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Optical
Coherence Tomography, or 'OCT', is a technique for obtaining
sub-surface images of translucent or opaque materials at a resolution
equivalent to a low-power microscope. It is effectively 'optical ultrasound', imaging reflections from within tissue to provide
cross-sectional images.
OCT is attracting interest among the medical community, because it
provides tissue morphology imagery at much higher resolution (better than
10 microns) than other imaging modalities such as MRI or ultrasound.
The key benefits of OCT are:
- Live
sub-surface images at near-microscopic resolution
- Instant,
direct imaging of tissue morphology
- No
preparation of the sample or subject
- No
ionizing radiation
OCT
delivers high resolution because it is based on light, rather than sound
or radio frequency. An optical beam is directed at the tissue, and a small portion of this light that reflects from sub-surface features
is collected. Note that most light is not reflected, but rather scatters off at large angles. In conventional imaging, this diffusely scattered light contributes
background that obscures an image. However, in OCT, optical coherence is
used to record the optical path length of received photons, allowing
rejection of most photons that scatter multiple times before detection.
Thus OCT can build up clear 3D images of thick samples by rejecting background signals while collecting light directly reflected from
surfaces of interest.
Within the range of non-invasive three-dimensional imaging techniques that
have been introduced to the medical research community, OCT as an echo
technique is similar to ultrasound imaging. Other medical imaging techniques such as computerised axial tomography, magnetic resonance
imaging, or positron emission tomography do not utilize the echo-location
principle.
Application:
Optical coherence tomography is an established medical imaging technique.
It is widely used to obtain high -resolution images of the anterior
segment of the eye and the retina, which can, for example, provide a
straightforward method of assessing axonal integrity in multiple
sclerosis, as well as macular degeneration. OCT is also a very reliable tool for monitoring
the progression of glaucoma.
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