Date of Award
Master of Science in Biomedical Engineering - (M.S.)
Tara L. Alvarez
Light has been used extensively in the medical field for both therapeutic and diagnostic applications. Tissue optical window or therapeutic window defines the range of wavelengths where the light has the maximum transmittance through tissue. In this range, absorption and scattering effects are relatively lower when compared to the visible or middle infrared wavelengths. Knowledge of the transmittance through tissue can help determine the effective light intensities in medical applications.
The objective of this thesis is to determine the NIR light transmission through different thicknesses of animal tissue and its spatial spread due to the scattering effect. Primarily pork skin and muscle tissues are used due to their similar optical properties to human tissue. Tissue thicknesses range from 4 mm to 20 mm. A NIR LED array with the wavelength of 875 nm serves as the light source. A commercial photodiode is used for measurements of the transmitted light intensities.
The results demonstrate a transmittance of 18% for 4 mm tissue thickness and 3% for 20 mm and vary exponentially in between. Scattering increases the spatial spread of the light beam and makes it very difficult to focus inside the tissue. In addition to the transmittance measurements, temperature elevation due to the NIR light illumination is investigated. Thermocouple measurements show a temperature increase of 1.2 °C on the surface of the tissue slab at the light intensities tested in this project.
Ozgulbas, Deniz, "NIR light transmission through skin and muscle" (2013). Theses. 164.