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RMS=9.03% . RMS=3.61%. RMS=5.26% . Photothermal spectroscopy. Rotem Neeman & Yonat Milstein under the supervision of Prof. Israel Gannot, Dr. Moshe Ben David & Michal Tepper

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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



  • 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.



  • 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

2-layer phantoms

  • 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.

  • The rise in the temperature is measured.
  • Illumination the phantoms in different wavelengths.
  • 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.