We investigated the kinetics of a bolus intravenous administrated normal saline by using near-infrared diffuse optical
technique, and compared it with the kinetics of a non-targeted contrast agent indocyanine green (ICG) on small animal
tumor model. Two-compartment model was used to fit the dynamic curves at early stage, which considered saline and
ICG as either a negative or positive contrast agent. The purposes of the designed experiment reported here are to (1)
study the effect of saline administration on optical pharmacokinetics; (2) investigate the possibility of using normal
saline as contrast agent for the study of tumor pathophysiology. The study indicates that saline has different contrast
mechanism as ICG, and saline can provide enough optical contrast for the tumor kinetic study.
We developed a hybrid continuous-wave/frequency-domain instrument to obtain both spatial and spectral information of
the female breast. The two-dimensional (2D) tandem planar scanning of a compressed breast enables a pixel size of 2×2 mm2 and a continuous spectra acquisition from 650 nm to 900 nm at every image pixel with a 0.5 nm spectral step. A
2D spline interpolation algorithm is implemented to increase the data sampling rate and reduce the pixel size to 0.5×0.5 mm2. We then apply an edge-correction method to compensate the signal change due to the breast thickness
variation. The resulted optical density image is further processed using a previously developed second-derivative
algorithm to enhance the contrast and improve the spatial resolution of the optical inhomogeneities within the breast
tissue. The finer structures displayed in the second-derivative image offer better identification of the pixels of interest
associated with significant hemoglobin presence. We then employ a novel paired-wavelength oximetry method to
determine the absolution value of oxygen saturation for those identified pixels of interest. We found the majority of
oxygen saturation values from two healthy human subjects fall within the range 60%-95%, which is consistent with
previously published results. Breast oximetry could have a potential applicability toward breast cancer detection and
diagnostics and this novel paired-wavelength method can be a robust and accurate way to retrieve the oxygenation
information in vivo.
We present an experimental test of a new spectral approach that is aimed at quantifying the relative concentrations of two chromophores that are contained in a defect embedded in a turbid medium. The basic steps of our spectral approach are (a) perform a linear tandem scan of the source and detector across the defect; (b) measure the spectral dependence of the maximum change induced by the defect in the scanned intensity; (c) identify a set of appropriate pairs of wavelengths (1, 2) at which such maximum intensity changes are the same; and (d) measure the reduced scattering coefficient spectrum of the background medium. For each wavelength pair (1, 2), we obtain a measurement of the relative concentrations of the two chromophores, where the only required parameters are the extinction coefficients of the two chromophores and the ratio of the background scattering coefficients at 1 and 2. In a mixture of two test chromophores (blue food coloring dye and black India ink) contained in a 0.78-cm diameter cylinder, our spectral approach yielded relative concentrations values that were within 6% of their actual values. Although our paired-wavelength spectral approach is not generally applicable to any pair of chromophores, it is suitable for oxyhemoglobin and deoxyhemoglobin and is thus appropriate for oximetry of localized lesions in biological tissues.
We describe a Monte Carlo test of a new method for the calculation of the relative concentrations of two
localized absorbers in a highly scattering medium. The method, previously proposed by us, is based on a
property of the intensity changes caused by the localized absorbers, which is strictly verified by diffusion
theory within first order perturbation, and remains approximately verified beyond the limits of first order
perturbation. The applicability of the method was theoretically and experimentally validated in an infinite
medium geometry for "small size" perturbations, as well as for larger perturbations. The purpose of the
Monte Carlo test reported here is to show that the method is applicable also to a slab geometry for a
relatively large (both in size and optical contrast) perturbation. This test indicates that the dual wavelength
approach to the estimation of the relative concentration of two absorbers can be insensitive to the medium
geometry as well as the size and geometry of the localized inclusion.
We present a multisource, multidetector phased-array approach to diffuse optical imaging that is based on postprocessing continuous-wave data. We previously showed that this approach enhances the spatial resolution of diffuse optical imaging. We now demonstrate the depth discrimination capabilities of this approach and its potential to perform tomographic sectioning of turbid media. The depth discrimination results from the dependence of the sensitivity function on the depth coordinate z. To demonstrate the potential of this approach, we perform an experimental study of a turbid medium containing cylindrical inhomogeneities that are placed 2.0, 3.0, and 4.0 cm from a seven-element, 2-D source array. A single detector element is placed at a distance of 6.0 cm from the source array, and the measurement is repeated after switching the positions of the detector and the source array to simulate the case where both sources and detectors consist of a 2-D array of elements. We find that the proposed phased-array method is able to separate cylinders at different depths, thus showing cross-sectioning capabilities.
A three-element phased array approach based on post processing of continuous wave data for enhancing the spatial resolution of highly scattering media is presented. The method is based on the scanning of a three sources -one detector array along the system under investigation. The sources are turned on and offin a sequential mode in order to avoid cross talk among them. At each position of the sources-detector system along the medium intensity data are collected from the sources, multiplied by amplitude and phase factors, and combined in a phased-array algorithm. Optimal choices of the amplitude and phase factors are discussed. Experimental and theoretical evidence of the improved spatial resolution obtained with this method is provided.
We present a phased-array approach to diffuse optical imaging that is based on collecting continuous wave (CW) data using multiple sources and/or multiple detectors. The optical signals corresponding to individual source-detector pairs are combined by post processing after assigning individual amplitude and phase factors. Here, we demonstrate the enhancement in spatial resolution and the depth discrimination afforded by three-element linear phased arrays, either as stand alone units or in a 2-D crossed configuration. In this particular example, the (amplitude, phase) factors associated with the three array elements are (1,0), (2,π), (1,0), respectively. Experimental results on tissue like phantoms demonstrate the potential of the proposed source/detector arrays to enhance the performance of diffuse optical imaging.
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