Optical Coherent Tomography

In an effort to provide more detailed information about epileptic lesions in neural tissuefor the purpose of efficient removal, an Optical Coherence Tomography system was built to provide non-destructive imaging. The device is based upon the principle of a low-coherenceinterferometer. Such an instrument can detect if a particular point within a sample of tissue reflects light; an integration and interpretation of many scans of many points provides a highresolution image. The device built for this investigation has been successful in scanning semi-reflectiveobjects such as glass and glossy plastic. Objects with low reflectivity or high degrees of scattering did not produce strong enough signals to be detected successfully. One-dimensional scans were accomplished with reasonable speed and under computer control. Limited twodimensional scans were also taken with much lower speed and with constant human intervention. Optical Coherence Tomography (OCT) is an imaging technique that is similar in principle to ultrasound, but with superior resolution. It relies on exposing a sample to a burst of light and then measuring the reflective response from different depths and is therefore capable of scanning non-invasively beneath the surface of the sample. In ultrasound imaging, it is relatively easy to measure the time delay of each reflected packet. However, for light pulses, interferometry must be used to measure the displacement with meaningful accuracy. The amount of light reflected from each point within the scanning window in the sample is plotted graphically as an OCT image. The goal of this investigation is to use Optical Coherence Tomography to image epileptic lesions on cortical tissue from rats. Such images would be immensely useful for surgical purposes. They would detail how deep the lesion is, allowing for precise removal that neither removes an insufficient amount of damaged tissue nor extracts too much healthy tissue. Though commerical OCT systems already exist, they typically do not scan very deeply beneath sample surfaces. For the purpose of this study, a system must be constructed that scans up to 2 millimeters into tissue1. Unfortunately, an increase in axial depth necessitates a decrease in transverse (along the surface of the sample) resolution due to focal restrictions of the objective lenses2. However, this loss is acceptable for this investigation, as the main goal is to determine lesion depth and not to achieve perfect image clarity