Absorption Coefficient Measurements of Strongly Scattering Media Using Time-Resolved Transmittance of a Short Pulse in Near-Infrared (NIR) Wavelength Range

Abstract

Absorption coel~cient measurements of strongly scattering and weakly absorbing media have been performed using time resolved transmittance of a 100 fs pulse through a 30 mm slab containing latex spheres suspended in water and absorbing ink solutions. The scattering and absorption coefficients were selected so that the optical properties of the media were similar to those of biological tissues. Measured curves of time-resolved transmittance of the pulse through the media were used to estimate the optical properties of the media. The experiment was made at two different wavelengths, 784 nm and 810 nm. Estimated absorption coefficients were in gcod agreement with those measured in a nonscattering case by a spectrophotometer.

Early- and late-arriving photons in diffuse optical tomography/Früh und spät ankommende Photonen in der diffusen optischen Tomographie

“…The particle concentration was adjusted in such a way that the reduced scattering coefficient is similar to that of biological tissue. For modeling the absorbing inhomogeneity, Indian ink, with known spectral properties [14] , was added to material in a smaller cylinder in order to increase the absorption coefficient ( Figure 6 ). The diameter and the height of the cylinder were both 70 mm.…”

Time-resolved optical tomography using short-pulse laser for tumor detection

“…36,56,57 Moreover, validation of experimental measurements for tissue phantoms containing inhomogeneities reported in the literature has been performed using a diffusion-based model. 16,34,58 Authors of this group have validated the experimental measurements of transmitted signals for tissue phantoms with inhomogeneities embedded in them with solutions of the RTE obtained using DOM. 40 More studies are necessary for the validation of the forward model of the RTE with experimental measurements for the determination of tissue optical properties.…”

“…12 The potential of optical tomography as a new diagnostic tool has stimulated considerable interest since the past decade. [13][14][15][16][17][18][19] Although limited to about the first 5 cm of the body, the technique offers several advantages often not available in established imaging modalities such as ultrasound, x-ray computed tomography, and magnetic resonance imaging (MRI). [20][21][22] Two basic measurement methodologies are used for imaging: (i) frequency-domain methods that employ harmonically modulated photon density waves and phase-resolved detection, which measure the phase shift of the photon density waves and (ii) timedomain methods that use pulsed excitation and ultrafast detectors to examine the response of tissue to a short pulse of incident light.…”

“…Short-pulse laser probing techniques for diagnostics have distinct advantages over very large pulse width or continuous wave lasers primarily due to the additional information conveyed by the temporal distribution of the observed signal. 15,16,27,28 The distinct feature is the multiple-scattering-induced temporal distributions, which persists for a time period greater than the duration of the source pulse and is a function of the source pulse width as well as the optical properties of the medium. If the detection is carried out at the same short time scale (comparable to the order of the pulse width), the signal continues to be observed even for long times after the pulse has been off due to the time taken for the photons to migrate to the detector after multiple scattering in the media.…”

“…34 To overcome the scarcity of photons in time-gating, time-resolved measurements that use a diffuse component of the photons for image reconstruction have been used by many groups. 15,16,31,[35][36][37][38][39][40] Time-resolved techniques improve the localization and characterization of the inhomogeneities as information on the path length of each photon becomes available. Inhomogeneities differing from the surrounding tissue in terms of optical properties have a different influence on the distribution of the times of flight of photons.…”