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A new approach for optical imaging and localization of objects in turbid media that makes use of the independent component analysis (ICA) from information theory is demonstrated. Experimental arrangement realizes a multisource illumination of a turbid medium with embedded objects and a multidetector acquisition of transmitted light on the medium boundary. The resulting spatial diversity and multiple angular observations provide robust data for three-dimensional localization and characterization of absorbing and scattering inhomogeneities embedded in a turbid medium. ICA of the perturbations in the spatial intensity distribution on the medium boundary sorts out the embedded objects, and their locations are obtained from Green's function analysis based on any appropriate light propagation model. Imaging experiments were carried out on two highly scattering samples of thickness approximately 50 times the transport mean-free path of the respective medium. One turbid medium had two embedded absorptive objects, and the other had four scattering objects. An independent component separation of the signal, in conjunction with diffusive photon migration theory, was used to locate the embedded inhomogeneities. In both cases, improved lateral and axial localizations of the objects over the result obtained by use of common photon migration reconstruction algorithms were achieved. The approach is applicable to different medium geometries, can be used with any suitable photon propagation model, and is amenable to near-real-time imaging applications. OCIS codes: 170.7050, 170.5280, 170.3660, 100.3190, 100.3010.

Transillumination images of objects hidden in normal and cancerous human breast tissues and bovine, porcine, and gallinaceous (chicken) tissues as well as model-random-scattering media were recorded with 1250-nm light from a chromium-doped forsterite laser. A Fourier space gate and a polarization gate were used to sort out image-bearing photons and discriminate against multiply scattered image-blurring photons. Better contrast, higher spatial resolution, and deeper penetration of samples were achieved for imaging with 1250-nm light than those obtained at shorter wavelengths, such as 1064 nm from a neodymium-doped yttrium aluminum garnet (YAG) laser. Better contrast and higher resolution were also obtained when the object was imaged through normal human breast tissue than through cancerous breast tissue. Images with marked distinction between fatty and fibrous human breast tissues were obtained when the Cr:forsterite laser was tuned to 1225 nm, a wavelength that resonates with an optical absorption band of breast fat tissues. Imaging with linearly polarized light revealed that the image quality depends significantly on the orientation of the polarization of the incident light with respect to the fibers in the bovine tissue.

Optical imaging and localization of objects inside a highly scattering medium, such as a tumor in the breast, is a challenging problem with many practical applications. Conventional imaging methods generally provide only two-dimensional (2-D) images of limited spatial resolution with little diagnostic ability. Here we present an inversion algorithm that uses time-resolved transillumination measurements in the form of a sequence of picosecond-duration intensity patterns of transmitted ultrashort light pulses to reconstruct three-dimensional (3-D) images of an absorbing object located inside a slab of a highly scattering medium. The experimental arrangement used a 3-mm-diameter collimated beam of 800-nm, 150-fs, 1-kHz repetition rate light pulses from a Ti:sapphire laser and amplifier system to illuminate one side of the slab sample. An ultrafast gated intensified camera system that provides a minimum FWHM gate width of 80 ps recorded the 2-D intensity patterns of the light transmitted through the opposite side of the slab. The gate position was varied in steps of 100 ps over a 5-ns range to obtain a sequence of 2-D transmitted light intensity patterns of both less-scattered and multiple-scattered light for image reconstruction. The inversion algorithm is based on the diffusion approximation of the radiative transfer theory for photon transport in a turbid medium. It uses a Green's function perturbative approach under the Rytov approximation and combines a 2-D matrix inversion with a one-dimensional Fourier-transform inversion to achieve speedy 3-D image reconstruction. In addition to the lateral position, the method provides information about the axial position of the object as well, whereas the 2-D reconstruction methods yield only lateral position.

Diffuse optical imaging (DOI) for detecting and locating targets in a highly scattering turbid medium is treated as a blind source separation (BSS) problem. Three matrix decomposition methods, independent component analysis (ICA), principal component analysis (PCA), and nonnegative matrix factorization (NMF) were used to study the DOI problem. The efficacy of resulting approaches was evaluated and compared using simulated and experimental data. Samples used in the experiments included Intralipid-10% or Intralipid-20% suspension in water as the medium with absorptive or scattering targets embedded. [ABSTRACT FROM AUTHOR]

Optical imaging using independent component analysis (OPTICA) has been used for detection, 3D localization, and cross-section imaging of a tumor inside a model human breast composed of ex vivo human breast tissues. OPTICA uses a multisource target illumination and multidetector signal acquisition scheme to obtain multiple spatial and angular views of the sample for target localization. Independent component analysis of the perturbations in the spatial light intensity distribution measured on the sample boundary sorts out the signal originating from individual targets. A back-projection technique estimates the cross-section of each target. The approach correctly provided the positions of a tumor located at the mid-plane and two glandular structures located at different positions within the 33-mm thick model breast. The reconstructed cross-section images are in good agreement with known dimensions of the structures, and pathological findings. [ABSTRACT FROM PUBLISHER]

Time-gated optical imaging of objects in turbid water was carried out in a backscattering geometry using light pulses of different pulse widths and a time-gated detection scheme with variable gate widths. Experimental results demonstrate that ultrashort pulsed illumination with ultrashort gated detection significantly improve image contrast as compared to any other combinations. These results are important for imaging objects embedded in turbid media, such as cloud, fog, smoke, murky water, and biological tissues for military, civilian, and medical applications. [ABSTRACT FROM AUTHOR]