Optical Coherence Tomography

Abstract

This paper explains the state of the art optical coherence tomography as an efficient diagnostic imaging tool for biomedical applications. It reviews the basic theory and modes of operation together with its applications and limitations. It also examines the various kinds of instruments, which are employed in the whole apparatus, in addition to a discussion on hardware and software methods to combat the sources of error.

Types of OCT

There are also other types of OCT which are also utilize light to produce imaging of tissue however they tend to include or vary the components of the system to provide more emphasis and extract more information from scans based on something specific from the sample. One of these ideas is the Doppler OCT which looks from for frequency shifts in the interference patterns which would show moving objects in the sample such as blood cells. This is particularly interesting to ophthalmologists since variations in blood flow can be causes of blindness, including diabetic retinapothy and macular degeneration . In addition to Doppler OCT, researchers are also looking into polarization which would measure the polarization of returning light and interference fringes since this might be a way to image damage to tissue such as nerve fibers, skin, and other connective tissues.

Light Source

The light source itself should satisfy three basic requirements, i.e., emission in near infra-red spectrum region, having short coherence length and high irradiance. Because of short mean scattering length for high frequencies (blue and higher), longer wavelengths are highly desired. On the other hand, due to strong water absorption for wavelengths.

Speed

As important as the resolution is the speed of an OCT system. The frame rate is basically determined by the speed with which the path-length could be swept, in order to obtain a complete cross correlation function. A new technique has also been introduced recently by the employment of grating-based phase control delay . The Fourier transform is generated on the grating upon incidence of the reference beam. The scattered wave is then directed to a linear wavelength dependent phase ramp, and since linear phase ramp in the frequency domain stands for group delay in time domain, when the signal is incident on the grating for the second time, the inverse Fourier transform is generated.

Introduction

OCT has been mainly used for biomedical applications where many fac¬tors affect the feasibility and effectiveness of any imaging technique. The highly scattering as well as absorbing living tissues greatly limit the applica¬tion of optical imaging modalities. Other imaging methods, such as ultrasonic has been used for a long time, yet each of them have certain problems and limitations. For instance, albeit ultrasonic technique can provide informa¬tion from depths far beyond the capability of OCT, in many applications the resolution is not satisfactory to result in any useful information.

Conclusions

Optical coherence tomography (OCT) has been emerged a novel diagnostic tool for bio medical applications, especially in situations where conventional imaging methods are either hazardous or of little valuable information.