Diffuse Optical Tomography - fiber-optic array - journal

Diffuse optical imaging (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 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 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

cytochrome Cytochromes are redox-active proteins containing a heme, with a central iron (Fe) atom at its core, as a cofactor. They are involved in the electron transport chain and redox catalysis. They are classified according to the type of heme and its ...

s. 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 fNIRS.

Physical mechanism

Biological tissues can be considered strongly diffusive media, since during light propagation the

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 ...

phenomenon is dominant over

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which su ...

in the so-called "therapeutic window" spectral range. Photon migration in diffusive media is described by the heuristic model of the

diffusion equation The diffusion equation is a parabolic partial differential equation. In physics, it describes the macroscopic behavior of many micro-particles in Brownian motion, resulting from the random movements and collisions of the particles (see Fick's l ...

, which offers analytical solutions for some specific geometries. Starting from the measured absorption and scattering coefficients, it is possible to derive the concentrations of tissues' main

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 chr ...

. Diffuse optical imaging can be implemented in

time domain In mathematics and signal processing, the time domain is a representation of how a signal, function, or data set varies with time. It is used for the analysis of mathematical functions, physical signals or time series of economic or environmental ...

, frequency domain or continuous wave, in reflectance or transmittance configuration.

Limitations and Advances in Diffuse Optical Tomography

Although diffuse optical tomography (DOT) enables greater imaging depth—on the order of several centimeters—compared to other optical imaging techniques, it suffers from key limitations, including relatively low spatial resolution and slow image acquisition and reconstruction times To overcome these limitations, a number of improvements have been proposed across the imaging pipeline. These include advances in acquisition strategies, signal processing techniques, and reconstruction algorithms.

Confocal Time-of-Flight Diffuse Optical Tomography

Conventional DOT suffers from image degradation due to the highly scattering nature of biological tissues, which leads to poor contrast and depth localization. Confocal Time-of-Flight Diffuse Optical Tomography (TOF-DOT) addresses this by using time-gated detection to selectively collect early-arriving photons that have taken more direct paths through tissue. This reduces the influence of multiply scattered photons and improves the signal-to-noise ratio. The TOF-DOT method thereby enhances image resolution and contrast, offering improved clarity in reconstructed images. Both simulations and experimental studies on tissue phantoms have demonstrated superior imaging performance compared to traditional DOT methods. However, this technique has yet to be validated in vivo.

References

{{reflist Medical imaging Optical imaging

Physical mechanism

Limitations and Advances in Diffuse Optical Tomography

Confocal Time-of-Flight Diffuse Optical Tomography

See also

References