Medical optical imaging is the use of

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

as an investigational

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

technique for

medical Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

applications, pioneered by American

Physical Chemist Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mecha ...

Britton Chance Britton "Brit" Chance (July 24, 1913 – November 16, 2010) was an American biochemist, biophysicist, scholar, and inventor whose work helped develop spectroscopy as a way to diagnose medical problems. He was "a world leader in transforming ...

. Examples include

optical microscopy Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

endoscopy An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are insert ...

, scanning laser ophthalmoscopy,

laser Doppler imaging Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to image live tissue. When the laser light reaches the tissue, the moving blood cells generate Doppler components in the reflected ( backscattered) light. The light that comes ...

optical coherence tomography Optical coherence tomography (OCT) is a high-resolution imaging technique with most of its applications in medicine and biology. OCT uses coherent near-infrared light to obtain micrometer-level depth resolved images of biological tissue or oth ...

, and

transdermal optical imaging Transdermal optical imaging, also known as transdermal optical imagery or TOI, is a method of detecting blood flow of the face by measuring hemoglobin concentration using a digital video camera. Because of the translucent property of skin, light ca ...

. Because light is an

electromagnetic wave In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ...

, similar phenomena occur in

X-rays An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

microwaves Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz an ...

, and

radio waves Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths ...

. Optical imaging systems may be divided into diffusive and ballistic imaging systems. A model for photon migration in turbid biological media has been developed by Bonner et al. Such a model can be applied for interpretation data obtained from laser Doppler blood-flow monitors and for designing protocols for therapeutic excitation of tissue chromophores.

Diffusive optical imaging

Diffuse optical imaging Diffuse optical imaging (DOI) is a method of imaging using near-infrared spectroscopy (NIRS) or fluorescence-based methods. When used to create 3D volumetric models of the imaged material DOI is referred to as diffuse optical tomography, whereas ...

(DOI) is a method of imaging using

near-infrared spectroscopy Near-infrared spectroscopy (NIRS) is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (from 780 nm to 2500 nm). Typical applications include medical and physiological diagnostics and research inc ...

(NIRS) or fluorescence-based methods. When used to create 3D volumetric models of the imaged material DOI is referred to as diffuse optical tomography, whereas 2D imaging methods are classified as diffuse optical topography. The technique has many applications to neuroscience, sports medicine, wound monitoring, and cancer detection. Typically DOI techniques monitor changes in concentrations of oxygenated and deoxygenated

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

and may additionally measure redox states of cytochromes. The technique may also be referred to as diffuse

optical 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. Optical tomography is used mostly in medical imaging re ...

(DOT), near infrared optical tomography (NIROT) or fluorescence diffuse optical tomography (FDOT), depending on the usage. In neuroscience, functional measurements made using NIR wavelengths, DOI techniques may classify as

functional near infrared spectroscopy Functional near-infrared spectroscopy (fNIRS) is an optical brain monitoring technique which uses near-infrared spectroscopy for the purpose of functional neuroimaging. Using fNIRS, brain activity is measured by using near-infrared light to estima ...

(fNIRS).

Ballistic optical imaging

Ballistic photon Ballistic light, also known as ballistic photons, is photons of light that have traveled through a scattering (turbid) medium in a straight line. When pulses of laser light pass through a turbid medium such as fog or body tissue, most of the pho ...

s are the

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

s that travel through a

scattering In physics, scattering is a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiat ...

(

turbid Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and wate ...

)

medium Medium may refer to: Aircraft *Medium bomber, a class of warplane * Tecma Medium, a French hang glider design Arts, entertainment, and media Films * ''The Medium'' (1921 film), a German silent film * ''The Medium'' (1951 film), a film vers ...

in a straight line. Also known as ballistic light. If

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

pulses are sent through a turbid medium such as

fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus and is heavily influenc ...

body tissue In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete org ...

, most of the photons are either randomly scattered or absorbed. However, across short distances, a few photons pass through the scattering medium in straight lines. These coherent photons are referred to as ballistic photons. Photons that are slightly scattered, retaining some degree of

coherence Coherence is, in general, a state or situation in which all the parts or ideas fit together well so that they form a united whole. More specifically, coherence, coherency, or coherent may refer to the following: Physics * Coherence (physics ...

, are referred to as ''snake'' photons. If efficiently detected, there are many applications for ballistic photons especially in coherent high resolution

medical imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to revea ...

systems. Ballistic scanners (using ultrafast time gates) and

(OCT) (using the

interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

principle) are just two of the popular imaging systems that rely on ballistic photon detection to create

diffraction-limited In optics, any optical instrument or systema microscope, telescope, or camerahas a principal limit to its resolution due to the physics of diffraction. An optical instrument is said to be diffraction-limited if it has reached this limit of res ...

images. Advantages over other existing imaging modalities (e.g.,

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

and

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

) is that ballistic imaging can achieve a higher resolution in the order of 1 to 10 micro-meters, however it has limited imaging depth. Furthermore, more scattered 'quasi-ballistic' photons are often measured as well to increase the signal 'strength' (i.e.,

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

). Due to the exponential reduction (with respect to distance) of ballistic photons in a scattering medium, often

image processing An image or picture is a visual representation. An image can be two-dimensional, such as a drawing, painting, or photograph, or three-dimensional, such as a carving or sculpture. Images may be displayed through other media, including a pr ...

techniques are applied to the raw captured ballistic images, to reconstruct high quality ones. Ballistic imaging modalities aim to reject non-ballistic photons and retain ballistic photons that carry useful information. To perform this task, specific characteristics of ballistic photons vs. non-ballistic photons are used, such as ''

time of flight Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...

'' through coherence gated imaging, collimation, wavefront propagation, and polarization.

References

External links

Medical Optics Group
at ICFO, Barcelona, Spain
Understanding Near-Infrared Imaging
– Resource to better understand the benefits of Near-Infrared imaging.
Diffuse Optics Lab at University of Pennsylvania, PhiladelphiaDOI at Massachusetts General Hospital, BostonDOS/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 imagingIllinois ECE 460 Principles of Optical Imaging
Course lecture notes *MRRA Inc. fNIRS System

{{Medical imaging Optical imaging, Neuroimaging

Diffusive optical imaging

Ballistic optical imaging

See also

References

External links