Among the diverse applications of silica nanoparticles, the suitability of these to reproduce scattering and absorption properties in tissue simulating phantoms for diffuse optical imaging, through the use of Mie theory, has been recently proposed [1]. An important limitation to adjust the Mie theory to the pattern of scattered light by scattering spheres is the relative ratio between the wavelength of the incident light and the size of the scattering sphere, in this way, it is important to achieve monodisperse and controlled growth of the spheres diameter, so this ratio will be close to 1, allowing the Mie theory to work according to its own limitations.The development of diagnostic imaging systems has required the use of tissue simulating materials to mimic the optical properties of human or animal tissues [2,3]. The properties of these phantoms usually are inconsistent and change over time, making comparison of different imaging systems a serious problem when also different animal-derived phantoms are being used [4]. The use of a standard phantom suitable to be reproduced in any laboratory with constant and confident optical properties is the main goal of using silica nanoparticles to develop this standard.In this work a modified version of the Stöber Method [5,6] is used to obtain spherical silica particles by varying the proportion of water and ethanol contained in a solution while maintaining a constant proportion in the rest of the reagents: tetraethyl orthosilicate and hydroxide of ammonium. To analyze the structure of each sample the hydrodynamic diameters of SiO2 spheres were measured by dynamic light scattering (DLS) using a Malvern Zetasizer Nano Range analyzer. Then the nanoparticle diameters were measured by scanning electron microscopy (SEM) observing spherical and monodisperse particles; SEM analyses were carried on with a FE-SEM JEOL JSM-7800F.There are several methods for the synthesis of SiO2, we use a modified version of the Stöber Method. This method consists of controlled hydrolysis, catalyzed on alcoholic medium. The following precursors were used: tetraethylorthosilicate (TEOS, Si(OC2H5)4) as precursor of silica, ethanol and deionized water as solvents and ammonia hydroxide (NH4OH) as a catalyst; the synthesis took place at room temperature with magnetic stirring for 24 hours. Figure 1 shows the hydrodynamic diameter distribution of the particles as a function of the percentage of water diluted in ethanol, it is observed that in the range of 4 to 8% of water volume the diameter of the particle increases rapidly to around 750 nm, while outside this range the diameter of the nanoparticle decreases; these results are in relative agreement with others reported in the literature [6]. This controlled growth will allow to vary the wavelength used in accordance with de particle diameter. In Figure 2 the scattering silica nanoparticles SEM images are shown.

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Plasmonic photothermal therapy (PPTT), as an increasingly studied treatment alternative, has been widely regarded mostly as a surface tissue treatment choice. Although some techniques have been implemented for interstitial tumors, these involve some grade of invasiveness, as the outer skin is usually broken to introduce light-delivering optical fibers or even catheters. In this work, we present a potential non-invasive strategy using the stereotactic approach, long employed in radiosurgery, by converging multiple near infrared laser beams for PPTT in tissue-equivalent optical phantoms that enclose small gel spheres and simulate interstitial tissue impregnated with plasmonic nanoparticles. The real-time in-depth monitoring of temperature increase is realized by an infrared camera face-on mounted over the phantom. Our results show that a significant reduction in the surface heating can be achieved with this configuration while remarkably increasing the interstitial reach of PPTT, assuring a ∼ 6 ∘ C temperature increase for the simulated tumors at 10 mm depth and ∼ 4 ∘ C at 15 mm depth and opening up new possibilities for future clinical applications.

We describe the behavior of linearity in diffuse imaging by evaluating the differences between time-resolved images produced by photons arriving at the detector at different times. Two approaches are considered: Monte Carlo simulations and experimental results. The images of two complete opaque bars embedded in a transparent or in a turbid medium with a slab geometry are analyzed; the optical properties of the turbid medium sample are close to those of breast tissue. A simple linearity test was designed involving a direct comparison between the intensity profile produced by two bars scanned at the same time and the intensity profile obtained by adding two profiles of each bar scanned one at a time. It is shown that the linearity improves substantially when short time of flight photons are used in the imaging process, but even then the nonlinear behavior prevails. As the edge response function (ERF) has been used widely for testing the spatial resolution in imaging systems, the main implication of a time dependent linearity is the weakness of the linearity assumption when evaluating the spatial resolution through the ERF in diffuse imaging systems, and the need to evaluate the spatial resolution by other methods.

This paper discusses the main differences between two different methods for determining the optical properties of tissue optical phantoms by fitting the spatial and temporal intensity distribution functions to the diffusion approximation theory. The consistency in the values of the optical properties is verified by changing the width of the recipient containing the turbid medium; as the optical properties are an intrinsic value of the scattering medium, independently of the recipient width, the stability in these values for different widths implies a better measurement system for the acquisition of the optical properties. It is shown that the temporal fitting method presents higher stability than the spatial fitting method; this is probably due to the addition of the time of flight parameter into the diffusion theory.