobin, Figure 1. The spectrum of the hemoglobin molecule is very different in the two forms. In oximetry, hemoglobin saturation is determined non-invasively by measuring the light scattered from tissue at 650 and 805 nm; the former wavelength represents a maximum in the absorbance difference between the oxy and deoxy forms while the latter represents an isosbestic point for the two forms. A substantial advance in oximetry was made by Yosohiya². In his scheme, recognition was taken of the fact that the light reflected from or transmitted through human tissue exhibits both a steady state (DC) and fluctuating (AC) signal. The former arises from tissue pigments and venous blood, while the latter arises from arteriole blood and fluctuates synchronously with the heart rate. Jobsis advanced the oximetry concept one step further. He noted that in addition to hemoglobin, copper in cytochrome oxidase, the terminal enzyme of the mitochondrial electron transport chain, could also be measured in tissue by SW-NIR spectroscopy. This work demonstrated the possibility that oxygen availability in the brain can be measured non-invasively by transillumination spectroscopy in the near infrared³. A major conceptual breakthrough in oximetry has recently been demonstrated by Chance⁴. Using time resolved pico-second spectroscopy Chance has measured localized hemoglobin dependance in tissues and has laid the foundation for NIR tomography of hemoglobin concentration and saturation.