Protoporphyrin IX (PpIX) is a fluorophore being currently used to localize tumoral tissues. The tissue is usually excited at one wavelength, e.g., 405 nm, and the fluorescence signal is used to estimate the amount of PpIX during surgery. However, other fluorophores (baseline) whose emission spectra are close to the one of PpIX impair the quantification of PpIX and consequently the tissue pathological status classification. An efficient multi-excitation wavelengths method, free from any a priori on the baseline shape, has been proposed to cope with this issue. This method requires decorrelated measurements in the range of PpIX emission at multiple excitation wavelengths. We investigated the influence of the source bandwith on this decorelation by comparing two experimental setups using either LED or laser diode sources. The experimental setup using laser diodes for excitation increases the decorrelation by 35.3 % compared to the one using LEDs in the spectral range of PpIX emission.
Protoporphyrin IX (PpIX) is a fluorophore now used to identify tumoral tissues. The tissue is usually excited at one wavelength, e.g., 405 nm, and the fluorescence signal generated by this molecule and other fluorophores (the baseline) is used to estimate the amount of PpIX. However, fluorophores too close to PpIX impair the estimation and resulting classifications. Thus, we handle this issue by suggesting an efficient multi-excitation wavelengths method, free from any a priori on the baseline. Our method aims to distinguish healthy tissues from tumor margins, while being more robust to baseline variability. It keeps an ability to distinguish healthy from tumor tissues up to 87% in cases where existing methods’ ability drops near 0%.
In this presentation, we discuss the implications of increasing requirements on angular resolution in measuring the BRDF, the Bidirectional Reflection Diffusion Function, in particular for the control of manufactured artefacts. To account for fast angular variations with respect to the direction of illumination or to the direction of observation, coherence requirements increase, and speckle appears. However, speckle should not be considered as part of the BRDF. Means to adjust the definition of the BRDF and to circumvent the effect of speckle include an analysis of spatial and temporal coherence in the characterization instruments. In particular, the effects of spectral width on the speckle features in scattering diagrams are discussed qualitatively.
KEYWORDS: Luminescence, Error analysis, Tissues, Tumors, Fluorescence spectroscopy, In vivo imaging, Quantum efficiency, Magnetic resonance imaging, Brain, Surgery
We present a methodology for PpIX parameters estimation based on multi-wavelength excitation. This method aims to distinguish healthy tissues from tumour margins. It reduces the absolute estimation error of low density margins by 39.9%.
Gliomas are diffuse brain tumors still hardly curable due to the difficulties to identify their margins. 5-ALA induced PpIX fluorescence measurements have enabled to gain in sensitivity for discriminating margin from healthy tissue but they remain limited. In this study, we assume that two states of PpIX contribute to total fluorescence. We show that fluorescence in low density margins of high grade gliomas or in low grade gliomas comes mainly from PpIX peak centered at 620 nm. These results could help to improve fluorescence-guided resection of gliomas by discriminating healthy tissues from tumor margins.
Hyperspectral imaging has shown great potential for optical skin analysis by providing noninvasive, pixel-by-pixel surface measurements from which, applying an optical model, information such as melanin concentration and total blood volume fraction can be mapped. Such applications have been successfully performed on small flat skin areas, but existing methods are not suited to large areas such as an organ or a face, due to the difficulty of ensuring homogeneous illumination on complex three-dimensional (3-D) objects, which leads to errors in the maps. We investigate two methods to account for these irradiance variations on a face. The first one relies on a radiometric correction of the irradiance, using 3-D information on the face’s shape acquired by combining the hyperspectral camera with a 3-D scanner; the second relies on an optimization metric used in the map computation, which is invariant to irradiance. We discuss the advantages and drawbacks of the two methods, after having presented in detail the whole acquisition setup, which has been designed to provide high-resolution images with a short acquisition time, as required for live surface measurements of complex 3-D objects such as the face.
Most existing methods using hyperspectral imaging (HSI) to estimate skin chromophore concentrations fail to give an account of scattering properties crucial to many medical applications. To address this limitation, we propose to combine HSI with spatial frequency domain imaging (SFDI). Total acquisition time is around five seconds, making the process suitable for in vivo application. Skin absorption and scattering analysis is performed from these images by successive optimizations on the absorption and scattering properties. The problem of shadows occurring on complex shapes such as the face is addressed by an original approach that make results robust to irradiance drift.
5-ALA-induced protoporphyrin IX (PpIX) has shown its relevance in medical assisting techniques, notably in the detection of glioma (brain tumors). Validation of instruments on phantoms is mandatory and a standardization procedure has recently been proposed. This procedure yields phantoms recipes to realize a linear relationship between PpIX concentration and fluorescence emission intensity. The present study puts forward phantoms where this linear relationship cannot be used. We propose a model that considers two states of PpIX, corresponding to two different aggregates of PpIX, with fluorescence spectra peaking at 634 and 620 nm, respectively. We characterize the influence of these two states on PpIX fluorescence emission spectra in phantoms with steady concentration of PpIX and various microenvironment parameters (surfactant, Intralipid or bovine blood concentration, and pH). We show that, with fixed PpIX concentration, a modification of the microenvironment induces a variation of the emitted spectrum, notably a shift in its central wavelength. We show that this modification reveals a variation of proportions of the two states. This establishes phantom microenvironment regimes where the usual single state model is biased while a linear combination of the two spectra enables accurate recovering of any measured spectra.
We show the feasibility of using an intraoperative spectroscopic device to identify tumors margins during glioma resection. The collected fluorescence spectra is fitted with two reference spectra of PpIX and the contribution of each spectrum enables to overcome the sensitivity of current techniques by seeing tumor margins and low grade gliomas.
Fast and easy preview of a fabric without having to produce samples would be very profitable for textile designers, but
remains a technological challenge. As a first step towards this objective, we study the possibility of making images of a
real sample, and changing virtually the colors of its yarns while preserving the shine and shadow texture. We consider
two types of fabrics: Jacquard weave fabrics made of polyester warp and weft yarns of different colors, and satin ribbons
made of polyester and metallic yarns. For the Jacquard fabric, we make a color picture with a scanner on a sample in
which the yarns have contrasted colors, threshold this image in order to distinguish the pixels corresponding to each
yarn, and accordingly modify their hue and chroma values. This method is simple to operate but do not enable to
simulate the angle-dependent shine. A second method, tested on the satin ribbon made of black polyester and achromatic
metallic yarns, is based on polarized imaging. We analyze the polarization state of the reflected light which is different
for dielectric and metallic materials illuminated by polarized light. We then add a fixed color value to the pixels
representing the polyester yarns and modify the hue and chroma of the pixels representing the metallic yarns. This was
performed for many incident angles of light, in order to render the twinkling effect displayed by these ribbons. We could
verify through a few samples that the simulated previews reproduce real pictures with visually acceptable accuracy.
We investigate the optical phenomenon responsible for the colored shine that sometimes appears at the surface of ink
layers in the specular direction, often called bronzing or gloss differential. It seems to come from the wavelength-dependent
refractive index of the ink, which induces a wavelength-dependent reflectance of the ink-air interface. Our
experiments on cyan and magenta inkjet inks confirm this theory. Complex refractive indices can be obtained from
measurements of the spectral reflectance and transmittance of a transparency film coated with the ink. We propose a
correction of the classical Clapper-Yule model in order to include the colored gloss in the prediction of the spectral
reflectance of an inked paper. We also explored effects of scattering by the micrometric or nanometric roughness of the
ink surface. The micrometric roughness, easy to model with a geometrical optics model, can predict the spreading of the
colored gloss over a large cone. Electromagnetic models accounting for the effect of the nanometric roughness of the
surface also predict the attenuation of short wavelengths observed under collimated illumination.
Color calibration of imaging devices has been previously studied in a varied number of situations where the materials observed have diffuse or only slightly specular surfaces. Most of the calibration methods available in the literature consist in using standard diffuse color charts in order to determine the mathematical operations necessary to transform the colors measured by the imaging device into the reference colors obtained from the target chart. Unfortunately, there are many problems, such as sensor saturation, that arise when using these methods to calibrate devices intended for the observation of highly specular samples, especially in the 0°:0° illumination/observation geometry used in microscopic imaging systems. In this paper, we explore several color calibration methods adapted for the observation of highly specular materials, and propose one method in particular in which we use colored filters and a calibrated mirror in order to obtain a set of specular colored samples. By using 72 samples for learning, we tested the different methods on 50 other samples and obtained, with the best one, an average CIE-DeltaE94 color difference of 1.93 units, which is a fairly good performance for color measurements at the microscopic scale.
This paper introduces a homogeneity assessment method for the printed versions of uniform color images. This parameter has been specifically selected as one of the relevant attributes of printing quality. The method relies on image processing algorithms from a scanned image of the printed surface, especially the computation of gray level co-occurrence matrices and of objective homogeneity attribute inspired of Haralick's parameters. The viewing distance is also taken into account when computing the homogeneity index. Resizing and filtering of the scanned image are performed in order to keep the level of details visible by a standard human observer at short and long distances. The combination of the obtained homogeneity scores on both high and low resolution images provides a homogeneity index, which can be computed for any printed version of a uniform digital image. We tested the method on several hardcopies of a same image, and compared the scores to the empirical evaluations carried out by non-expert observers who were asked to sort the samples and to place them on a metric scale. Our experiments show a good matching between the sorting by the observers and the score computed by our algorithm.
The well-known Yule-Nielsen modified spectral Neugebauer model is one of the most accurate predictive models for the spectral reflectance of printed halftone colors which expresses the spectral reflectance of halftones raised to the power 1/n as a linear combination of the spectral reflectance of the fulltone colors (Neugebauer primaries) also raised to the power 1/n, where n is a tunable real number. The power 1/n transform, characteristic of the Yule-Nielsen transform, empirically models the nonlinear relationship between the spectral reflectances of halftones and fulltones due to the internal propagation of light by scattering into the printing support, a phenomenon known as “optical dot gain” or “Yule- Nielsen effect”. In this paper, we propose a graphical method permitting to observe this non-linear relationship in the case of single-ink halftones and to experimentally check the capacity of the Yule-Nielsen model to predict it accurately. In the case where the Yule-Nielsen transform is not well adapted to the considered type of prints, we propose alternative transforms in order to improve the prediction accuracy.
Laser-induced periodic surface structures, also known as ripples, have been investigated for a long time on various materials. They are self-organized grating-like structures that form spontaneously upon irradiation with a single laser beam; their formation requiring a high temperature rise, it generally results from interactions with ultrashort laser pulses. Recently, similar phenomena leading to periodic changes in the morphology of metallic nanoparticles embedded in polymer films have been reported under femtosecond laser exposure. Here, we demonstrate that chain-like self-organized silver nanoparticles can be grown, from an ionic silver precursor, within titania films under continuous wave visible laser beam. The nanoparticle chains are periodically spaced with a period that depends on the wavelength and are oriented parallel to the laser polarization. The samples present no significant surface modulation since all of the grown nanoparticles are located at the substrate-film interface, protected by a crystallized TiO2 film. SEM, TEM, HRTEM and EDX characterizations of the film nanostructuring are shown. Due to the coupling of incident light to a guided mode of the TiO2 film by the first diffraction order of the NP grating, such samples exhibit a strong dichroism whose characteristics depend on the laser exposure conditions. Color changes and spectral variations with polarization are measured and interpreted. The high stability of such colored films under high temperature rises or high intensity UV or visible exposures is demonstrated; it makes them good candidates for colored data storage.
The present work investigates the transmission of light through stacks of halftone printed transparencies. We propose a
spectral transmittance model describing the multiple reflections of light between the transparencies, whose individual
reflectance and transmittance have themselves been obtained by a prediction model. The model for single printed
transparency involves the multiple reflections of light between the interfaces as well as the orientation-dependent
attenuations of light within the plastic and ink layers. A procedure enables converting the nominal ink surface coverages
into effective ones by taking into account the spreading of the inks. Calibration of the model is based on printing a small
number of color patches on one transparency and measuring their spectral transmittance. Regarding the stacks of
transparencies, an experimental test carried out with inkjet printed samples shows good agreement between predictions
and measurements for stacks of two, three and four transparencies. Stochastic halftones are used in order to avoid the
apparition of moiré patterns when superposing the halftones. By inversion of the model, we are able to determine the
halftone colors to print on each transparency in order to obtain by superposition one targeted color. An original
application of this, called "color matching", consists in producing one color of stack from various combinations of colors
on the transparencies. The prediction accuracy of the proposed model guarantees the good visual uniformity of the
resulting colored area.
The color of prints is mainly determined by the light absorption of the inks deposited on top of paper. In order to predict
the reflectance spectrum of prints, we use a spectral prediction model in which each ink is characterized by its spectral
transmittance. In the present paper, we consider two classical reflectance prediction models: the Clapper-Yule model and
the Williams-Clapper model. They rely on a same description of multiple reflection-transmission of light, but use a
different description of the attenuation of light by the inks. In the Clapper-Yule model (non-orientational ink
attenuation), the orientation of light traversing the ink is not taken into account. In the Williams-Clapper model, it is
taken into account (orientational ink attenuation). In order to determine experimentally which of these two models is the
more suitable for a given type of print, we propose a method using the reflectance and the transmittance of prints. We
introduce a bimodal model, enabling spectral reflectance and transmittance predictions. Depending whether the direction
of light into the ink is taken into account, we obtain a non-orientational bimodal model or an orientational bimodal
model. Using these two models, we deduce the ink transmittance spectrum from various reflectance and transmittance
measurements performed on a same print, and compare the different deduced spectra. The model which is the most
adapted to the considered print is the one where the deduced spectra best match each other.
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