There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

We describe the development of multifunctional nanoparticle probes based on semiconductor quantum dots (QDs) for cancer targeting and imaging in living animals. The structural design involves encapsulating luminescent QDs with an ABC triblock copolymer and linking this amphiphilic polymer to tumor-targeting ligands and drug-delivery functionalities. In vivo targeting studies of human prostate cancer growing in nude mice indicate that the QD probes accumulate at tumors both by the enhanced permeability and retention of tumor sites and by antibody binding to cancer-specific cell surface biomarkers. Using both subcutaneous injection of QD-tagged cancer cells and systemic injection of multifunctional QD probes, we have achieved sensitive and multicolor fluorescence imaging of cancer cells under in vivo conditions. We have also integrated a whole-body macro-illumination system with wavelength-resolved spectral imaging for efficient background removal and precise delineation of weak spectral signatures. These results raise new possibilities for ultrasensitive and multiplexed imaging of molecular targets in vivo.

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In vivo cancer targeting and imaging with semiconductor quantum dots

A review of reported tissue optical properties summarizes the wavelength-dependent behavior of scattering and absorption. Formulae are presented for generating the optical properties of a generic tissue with variable amounts of absorbing chromophores (blood, water, melanin, fat, yellow pigments) and a variable balance between small-scale scatterers and large-scale scatterers in the ultrastructures of cells and tissues.

/pdf/optical-properties-of-biological-tissues-a-review-2bu6kxou63.pdf

Optical properties of biological tissues: a review.

A Monte Carlo model of steady-state light transport in multi-layered tissues (MCML) has been coded in ANSI Standard C; therefore, the program can be used on various computers. Dynamic data allocation is used for MCML, hence the number of tissue layers and grid elements of the grid system can be varied by users at run time. The coordinates of the simulated data for each grid element in the radial and angular directions are optimized. Some of the MCML computational results have been verified with those of other theories or other investigators. The program, including the source code, has been in the public domain since 1992.

MCML-Monte Carlo modeling of light transport in multi-layered tissues

The known optical properties (absorption, scattering, total attenuation, effective attenuation, and/or anisotropy coefficients) of various biological tissues at a variety of wavelengths are reviewed. The theoretical foundations for most experimental approaches are outlined. Relations between Kubelka-Munk parameters and transport coefficients are listed. The optical properties of aorta, liver, and muscle at 633 nm are discussed in detail. An extensive bibliography is provided. >

A review of the optical properties of biological tissues

Pulsed photothermal radiometry (PPTR) measures blackbody radiation emitted by a sample after absorption of an optical pulse. Three techniques for obtaining the absorption coefficient of absorbing-only, semi-infinite samples are examined and shown to give comparable results. An analytic theory for the time dependence of the PPTR signal in semi-infinite scattering and absorbing media has been derived and tested in a series of controlled gel phantoms. This theory, based on the diffusion approximation of the radiative transport equation, is shown to model the time course of the detected signal accurately. Furthermore, when the incident fluence is known, the theory can be used in a non-linear two-parameter fitting algorithm to determine the absorption and reduced scattering coefficients of a turbid sample with an accuracy of 10-15% for transport albedos ranging from 0.42-0.88.

https://iopscience.iop.org/article/10.1088/0031-9155/37/6/001/pdf

Determination of optical properties of turbid media using pulsed photothermal radiometry

We describe a method for the preparation of a polyurethane phantom to simulate the optical properties of biologic tissues at two wavelengths in the visible and near-infrared spectral range. We char- acterize the addition of added molecular absorbers with relatively narrow absorption bands full width at half maximum FWHM 32 and 76 nm for Epolight 6084 and 4148, respectively for independent absorption at 690 nm for absorption up to 5c m �1 , and 830 nm for absorptions up to 3c m �1 . Absorption by both dyes is linear with con- centration in these respective regions and is consistent in polyure- thane both before and after curing. The dyes are stable over long durations with no more than 4% change. The absorption of visible light by polyurethane decreases with time and is stable by one year with a drop of 0.03±0.003 cm �1 from 500 to 830 nm. The scattering properties are selected by the addition of TiO2 particles to the poly- urethane, which we functionally describe for the 690- and 830-nm wavelengths as related to the weight per volume. We demonstrate that the variation in absorption and scattering properties for large batch fabrication 12 samples is ±3%. The optical properties of the phan- toms have not significantly changed in a period of exceeding one year, which makes them suitable for use as a reference standard. ©

/pdf/preparation-and-characterization-of-polyurethane-optical-3j6m2ae7bl.pdf

Preparation and characterization of polyurethane optical phantoms

Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide.

The accuracy of the diffusion approximation is compared with more accurate solutions for describing light interaction with biological tissues. Generally the diffusion approximation underestimates the light distribution in the surface region, and, for high albedos, it significantly underestimates the fluence rate. This difference is only a few percent for albedos of less than 0.5 due to the dominance of collimated light. As the anisotropy of scattering increases, deviations increase. In general, fluxes can be computed more accurately with the diffusion approximation than fluence rates. For anisotropic scattering, better results can be obtained by simple transforms of optical coefficients using the similarity relations. The similarity relations improve flux calculations, but computed fluence rates have substantial errors for high albedo and the large index of refraction differences at the surface.

Scott A. Prahl

Papers

Determination of optical properties of turbid media using pulsed photothermal radiometry

Preparation and characterization of polyurethane optical phantoms

Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide.

Accuracies of the diffusion approximation and its similarity relations for laser irradiated biological media

Quantum yield of conversion of the photoinitiator camphorquinone