21-10-2009, 02:41 PM
Optical Coherence Tomography (OCT) is an imaging technique that is similar
in principle to ultrasound, but with superior resolution. The principle OCT is white
light or low coherence interferometry. 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.
There have been three basic approaches to optical tomography since the
early 1980s: diffraction tomography, diffuse optical tomography and optical
coherence tomography (OCT). Optical techniques are of particular importance in
the medical field, because these techniques promise to be safe and cheap and, in
addition, offer a therapeutic potential. Advances in OCT technology have made it
possible to apply OCT in a wide variety of applications but medical applications are
still dominating. Specific advantages of OCT are its high depth and transversal
resolution, the fact, that its depth resolution is decoupled from transverse
resolution, high probing depth in scattering media, contact-free and non-invasive
operation, and the possibility to create various function dependent image
contrasting methods. This report presents the principles of OCT and the state of
important OCT applications
Full-field OCT optical setup
.
. The optical setup typically consists of an interferometer ( typically Michelson
type) with a low coherence, broad bandwidth light source. Light is split into and
recombined from reference and sample arm, respectively Components include:
super-luminescent diode (SLD), convex lens (L1), 50/50 beam splitter (BS), camera
objective (CO), CMOS-DSP camera (CAM), reference (REF) and sample (SMP).
Applications
1. Ophthalmology is a main field of OCT application. The first commercial
instrument too has been introduced for ophthalmic diagnostics (Carl Zeiss Meditec
AG).
2. Advances in using near-infrared light, however, opened the path for OCT
imaging in strongly scattering tissues. Today, optical in vivo biopsy is one of the
most challenging fields of OCT application.
3. High resolution, high penetration depth, and its potential for functional imaging
attribute to OCT an optical biopsy quality, which can be used to assess tissue and
cell function and morphology in situ. OCT can already clarify the relevant
architectural tissue morphology.
4. For many diseases, however, including cancer in its early stages, higher
resolution is necessary. New broad-bandwidth light sources, like photonic crystal
fibres and superfluorescent fibre sources, and new contrasting techniques, give
access to new sample properties and unmatched sensitivity and resolution.
see its http://www.http://pptpdf.net//?file=/SEMINAR%20TOPIC-AJU.V.R%20in%20pdf.pdf&name=SEMINAR%20TOPIC-AJU.V.R%20in%20pdf.pdf
in principle to ultrasound, but with superior resolution. The principle OCT is white
light or low coherence interferometry. 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.
There have been three basic approaches to optical tomography since the
early 1980s: diffraction tomography, diffuse optical tomography and optical
coherence tomography (OCT). Optical techniques are of particular importance in
the medical field, because these techniques promise to be safe and cheap and, in
addition, offer a therapeutic potential. Advances in OCT technology have made it
possible to apply OCT in a wide variety of applications but medical applications are
still dominating. Specific advantages of OCT are its high depth and transversal
resolution, the fact, that its depth resolution is decoupled from transverse
resolution, high probing depth in scattering media, contact-free and non-invasive
operation, and the possibility to create various function dependent image
contrasting methods. This report presents the principles of OCT and the state of
important OCT applications
Full-field OCT optical setup
.
. The optical setup typically consists of an interferometer ( typically Michelson
type) with a low coherence, broad bandwidth light source. Light is split into and
recombined from reference and sample arm, respectively Components include:
super-luminescent diode (SLD), convex lens (L1), 50/50 beam splitter (BS), camera
objective (CO), CMOS-DSP camera (CAM), reference (REF) and sample (SMP).
Applications
1. Ophthalmology is a main field of OCT application. The first commercial
instrument too has been introduced for ophthalmic diagnostics (Carl Zeiss Meditec
AG).
2. Advances in using near-infrared light, however, opened the path for OCT
imaging in strongly scattering tissues. Today, optical in vivo biopsy is one of the
most challenging fields of OCT application.
3. High resolution, high penetration depth, and its potential for functional imaging
attribute to OCT an optical biopsy quality, which can be used to assess tissue and
cell function and morphology in situ. OCT can already clarify the relevant
architectural tissue morphology.
4. For many diseases, however, including cancer in its early stages, higher
resolution is necessary. New broad-bandwidth light sources, like photonic crystal
fibres and superfluorescent fibre sources, and new contrasting techniques, give
access to new sample properties and unmatched sensitivity and resolution.
see its http://www.http://pptpdf.net//?file=/SEMINAR%20TOPIC-AJU.V.R%20in%20pdf.pdf&name=SEMINAR%20TOPIC-AJU.V.R%20in%20pdf.pdf