Optical tomography
Encyclopedia
Optical tomography is a form of computed tomography
that creates a digital
volumetric model of an object by reconstructing images made from light transmitted and scattered through an object. Optical tomography is used mostly as a form of research in medical imaging
.
Optical tomography relies on the object under study being at least partially light-transmitting or translucent, so it works best on soft tissues; imaging of breast
and brain
tissue are examples.
The high scatter-based attenuation involved is generally dealt with by using intense, often pulsed or intensity modulated, light sources, and highly sensitive light sensors, and the use of infrared
light at frequencies where body tissues are most transmissive. Soft tissues are highly scattering but weakly absorbing in the near-infrared and red parts of the spectrum, so that this is the wavelength range usually used.
One recent variant of optical tomography uses optical time-of-flight sampling as an attempt to distinguish transmitted light from scattered light. This concept has been used in several academic and commercial systems for breast cancer imaging and cerebral measurement. The key to separation of absorption from scatter is the use of either time-resolved or frequency domain data which is then matched with a diffusion theory based estimate of how the light propagated through the tissue. The measurement of time of flight or frequency domain phase shift is essential to allow separation of absorption from scatter with reasonable accuracy.
A more recent development since about the year 2000, has been the development of systems for fluorescence tomography of tissue. In these systems, the fluorescence signal transmitted through the tissue is normalized by the excitation signal transmitted through the tissue, and so many of the fluorescence tomography systems do not require the use of time-resolved or frequency domain data, although research is still ongoing in this area. Since the applications of fluorescent molecules in humans are fairly limited, most of the work in fluorescence tomography has been in the realm of pre-clinical cancer research. Both commercial systems and academic research have been shown to be effective in tracking tumor protein expression and production, and tracking response to therapies.
Optical tomography found its application in industry as a sensor of thickness and internal structure of semiconductors .
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
that creates a digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
volumetric model of an object by reconstructing images made from light transmitted and scattered through an object. Optical tomography is used mostly as a form of research in medical imaging
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
.
Optical tomography relies on the object under study being at least partially light-transmitting or translucent, so it works best on soft tissues; imaging of breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
and brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
tissue are examples.
The high scatter-based attenuation involved is generally dealt with by using intense, often pulsed or intensity modulated, light sources, and highly sensitive light sensors, and the use of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
light at frequencies where body tissues are most transmissive. Soft tissues are highly scattering but weakly absorbing in the near-infrared and red parts of the spectrum, so that this is the wavelength range usually used.
One recent variant of optical tomography uses optical time-of-flight sampling as an attempt to distinguish transmitted light from scattered light. This concept has been used in several academic and commercial systems for breast cancer imaging and cerebral measurement. The key to separation of absorption from scatter is the use of either time-resolved or frequency domain data which is then matched with a diffusion theory based estimate of how the light propagated through the tissue. The measurement of time of flight or frequency domain phase shift is essential to allow separation of absorption from scatter with reasonable accuracy.
A more recent development since about the year 2000, has been the development of systems for fluorescence tomography of tissue. In these systems, the fluorescence signal transmitted through the tissue is normalized by the excitation signal transmitted through the tissue, and so many of the fluorescence tomography systems do not require the use of time-resolved or frequency domain data, although research is still ongoing in this area. Since the applications of fluorescent molecules in humans are fairly limited, most of the work in fluorescence tomography has been in the realm of pre-clinical cancer research. Both commercial systems and academic research have been shown to be effective in tracking tumor protein expression and production, and tracking response to therapies.
Optical tomography found its application in industry as a sensor of thickness and internal structure of semiconductors .
See also
- Optical coherence tomographyOptical coherence tomographyOptical coherence tomography is an optical signal acquisition and processing method. It captures micrometer-resolution, three-dimensional images from within optical scattering media . Optical coherence tomography is an interferometric technique, typically employing near-infrared light...
- Diffuse optical imaging
- Computed tomography laser mammographyComputed Tomography Laser MammographyComputed Tomography Laser Mammography is the trademark of Imaging Diagnostic Systems, Inc. for its optical tomographic technique for female breast imaging....