UCLA

Near infrared spectroscopy [NIRS] is a non-invasive, non-ionizing imaging technique that uses light in the 650 nm to 2,500 nm region of the electromagnetic spectrum. In medical applications, optical devices utilize what is known as the biologic window (i.e. "therapeutic widow"). This window encompasses the light from 600 nm to approximately 1,400 nm. The reason why many medical optical devices exploit light sources within this spectrum is that tissue proteins are relatively transparent at these wavelengths with the exception of certain chromophores such as oxygenated and deoxygenated hemoglobin, fat, and water. However, light is highly scattered by the tissue and this scattering phenomena must be considered when obtaining information at depth within tissues. Thus, good penetration of light into the tissue and investigation of chromophores of interest at various depths is possible but requires careful modeling and understanding of light scattering at given depths. Since their introduction, medical NIRS devices have been used in many physiologic monitoring applications, including, pulse oximetry, functional NIR for measuring the neuronal activity in the brain, measurement of oxygen consumption in skeletal muscles, and more recently the measurement of tissue blood perfusion.

This dissertation investigated a hypothesis that multi-channel depth-resolved near infrared spectroscopy can be used to monitor lower leg tissue oxygenation and lower leg oxygenation abnormalities and that depth-resolved data collection will provide useful information for analyzing the oxygenation state of tissue. The work presented here details development of a novel portable multi-channel NIRS system capable of long-term non-invasive monitoring of lower leg tissue blood oxygenation levels. Twenty two healthy subjects took part in the feasibility study of the novel system. The study examined the performance of the novel NIRS system in acquiring depth resolved multi-channel data from control leg and test leg, which was subjected to 60-second venous occlusion. The results showed that: The system is capable of acquiring statistically significant multi-channel NIRS data during venous occlusion with or without baseline data; and depth-resolved data provides significant information for analyzing oxygenation state of tissue. These findings indicate that the novel multi-channel depth resolved near infrared spectroscopy system could be used for lower leg tissue oxygenation monitoring.