The optical coefficients (μs, μa, μ's and g)of human cancerous and normal prostate tissues were investigated and
compared in the spectral range of 750nm - 860 nm. The fractal dimensional parameters including fractal dimension (Df),
cutoff diameter (dmax) and the most efficient diameter (dm) between the cancerous and normal prostate tissues were
determined based on the extinction and diffusion reflection intensity measurements and the determination ofμs, μa, μ's and g. The results are in good agreement with prostate cancer evolution defined by Gleason Grades. The difference of fractal dimensional parameters and optic
Optical imaging using independent component analysis (OPTICA) and time reversal optical tomography (TROT)
approaches are used to detect, locate, and obtain cross-section images of two tumor pieces inside a model human breast
assembled using ex vivo human breast tissues and configured as a semi-cylindrical slab of uniform thickness. The
experimental arrangement realized a multi-source probing scheme to illuminate an end face (source plane) of the slab
sample using 750 nm, 800 nm and 830 nm beams of laser light. A multi-detector signal acquisition scheme measured
transmitted light intensity distribution on the other end face (detection plane). This combined multi-source probing and
multi-detector sensing approach culminated in multiple spatial and angular views of the sample necessary for target
localization. The perturbations in light intensity distribution in the detection plane were analyzed using both the OPTICA
and the TROT approaches to obtain locations of the tumor pieces. A back-projection technique with OPTICA provided
cross-section images and estimates of cross section of the targets within the sample. The estimated locations and
dimensions of targets are in good agreement with the results of a corroborating magnetic resonance imaging experiment
and known values.
Time reversal optical tomography (TROT) approach is used to detect and locate absorptive targets embedded in a highly
scattering turbid medium to assess its potential in breast cancer detection. TROT experimental arrangement uses multi-source
probing and multi-detector signal acquisition and Multiple-Signal-Classification (MUSIC) algorithm for target
location retrieval. Light transport from multiple sources through the intervening medium with embedded targets to the
detectors is represented by a response matrix constructed using experimental data. A TR matrix is formed by multiplying
the response matrix by its transpose. The eigenvectors with leading non-zero eigenvalues of the TR matrix correspond to
embedded objects.
The approach was used to: (a) obtain the location and spatial resolution of an absorptive target as a function of its
axial position between the source and detector planes; and (b) study variation in spatial resolution of two targets at the
same axial position but different lateral positions. The target(s) were glass sphere(s) of diameter ~9 mm filled with ink
(absorber) embedded in a 60 mm-thick slab of Intralipid-20% suspension in water with an absorption coefficient μa~
0.003 mm-1 and a transport mean free path lt~ 1 mm at 790 nm, which emulate the average values of those parameters
for human breast tissue. The spatial resolution and accuracy of target location depended on axial position, and target
contrast relative to the background. Both the targets could be resolved and located even when they were only 4-mm
apart. The TROT approach is fast, accurate, and has the potential to be useful in breast cancer detection and localization.
The absorption coefficient, the scattering coefficient and the anisotropy factor of a highly scattering medium are determined using the diffuse reflectance of an obliquely incident beam of circularly polarized light. This approach determines both the anisotropy factor and the cutoff size parameter for the fractal continuous scattering medium such as biological tissue and tissue phantoms from depolarization of the backscattered light.
Optical imaging using independent component analysis (OPTICA) is enhanced to provide a high resolution cross section
imaging of objects in a turbid medium by a backprojection technique. The performance is demonstrated by imaging a
human breast model made of ex vivo human breast tissues. Cancerous site of 5mm size is detected at the midplane of the
33mm thick breast model. The reconstructed cross section image compares favorably with pathology findings.
The interaction of light with tissue and cells is the underlying mechanism for optical biomedical imaging and spectroscopy to detect pathology changes. We use fractal continuous random media to model visible and near infrared light scattering by biological tissue and cell suspensions, which provides a simple relation between the morphological features of the sample and its optical properties (absorption, scattering and anisotropic factor of light scattering). Good agreement with experimental results are found for this fractal continuous random medium model. A novel optical biopsy scheme of oblique incidence Fourier reflectometry is proposed for spectroscopic tissue diagnosis based on the model.
An innovative approach for three-dimensional localization and characterization of a fluorescent target embedded in a turbid medium is presented. The target was a ~4-mm diameter glass sphere with a solution of indocyanine green placed within a 50-mm thick tissuelike phantom with mean free path of ~1-mm at 784-nm and a ~ 26-mm thick ex vivo breast tissue slab. The experimental approach uses a multi-source illumination, and a multi-detector signal acquisition scheme. An analysis scheme based on the independent component analysis from information theory is used for target localization and characterization. Independent component analysis of the perturbation in the spatial intensity distribution of the fluorescent signal measured on the exit plane of the turbid medium locates the embedded objects. The location and size, of the embedded objects are obtained from a Green's function analysis and back-projection Fourier transform of the retrieved independent components.
A new imaging approach for 3-D localization and characterization of objects in a turbid medium using independent component analysis (ICA) from information theory is developed and demonstrated using simulated data. This approach uses a multisource and multidetector signal acquisition scheme. ICA of the perturbations in the spatial intensity distribution measured on the medium boundary sorts out the embedded objects. The locations and optical characteristics of the embedded objects are obtained from a Green's function analysis based on any appropriate model for light propagation in the background medium. This approach is shown to locate and characterize absorptive and scattering inhomogeneities within highly scattering medium to a high degree of accuracy. In particular, we show this approach can discriminate between absorptive and scattering inhomogeneities, and can locate and characterize complex inhomogeneities, which are both absorptive and scattering. The influence of noise and uncertainty in background absorption or scattering on the performance of this approach is investigated.
A new imaging approach for three-dimensional localization and characterization of absorptive, scattering or fluorescent objects in a turbid medium is presented and demonstrated using simulated and
experimental data. This approach uses a multi-source and multi-detector signal acquisition scheme and independent component analysis (ICA) from information theory for target localization and characterization. Independent component analysis of the perturbation in the spatial intensity distribution or the fluorescent signal measured on the medium boundary sorts out the embedded objects. The location and optical characteristics (size, shape and optical property) of the embedded objects are obtained from a Green's
function analysis based on an appropriate model for light propagation in the background medium and back-projections of the retrieved independent components.
A new approach for optical fluorescence tomographic imaging of targets in a turbid medium that uses the independent component analysis (ICA) from information theory is presented. Fluorescence signals from targets embedded in a turbid medium are measured on the boundary of the medium using a multi-source excitation and a multi-detector acquisition scheme. Differences between excitation and fluorescence wavelengths enable sensitive, minimal-background signal acquisition. ICA of the fluorescence signal on the medium boundary sorts out the embedded ob-jects, and their locations are obtained from Green’s function analysis based on any appropriate light propagation model. Fluorescence tomographic imaging experiments were carried out using Intralipid-10% suspension in water contained in a 50-mm thick rectangular transparent plastic cell as the turbid medium, and small glass spheres containing indocyanine green (ICG) solution as fluorescent targets. The near-infrared (NIR) fluorescence was excited using 785 nm light, and monitored over a narrow band around 830 nm. The transport mean free paths at 785 nm and 830 nm were 1.01 mm and 1.14 mm, respectively. The approach could image and determine the position of an ICG filled sphere of radius as small as 4 mm. It is applicable to small objects, different medium geometries, and amenable to near real time imaging applications.
A new algorithm based on multi-static data and vector subspace classification to eigenvectors of a round-trip matrix is introduced for optical imaging and localization of objects embedded in a turbid medium. The transport of light from multiple sources through excitation of the embedded objects to the array of detectors is represented by a response matrix that can be constructed from experimental data. The 'round-trip (RT) matrix’ is constructed by multiplying the response matrix by its transpose for continuous-wave (adjoint matrix for frequency domain) illumination. Mathematically, the RT matrix is equivalent to transfer of light from the sources via the embedded objects to the array of detectors and back, and is similar to the time-reversal matrix used in the general area of array processing for acoustic and radar time-reversal imaging. The eigenvectors with leading non-zero eigenvalues of the RT matrix correspond to embedded objects, which are orthogonal to the vectors in the noise subspace. The vector subspace method along with Green’s functions calculated from an appropriate model for light propagation through turbid media is then used to determine the locations of the embedded objects. We tested this algorithm in simulation for light transmitting through a 50 l tr thick (l tr ~ 1 mm is transport mean free path) parallel slab turbid medium with up to six embedded absorptive objects. The method was able to globally locate all six objects with surprising accuracy. This “round-trip tomographic imaging” approach is fast, applicable to different geometries and to different forward models.
Time-sliced and quasi continuous wave two-dimensional (2-D)transillumination imaging methods were used with independent component analysis (ICA) to generate three-dimensional (3-D)tomographic maps of absorbing and scattering inhomogeneities embedded in tissue-like turbid media. The thickness of the turbid media in both the cases was approximately 50 times the transport mean free path. The experimental arrangement for time-sliced optical imaging used 150-fs, 1 kHz repetition-rate, 800-nm light pulses from a Ti:sapphire laser system for sample illumination, and an ultrafast gated intensified camera system (UGICS) providing a minimal gate duration of 80 ps for recording 2-D images. Quasi continuous wave (CW) imaging used 784-nm CW output of a diode laser as the light source and a cooled charge coupled device (CCD) camera for recording 2-D images. Translation stages were used to scan the samples over an array of points in the x-y plane. The temporal profile of the transmitted pulse was used to extract the average optical properties of the media. An independent component separation of the signal, in conjunction with diffusive photon migration theory was used to locate the embedded inhomogeneities. An improved lateral and axial localization of the inhomogeneity over the result obtained by common photon migration reconstruction algorithm is achieved.
Spectroscopic and time-sliced two-dimensional (2-D) transillumination imaging methods were used to investigate ex vivo tumor and normal tissues of human breast and parotid gland. The experimental arrangement for time-sliced optical imaging uses 120-fs, 1 kHz repetition-rate, 800-nm light pulses from a Ti:sapphire laser system for sample illumination and a charge coupled device (CCD) camera coupled to a gated image intensifier for recording 2-D images. The spectroscopic imaging arrangement uses 1210-1325 nm tunable output of a Cr: forsterite laser for sample illumination, a Fourier space gate to discriminate against multiple-scattered light, and a near-infrared (NIR) area camera to record 2-D images. Images recorded with earlier temporal slices of transmitted light highlighted tumors, while those recorded with later slices accentuated normal tissues. When light was tuned closer to the 1203 nm absorption resonance of adipose tissues, a marked enhancement in contrast between the images of adipose and fibrous tissues was observed. A similar wavelength-dependent difference between normal and cancerous tissues was observed. These results correlate well with pathology and nuclear magnetic resonance based analyses of the samples. This work demonstrates the advantages of time-resolved spectroscopic approach for imaging tumors in body organs.
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