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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 2D imaging methods are classified as diffuse optical imaging. 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 and may additionally measure redox states of cytochromes. The technique may also be referred to as diffuse optical tomography (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 fNIRS. Physical mechanism Biological tissues can be considered strongly diffusive med ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffuse Optical Tomography - Fiber-optic Array - Journal
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. It is possible to diffuse "uphill" from a region of lower concentration to a region of higher concentration, as in spinodal decomposition. Diffusion is a stochastic process due to the inherent randomness of the diffusing entity and can be used to model many real-life stochastic scenarios. Therefore, diffusion and the corresponding mathematical models are used in several fields beyond physics, such as statistics, probability theory, information theory, neural networks, finance, and marketing. The concept of diffusion is widely used in many fields, including physics ( particle diffusion), chemistry, biology, sociology, economics, statistics, data science, and finance (diffusion of people, ideas, data and price values). The central ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiative Transfer Equation And Diffusion Theory For Photon Transport In Biological Tissue
Photon transport in biological tissue can be equivalently modeled numerically with Photon transport monte carlo, Monte Carlo simulations or analytically by the radiative transfer equation (RTE). However, the RTE is difficult to solve without introducing approximations. A common approximation summarized here is the diffusion approximation. Overall, solutions to the diffusion equation for photon transport are more computationally efficient, but less accurate than Monte Carlo simulations. Definitions The RTE can mathematically model the transfer of energy as photons move inside a tissue. The flow of radiation energy through a small area element in the radiation field can be characterized by radiance L(\vec,\hat,t) with units \frac. Radiance is defined as energy flow per unit normal area per unit solid angle per unit time. Here, \vec denotes position, \hat denotes unit direction vector and t denotes time (Figure 1). Several other important physical quantities are based on the defini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Imaging
Medical optical imaging is the use of light as an investigational imaging technique for medical applications, pioneered by American Physical Chemist Britton Chance. Examples include optical microscopy, spectroscopy, endoscopy, scanning laser ophthalmoscopy, laser Doppler imaging, optical coherence tomography, and transdermal optical imaging. Because light is an electromagnetic wave, similar phenomena occur in X-rays, microwaves, and radio waves. 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 (DOI) is a method of imaging using near-infrared spectroscopy (NIRS) or fluorescence-based methods. When used to create 3D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffuse Optical Mammography
Diffuse optical mammography, or simply optical mammography, is an emerging imaging technique that enables the investigation of the breast composition through spectral analysis. It combines in a single non-invasive tool the capability to implement breast cancer risk assessment, lesion characterization, therapy monitoring and prediction of therapy outcome. It is an application of diffuse optics, which studies light propagation in strongly diffusive media, such as biological tissues, working in the red and near-infrared spectral range, between 600 and 1100 nm. Comparison with conventional imaging techniques Currently, the most common breast imaging techniques are X-ray mammography, ultrasounds, MRI and PET. X-ray mammography is widely spread for breast screening, thanks to its high spatial resolution and the short measurement time. However, it is not sensitive to the breast physiology, it is characterized by a limited efficiency in investigating dense breasts and it is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computed Tomography Laser Mammography
Computed tomography laser mammography (CTLM) is the trademark of Imaging Diagnostic Systems, Inc. (IDSI, United States) for its Optical tomography, optical tomographic technique for female breast imaging. This medical imaging technique uses laser energy in the near-infrared region of the spectrum to detect angiogenesis in the breast tissue. It is optical molecular imaging for hemoglobin, both oxygenated and deoxygenated. The technology uses laser in the same way computed tomography uses X-rays; the beams travel through tissue and suffer attenuation. A laser detector measures the intensity drop and the data is collected as the laser detector moves across the breast creating a tomography image. CTLM images show hemoglobin distribution in a tissue and can detect areas of angiogenesis surrounding malignant tumors, that stimulate this angiogenesis to obtain nutrients for growth. History Breast cancer affects 1 in 8 women, and an estimated 27% of people live at least 5 years after b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 research. Optical tomography in industry is used as a sensor of thickness and internal structure of semiconductors. Principle Optical tomography relies on the object under study being at least partially light-transmitting or translucent, so it works best on soft tissue, such as breast and brain tissue. 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. Types Diffuse optical tom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time-domain Diffuse Optics
Time-domain diffuse optics or time-resolved functional near-infrared spectroscopy is a branch of functional near-Infrared spectroscopy which deals with light propagation in diffusive media. There are three main approaches to diffuse optics namely continuous wave (CW), frequency domain (FD) and time-domain (TD). Biological tissue in the range of red to near-infrared wavelengths are transparent to light and can be used to probe deep layers of the tissue thus enabling various in vivo applications and clinical trials. Physical concepts In this approach, a narrow pulse of light (20 MHz) and finally, sufficient laser power (>1 mW) to achieve good signal to noise ratio. In the past bulky tunable Ti:sapphire Lasers were used. They provided a wide wavelength range of 400 nm, a narrow FWHM (< 1 ps) high average power (up to 1W) and high repetition (up to 100 MHz) frequency. However, they are bulky, expensive and take a long time for wavelength swapping. In recent years, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromophores
A chromophore is the part of a molecule responsible for its color. The word is derived . The color that is seen by our eyes is that of the light not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum (or in informal contexts, the spectrum under scrutiny). Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change in the molecule when hit by light. Conjugated pi-bond system chromophores Just like how two adjacent p-orbitals in a molecule will form a pi-bond, three or more adjacent p-orbitals in a molecule can form a conjugated pi-system. In a conjugated pi-system, electrons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-infrared Window In Biological Tissue
The near-infrared (NIR) window (also known as optical window or therapeutic window) defines the range of wavelengths from 650 to 1350 nanometre (nm) where light has its maximum depth of penetration in tissue. Within the NIR window, scattering is the most dominant light-tissue interaction, and therefore the propagating light becomes diffused rapidly. Since scattering increases the distance travelled by photons within tissue, the probability of photon absorption also increases. Because scattering has weak dependence on wavelength, the NIR window is primarily limited by the light absorption of blood at short wavelengths and water at long wavelengths. The technique using this window is called NIRS. Medical imaging techniques such as fluorescence image-guided surgery often make use of the NIR window to detect deep structures. Absorption properties of tissue components The absorption coefficient (\mu_) is defined as the probability of photon absorption in tissue per unit path length. D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 including blood sugar, pulse oximetry, functional neuroimaging, sports medicine, elite sports training, ergonomics, rehabilitation, neonatal research, brain computer interface, urology (bladder contraction), and neurology (neurovascular coupling). There are also applications in other areas as well such as pharmaceutical, food and agrochemical quality control, atmospheric chemistry, combustion propagation. Theory Near-infrared spectroscopy is based on molecular overtone and combination vibrations. Overtones and combinations exhibit lower intensity compared to the fundamental, as a result, the molar absorptivity in the near-IR region is typically quite small. (NIR absorption bands are typically 10–100 times weaker than the corresponding fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Absorption (electromagnetic Radiation)
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy—and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). A notable effect of the absorption of electromagnetic radiation is attenuation of the radiation; attenuation is the gradual reduction of the intensity of light waves as they propagate through a medium. Although the absorption of waves does not usually depend on their intensity (linear absorption), in certain conditions (optics) the medium's transparency changes by a factor that varies as a function of wave intensity, and saturable absorption (or nonlinear absorption) occurs. Quantifying absorption Many approaches can potentially quantify radiation absorption, with key examples following. * The absorption coefficient along with some closely related derived quantities * The attenuation coefficient (NB used infrequently with meaning ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 radiation) in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections of radiation that undergo scattering are often called ''diffuse reflections'' and unscattered reflections are called ''specular'' (mirror-like) reflections. Originally, the term was confined to light scattering (going back at least as far as Isaac Newton in the 17th century). As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that William Herschel could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800. John Tyndall, a pioneer in light scattering research, noted the connecti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
