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.
Famous quotes containing the word optical:
“It is said that a carpenter building a summer hotel here ... declared that one very clear day he picked out a ship coming into Portland Harbor and could distinctly see that its cargo was West Indian rum. A county historian avers that it was probably an optical delusion, the result of looking so often through a glass in common use in those days.”
—For the State of New Hampshire, U.S. public relief program (1935-1943)