Fiber optic probes for biomedical optical spectroscopy

Abstract

Optical spectroscopy has been well validated by the physical sciences as a method to characterize chemical compositions in biological material. It has also showed promising to detect atherosclerotic plaques, which can form in the coronary artery walls, and cause heart attacks and strokes. This project seeks to optimize and build fiber optic probes for diffuse reflectance and fluorescence spectroscopy which can assess these plaques. A side-viewing probe is particularly advantageous in the small diameter, confined geometries of arteries. Thus, different techniques are investigated for creating lenses on the tip of optical fibers and design the probes so that they can perform spectroscopic measurements along its circumference. A rigorous testing scheme was developed which included a test matrix and a set of criteria that were used in the optimization process. Two probes for diffuse reflectance and one for fluorescence measurements were built based on the result from the testing scheme. However, a combined probe optimized for both diffuse reflectance and fluorescence measurements could not be created as their respective optimization criteria turned out to be contradictory. The final reflectance probes consisted of two 200 micron fibers separated by 2 mm in the axial direction and the fiber tips were shaped by using a CO2 laser and grinding machine. All the finished probes were tested in a coronary artery of a porcine heart and fat was injected to evaluate their detection of lipid pools. The probes showed good results and were able to detect changes in chromophore content in the tissue and demonstrated the advantages of optimizing a probe for its given application. The fluorescence probe turned out to give good results when used on the arteries from the surface of the heart surface.