Thermal Emission Decay FTIR Spectroscopy and Phantom Studies for In-vivo Skin Research

The new technique of Thermal Emission Decay Fourier Transform Infra-Red Spectroscopy (TED-FTIR) has been developed to measure depth resolved thermal emission spectra from localised areas on arbitrary samples without contact with the sample, and without sample preparation. The instrument is based on a combination of Opto-Thermal Transient Emission Radiometry (OTTER) and step-scan Fourier Transform spectroscopy techniques.
The theoretical basis for the technique is described and criteria for the design of an instrument based on a commercial Fourier Transform spectrometer discussed. The performance of the instrument was evaluated by comparing the measured spectra from homogeneous and layered samples with the spectra of the same materials measured using more established techniques.
Attempts were made to measure spectra from skin in-vivo, the main focus for this work. The reasons why the signal to noise ratio of the current instrument is poor for such measurements are explained. Improvements to the instrument to overcome these problems are discussed, along with other improvements to enhance the capabilities of the instrument.
In a second aspect to this work, factors which affect the rise time of delayed peaks in opto-thermal signals were investigated experimentally using physical models (phantoms) which mimic some of the properties of skin. The rise time of these peaks had been proposed as a means of calculating the thickness of the epidermis.
Factors influencing the design and use of such phantoms is discussed both in general terms and for the specific system. The results from these experiments have identified several properties which have minimal effect on the rise time of the peaks. They have also highlighted the limitations of phantoms for mimicing skin.