Optical imaging
Encyclopedia
Optical imaging is an imaging technique.
Optics
usually describes the behavior of visible, ultraviolet, and infrared light used in imaging.
Because light is an electromagnetic wave, similar phenomena occur in X-rays, microwaves, radio waves. Chemical imaging
or molecular imaging
involves inference from the deflection of light
emitted from (e.g. laser
, infrared
) source to structure
, texture, anatomic
and chemical properties of material (e.g. crystal
, cell tissue). Optical imaging systems may be divided into diffusive and ballistic imaging systems.
or NIROT) is a technique that gives neuroscientist
s the ability to simultaneously obtain information about the source of neural activity as well as its time course. In other words, it allows them to "see" neural activity and study the functioning of the brain
.
In this method, a near-infrared laser is positioned on the scalp
. Detectors composed of optical fiber
bundles are located a few centimeters away from the light source. These detectors sense how the path of light is altered, either through absorption
or scattering
, as it traverses brain tissue.
This method can provide two types of information. First, it can be used to measure the absorption of light, which is related to concentration of chemicals in the brain. Second, it can measure the scattering of light, which is related to physiological characteristics such as the swelling of glia and neuron
s that are associated with neuronal firing.
Typical applications include rapid 2D optical topographic imaging of the event-related optical signal
(EROS) or Near infrared spectroscopy
(NIRS) signal following brain
activity and tomographic
reconstruction
of an entire 3D volume of tissue to diagnose breast cancer
or neonatal brain
haemorrhage. The spatial resolution of Diffuse Optical Tomography (DOT) techniques is several millimeters, comparable to the lower end of functional magnetic resonance imaging
(fMRI). The temporal resolution of EROS is very good, comparable to electroencephalography
, and magnetoencephalography
(~milliseconds), while that of NIRS, which measures hemodynamic changes rather than neuronal activity, is comparable to fMRI (~seconds). DOT instruments are relatively low cost ($150,000), portable and immune to electrical interference. The signal-to-noise ratio of NIRS is quite good, enabling detection of responses to single events in many cases. EROS signals are much weaker, typically requiring averaging of many responses.
Important chemicals that this method can detect include hemoglobin
and cytochrome
s.
s to create high-resolution (near diffraction limited) images through scattering media.
Optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
usually describes the behavior of visible, ultraviolet, and infrared light used in imaging.
Because light is an electromagnetic wave, similar phenomena occur in X-rays, microwaves, radio waves. Chemical imaging
Chemical imaging
Chemical imaging is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time informations....
or molecular imaging
Molecular imaging
Molecular imaging originated from the field of radiopharmacology due to the need to better understand the fundamental molecular pathways inside organisms in a noninvasive manner.- Overview :...
involves inference from the deflection of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
emitted from (e.g. laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
, 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...
) source to structure
Structure
Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...
, texture, anatomic
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
and chemical properties of material (e.g. crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
, cell tissue). Optical imaging systems may be divided into diffusive and ballistic imaging systems.
Diffusive optical imaging in neuroscience
Diffusive optical imaging (also known as Near Infrared Optical tomographyOptical tomography
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...
or NIROT) is a technique that gives neuroscientist
Neuroscientist
A neuroscientist is an individual who studies the scientific field of neuroscience or any of its related sub-fields...
s the ability to simultaneously obtain information about the source of neural activity as well as its time course. In other words, it allows them to "see" neural activity and study the functioning of the 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,...
.
In this method, a near-infrared laser is positioned on the scalp
Scalp
The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.-Layers:It is usually described as having five layers, which can conveniently be remembered as a mnemonic:...
. Detectors composed of optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
bundles are located a few centimeters away from the light source. These detectors sense how the path of light is altered, either through absorption
Absorption (electromagnetic radiation)
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
or scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
, as it traverses brain tissue.
This method can provide two types of information. First, it can be used to measure the absorption of light, which is related to concentration of chemicals in the brain. Second, it can measure the scattering of light, which is related to physiological characteristics such as the swelling of glia and neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s that are associated with neuronal firing.
Typical applications include rapid 2D optical topographic imaging of the event-related optical signal
Event-related optical signal
Event-related optical signal is a brain-scanning technique which uses infrared light through optical fibers to measure changes in optical properties of active areas of the cerebral cortex...
(EROS) or Near infrared spectroscopy
Near infrared spectroscopy
Near-infrared spectroscopy is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum...
(NIRS) signal following brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
activity and tomographic
Tomography
Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science,...
reconstruction
Reconstruction algorithm
In tomography, a variety of practical reconstruction algorithms have been developed to implement the process of reconstruction of a 3-dimensional object from its projections...
of an entire 3D volume of tissue to diagnose breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
or neonatal brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
haemorrhage. The spatial resolution of Diffuse Optical Tomography (DOT) techniques is several millimeters, comparable to the lower end of functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI). The temporal resolution of EROS is very good, comparable to electroencephalography
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
, and magnetoencephalography
Magnetoencephalography
Magnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
(~milliseconds), while that of NIRS, which measures hemodynamic changes rather than neuronal activity, is comparable to fMRI (~seconds). DOT instruments are relatively low cost ($150,000), portable and immune to electrical interference. The signal-to-noise ratio of NIRS is quite good, enabling detection of responses to single events in many cases. EROS signals are much weaker, typically requiring averaging of many responses.
Important chemicals that this method can detect include hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
and cytochrome
Cytochrome
Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....
s.
Ballistic optical imaging
Ballistic optical imaging systems ignore the diffused photons and rely only on the ballistic photonBallistic photon
Ballistic photons are the light photons that travel through a scattering medium in a straight line. Also known as ballistic light. If laser pulses are sent through a turbid medium such as fog or body tissue, most of the photons are either randomly scattered or absorbed. However, across short...
s to create high-resolution (near diffraction limited) images through scattering media.
External links
- Understanding Near-Infrared Imaging – Resource to better understand the benefits of Near-Infrared imaging.
- Diffuse Optics Lab at University of Pennsylvania, Philadelphia
- DOI at Massachusetts General Hospital, Boston
- Biomedical Imaging Group at Dartmouth
- DOS/I Lab at the Beckman Laser Institute, University of California, Irvine
- A review article in the field by A.P. Gibson et al.
- An article on optical breast imaging
- Illinois ECE 460 Principles of Optical Imaging Course lecture notes