Quantitative and Qualitative Evaluation of Dental Structures using Multispectral Photothermal Diagnostic Techniques

Enhanced Truncated-Correlation Photothermal Coherence Tomography (eTC-PCT) is a dynamic frequency-domain imaging modality for non-invasive imaging of samples. The original embodiment of eTC-PCT uses an 808-nm diode laser to generate 3D photothermal images of samples. In order to obtain molecular specificity in biological samples based on their absorption and scattering properties, in this thesis, the eTC-PCT has been improved and multispectral TC-PCT imaging technique has been developed which employs an Nd:YAG pulsed laser that pumps an optical parametric oscillator (OPO) for wavelength tunability. Multispectral TC-PCT is then used for 3D photothermal imaging of natural and artificial early dental caries. Results have shown that near-surface and deep subsurface defects within the tooth can be imaged as a function of wavelength. These results hold importance as other active thermography methods such as eTC-PCT have not achieved similar outcomes. This makes multispectral TC-PCT a promising approach for expanding its applications in imaging both hard and soft tissues, provided the appropriate wavelength is selected.To complement the experimental work in relation to the photothermal signal detected during multispectral TC-PCT imaging, a theoretical model of pulsed photothermal radiometry based on conduction-radiation theory is developed for two-layered samples followed by a controlled experimental approach. After validating the developed theory for two-layered samples through a controlled experiment, biological samples such as teeth are used. Teeth contain both absorption and scattering coefficients which allow for the quantitative examination of how the optical and thermal properties of healthy and carious enamel vary depending on the excitation wavelength. Through the utilization of both the theoretical framework and experimental findings, the optical and thermal parameters of healthy and carious teeth across the various wavelengths are measured leading to the determination of the degree of reliability of each of the fitted parameters. For the first time, pixel-by-pixel images depicting the essential optical and thermophysical parameters of dental structures are shown. This enables the creation of a precise calibration chart, empowering the identification and extent of caries in a tooth. This innovative method has the potential to improve how dental health is understood and diagnosed in a more concrete and measurable way.

Department dc:contributor.department

Mechanical and Industrial Engineering

Year dc:date.issued

2024

Author dc:creator

• Baradaran Shokouhi, Elnaz

Advisor dc:contributor.advisor

• Mandelis, Andreas

• Active Thermography
• Laser Engineering
• Non-destructive Testing
• Photonics

Handle dc:identifier.uri

http://hdl.handle.net/1807/138093

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/138093