Optics 101

Optical Coherence Tomography - An Introduction to Optical Coherence Tomography

Introduction
Optical Coherence Tomography - How does it Work?
Optical Coherence Tomography - An Imaging Tool

Introduction

Optical Coherence tomography has been used for a number of applications such as biomedical and materials research for the past decade. Optical coherence tomography can be considered as a new kind of medical and diagnostic imaging technology which uses fiber optics and advanced photonics to obtain an image.

Optical Coherence Tomography - How does it Work?

Optical coherence tomography uses a combination of visible aiming beam and light from a broadband, near-infrared source, which are then coupled into a single branch of a fiber-optic Michelson interferometer. Superluminescent diodes, femtosecond pulse lasers, and fiber amplifiers can be used as the broadband light source.

A 2x2 coupler is utilized to split the light into two fibers. One fiber focuses into the tissue while the second one leads to a reference mirror. Light reflected off the reference mirror is then re-coupled into the fiber leading to the mirror. At the same time, light reflected from a mismatch in refraction index in the tissue is re-coupled into the fiber leading to the tissue. Light which has been back-reflected from the reference arm and from the tissue are recombine within the 2 × 2 coupler.

An optical detector is used to detect the interference between the tissue and reference. During the imaging process, the reference-arm mirror is scanned at a constant velocity. This allows for depth scans to be made. Either the interferometer optics or the tissue is mounted on a stage; this allows the beam to scan laterally across the tissue to generate a pixel by pixel two- and/or three-dimensional images.

Optical Coherence Tomography - An Imaging Tool

Techniques such as ultrasound, magnetic resonance imaging, positron emission tomography and x-ray computed tomography have been employed in many clinical areas. These techniques measure the difference in physical property and possess a penetration range and resolution which is useful for specified applications.

On the other hand, optical coherence tomography provides a 1 to 15 µm resolution but only a depth of 1 to 2 mm can be imaged in opaque tissues such as arteries or skin. In transparent tissues such as the eye, greater imaging depths are possible.

Although severely limited by the depth of penetration, optical coherence tomography imaging can be carried out in real time and at a similar distance of a biopsy. In addition, optical coherence tomography is capable of providing information about tissue composition. The spectral absorption characteristics of tissues can also be studied using spectroscopy at the same time using polarization imaging to determine the orderliness of the tissue.

Source: AZoOptics

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