Absorption spectral imaging in the mid-infrared and its application in cancer diagnosis

Abstract

This thesis presents work on the development of two distinct systems for the purpose of spectral imaging in the mid infrared (MIR), with particular focus on a method than can be of use in cancer diagnosis. Wavelengths are used that correspond to positions of absorbance peaks from the vibrational modes in molecules commonly found in biological tissue. Images from different wavelengths are combined to show the relative concentration of nuclei in tissue, an accepted marker of malignancy that can be seen in cancerous cells. One system, we have termed the “digistain” system, uses a thermal source with narrow bandpass filters to select the wavelength, the other uses a pulsed tuneable quantum cascade laser (QCL) unit. Both systems show results that highlight a difference between healthy epithelium and epithelium that has entered a pre-cancerous stage. The digistain system has benefits in speed over other infrared spectral imaging systems, such as a scanning Raman system or a commercial multi-channel Fourier transform infrared (FTIR) system. Before a reliable direct comparison of the quantitative results of the digistain to histological grading of the same areas can be made, a method to identify the different tissue types that are present and mixed together must be created. The QCL system was also used for diffuse reflection imaging, with the conclusion that the differing surface roughness of the samples investigated played a larger role in creating contrast between areas of different chemical composition than did absorption.