1. Photothermal spectroscopy Rotem Neeman & Yonat Milstein
under the supervision of Prof. Israel Gannot, Dr. Moshe Ben David & Michal Tepper
The Lasers & Optics in Medicine Laboratory, Department of Biomedical Engineering , Faculty of Engineering, Tel Aviv University
1. Introduction
Spectroscopy of biological tissues is a powerful tool for evaluation of tissue composition and functionality.
Photothermal spectroscopy is a method for performing tissue spectroscopy, based on measuring tissue thermal changes due to light excitation.
Using this method allows estimating the tissue’s oxygenation level, which is a significant value.
The algorithm- stage 1
The temperature is estimated using a curve fitting algorithm
Tstart
Tsaturation
2. Objective
Developing a thermal imaging method to determine the oxygenation level of a tissue.
Developing an ideal measuring method.
Evaluating an existing algorithm for measurement analysis.
The algorithm- stage 2
The temperature increase, ΔT, is normalized according to intensity
3. The method
Illuminating a tissue by a laser will cause a temperature increase.
The temperature increase depends on tissue composition, its optical properties and the exciting laser wavelength.
Using several wavelengths for the excitation will allow us to estimate tissue composition.
The algorithm- stage 3
There is a linear relation between the temperature difference and the effective absorbance.
Laser
Tissue
S, the blue material ratio, is unknown and will be estimated using the curve fitting algorithm.
Materials: Methylene Blue, Indocyanine Green (ICG).
Setup: Ti:Sapphire laser, ThermoVision A40 IR thermal camera.
5. Results
1-layer phantoms
4. The Experiment
RMS=5.26%
RMS=9.03%
Creating phantoms using different ratios of the two absorbers
Illuminating the phantom
Phantom is heated and the temperature is measured
Running a computational algorithm   
Absorbers ratio is estimated
2-layer phantoms
RMS=3.61%
Creating the phantoms using various concentrations of the two materials mixed with agar.
Using phantoms with an upper absorbing layer, ink, which simulates a complex tissue.
Illumination the phantoms in different wavelengths.
The rise in the temperature is measured.
6. Conclusions
We were able to determine a good measuring method.
The algorithm was able to estimate the phantoms composition relatively well, all experiments had an error RMS lower then 10%.
The main problem we encountered was the sensitivity of the measurements to environmental changes which affected the results.