Ultrafast time-gated imaging in thick tissues: a step toward optical mammography.
TL;DR: With an ultrafast time-gated optical detection method, a thin translucent strip of fat hidden inside a 4-cm-thick tissue is located with millimeter spatial resolution with high precision.
Abstract: With an ultrafast time-gated optical detection method, a thin translucent strip of fat (2.5 mm thick) hidden inside a 4-cm-thick tissue is located with millimeter spatial resolution.
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TL;DR: This review is an attempt to indicate which sets of phantoms are optimal for specific applications, and provide links to studies that characterize main phantom material properties and recipes.
Abstract: Optical spectroscopy, imaging, and therapy tissue phantoms must have the scattering and absorption properties that are characteristic of human tissues, and over the past few decades, many useful models have been created. In this work, an overview of their composition and properties is outlined, by separating matrix, scattering, and absorbing materials, and discussing the benefits and weaknesses in each category. Matrix materials typically are water, gelatin, agar, polyester or epoxy and polyurethane resin, room-temperature vulcanizing (RTV) silicone, or polyvinyl alcohol gels. The water and hydrogel materials provide a soft medium that is biologically and biochemically compatible with addition of organic molecules, and are optimal for scientific laboratory studies. Polyester, polyurethane, and silicone phantoms are essentially permanent matrix compositions that are suitable for routine calibration and testing of established systems. The most common three choices for scatters have been: (1.) lipid based emulsions, (2.) titanium or aluminum oxide powders, and (3.) polymer microspheres. The choice of absorbers varies widely from hemoglobin and cells for biological simulation, to molecular dyes and ink as less biological but more stable absorbers. This review is an attempt to indicate which sets of phantoms are optimal for specific applications, and provide links to studies that characterize main phantom material properties and recipes.
763Â citations
TL;DR: Information is presented on the design of the optical mammo system, the clinical measurements and the imaging results from an initial group of ten patients, and discussions about ongoing research on optical tomography.
Abstract: The results of the first set of clinical trials with the Philips optical mammography prototype system are summarized. This optical mammo prototype is designed to image the interior of the female breast with the help of near-infrared (NIR) laser light transmission measurements. This study is expected to lead to optical tomography systems for breast cancer detection. This paper presents information on the design of the optical mammo system, the clinical measurements and the imaging results from an initial group of ten patients, and discussions about ongoing research on optical tomography.
274Â citations
Cites background from "Ultrafast time-gated imaging in thi..."
...Time resolved transillumination with short laser pulses has been studied for the extraction of different tissue parameters [ 9 ]....
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TL;DR: In this paper, a finite-element reconstruction algorithm for optical data based on a diffusion equation approximation is presented and confirmed by a series of simulations and experiments using phantoms having optical properties in the range of those expected for tissues.
Abstract: Optical image reconstruction in a heterogeneous turbid medium with the use of frequency-domain measurements is investigated in detail. A finite-element reconstruction algorithm for optical data based on a diffusion equation approximation is presented and confirmed by a series of simulations and experiments using phantoms having optical properties in the range of those expected for tissues. Simultaneous reconstruction of absorption and scattering coefficients is achieved both theoretically and experimentally. Images with different target locations and contrast levels between target and background are also successfully recovered. All reconstructed images from both simulated and experimental data are derived directly from absolute optical data in which no differential measurement scheme is used. Results from the use of simulated and measured data suggest that quantitative images can be produced in terms of absorption and scattering coefficient values and location, size, and shape of heterogeneities within a circular background region over a range of contrast levels. Further, the effects of modulation frequency are found to be relatively modest, although boundary conditions appear to be important factors.
258Â citations
TL;DR: In this article, a review highlights time-resolved fluorescence kinetics and photon transport in tissues and other biomedical media with a special emphasis on ultrafast measurements of key optical parameters.
Abstract: This review highlights time-resolved fluorescence kinetics and photon transport in tissues and other biomedical media with a special emphasis on ultrafast measurements of key optical parameters. Measurements of fluorescence decay lifetimes from human breast and atherosclerotic artery tissues in the uv and visible region are described after a brief description of fundamentals of fluorescence kinetics. A time-dependent diffusion model for photon migration and various ultrafast methods for time-resolved light scattering measurements to obtain key optical parameters of tissues and other model turbid media are presented. The usefulness of optical parameters as markers in optical diagnostics and imaging is considered. Time-gated measurements of ballistic and snake photons to obtain shadowgrams and an inverse numerical reconstruction of the interior map of a turbid medium from time-resolved data in the context of optical tomography are presented.
255Â citations
TL;DR: Time-domain transmission imaging of an opaque structure in pork-fat tissue obtained with a terahertz (THz) field sampling technique shows significantly enhanced contrast, as a result of low scattering.
Abstract: We present time-domain transmission imaging of an opaque structure in pork-fat tissue obtained with a terahertz (THz) field sampling technique. Compared with imaging with near-infrared pulses, the terahertz sampling technique shows significantly enhanced contrast, as a result of low scattering. For enhanced spatial resolution, we show mid-infrared THz imaging of onion cells. Water absorption of THz pulse in muscle tissues is discussed.
238Â citations
References
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TL;DR: An ultrafast optical shutter was used to image ultrasmall objects hidden behind scattering walls by a procedure that selects in time the ballistic component and rejects the scattered diffusive light.
Abstract: An ultrafast optical shutter was used to image ultrasmall objects hidden behind scattering walls by a procedure that selects in time the ballistic component and rejects the scattered diffusive light. Scattering walls used in this experiment included human breast tissue, chicken breast tissue, and a water suspension of polystyrene particles with scattering coefficients up to 21.7. Submillimeter resolution was achieved for two-dimensional ballistic images of a single point, a double-point fluorescence source, and a bar test chart in or behind these different turbid media.
560Â citations
TL;DR: Photons are found to arrive earlier than that predicted by the diffusion theory as z/${\mathit{l}}_{\mathit-t}}$ becomes smaller or the anisotropic scattering increases.
Abstract: The transport of photons through a slab of random medium is shown to deviate from the diffusion approximation when z/${\mathit{l}}_{\mathit{t}}$ is small, where z is the thickness of the slab and ${\mathit{l}}_{\mathit{t}}$ is the transport mean free path. When z/${\mathit{l}}_{\mathit{t}}$=10 and z=10 mm, the average time of arrival is about 0.9 times that predicted by diffusion theory. Photons are found to arrive earlier than that predicted by the diffusion theory as z/${\mathit{l}}_{\mathit{t}}$ becomes smaller or the anisotropic scattering increases.
296Â citations
TL;DR: A time-gated technique to improve the possibility of localizing spatial differences in absorption when transilluminating a turbid, highly scattering medium, such as human tissue, is demonstrated.
Abstract: A time-gated technique to improve the possibility of localizing spatial differences in absorption when transilluminating a turbid, highly scattering medium, such as human tissue, is demonstrated. When transmitting picosecond laser pulses and detecting photons on the opposite side of the object, the contrast can be strongly enhanced by detecting only the photons with the shortest traveling time. Measurements on a 35-mm-thick tissue phantom with 5-mm-diameter absorbing objects inside are reported with data for a human hand in vivo. Implications for optical mammography (diaphanography) are discussed.
278Â citations
TL;DR: Angle- and time-resolved studies are presented for an ultrafast laser pulse propagating through a slab of random media in the intermediate scattering regime, where a coherent (ballistic) component coexists with a incoherent (diffusive) component in the forward-scattered light.
Abstract: Angle- and time-resolved studies are presented for an ultrafast laser pulse propagating through a slab of random media in the intermediate scattering regime, where a coherent (ballistic) component coexists with a incoherent (diffusive) component in the forward-scattered light. The incoherent component can be approximated by diffusion theory when the thickness of the slab is greater than 10 transport mean free paths. The theoretical results from the two-frequency coherence function in the Rytov approximation are in qualitative but not quantitative agreement with the experimental results.
234Â citations
TL;DR: Transmission images through a highly scattering medium have been obtained using picosecond pulses of visible light to develop one- and two-dimensional images of objects whose optical thicknesses are comparable with those of the human breast at visible wavelengths.
Abstract: Transmission images through a highly scattering medium have been obtained using picosecond pulses of visible light. The imaging method involves recording and discriminating between the times-of-flight of photons that penetrate the medium and using a fraction of the light with the shortest travel times to construct an image. The technique is being developed as a possible alternative method of screening for breast cancer without using potentially harmful x-rays. One- and two-dimensional images are presented of objects whose optical thicknesses are comparable with those of the human breast at visible wavelengths.
188Â citations