Optical imaging techniques that provide free space, label free imaging are powerful tools in obtaining structural and biochemical information in biological samples. To date, most of the optical imaging technologies create images with a specific contrast and require multimodality integration to add additional contrast. In this study, we demonstrate spectroscopic Thermo-elastic Optical Coherence Tomography (TE-OCT) as a potential tool in tissue identification. TE-OCT creates images based on two different forms of contrast: optical reflectance and thermo-elastic deformation. TE-OCT uses short laser pulses to induce thermo-elastic tissue deformation and measures the resulting surface displacement using phase-sensitive OCT. In this work we characterized the relation between thermo-elastic displacement and optical absorption, excitation, fluence and illumination area. The experimental results were validated with a 2-dimensional analytical model. Using spectroscopic TE-OCT, the thermo-elastic spectra of elastic phantoms and tissue components in coronary arteries were extracted. Specific tissue components, particularly lipid, an important biomarker for identifying atherosclerotic lesions, can be identified in the TE-OCT spectral response. As a label-free, free-space, dual-contrast, all-optical imaging technique, spectroscopic TE-OCT holds promise for biomedical research and clinical pathology diagnosis.

We exploit the thermoelastic effect to acquire spectroscopic information which is based on the inherent tissue optical absorption properties. We support the acquired data with a 2D model along with system characterisation.

The absorption of laser pulses by tissue leads not only to the generation of acoustic waves, but also to nanometer to sub-micrometer scale displacement. After the initial expansion, a quasi-steady state is achieved in a few microseconds. Previously we introduced the concept of thermo-elastic optical coherence tomography (TE-OCT) to "visualise" the rapid thermo-elastic expansion by measuring the Doppler phase shift rather than istening" to the acoustic wave as in photoacoustic imaging. In this study, we built a microscopic setup for high-speed 3D TE-OCT imaging, by means of thermo-elastic optical coherence microscopy (TE-OCM). The repetition rate of pulsed laser was set to 100 Hz and the line rate of the OCT system is 1.5 MHz. The OCT beam and the laser pulse were focused upon the same location on the sample FWHM spot sizes of 300 μm for the pulsed laser and 40 μm FWHM for the OCT beam. For each laser pulse, an M-mode OCT image consisting of 90 A-lines was acquired. The Doppler phase shift was extracted by comparing the phase signal before and after the pulse arrival. Within 6 minutes, a 3D TE-OCM image (10 × 10 × 4 mm³) can be acquired and processed. Imaging experiments were carried out in swine meat using 1210 nm excitation wavelength to highlight lipid in tissue. The results show that no significant displacement was detected in swine muscle while strong displacement was observed in lipid, owing to the optical absorption features. Furthermore, fatty tissue is easily identified in the 3D TE-OCM image while the conventional OCT images provides the structural information.