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cote interne IRCAM: Bloit10a; None / None; National audience; We present a method to model sound descriptor temporal profiles using Segmental Models. Unlike standard HMM, such an approach allows for the modeling of fine structures of temporal profiles with a reduced number of states. These states, we called primitives, can be chosen by the user using prior knowledge, and assembled to model symbolic musical elements. In this paper, we describe this general methodology and evaluate it on a dataset made of of violin recording containing crescendo/decrescendo, glissando and sforzando. The results show that, in this context, the segmental model can segment and recognize these different musical elements with a satisfactory level.

cote interne IRCAM: Caramiaux09d; None / None; National audience; This article reports on the exploration of a method based on canonical correlation analysis (CCA) for the analysis of the relationship between gesture and sound in the context of music performance and listening. This method is a first step in the design of an analysis tool for gesture-sound relationships. In this exploration we used motion capture data recorded from sub jects performing free hand movements while listening to short sound examples. We assume that even though the relationship between gesture and sound might be more complex, at least part of it can be revealed and quantified by linear multivariate regression applied to the motion capture data and audio descriptors extracted from the sound examples. After outlining the theoretical background, the article shows how the method allows for pertinent reasoning about the relationship between gesture and sound by analysing the data sets recorded from multiple and individual subjects.

We describe the development of a rapid, noncontact imaging method, modulated imaging (MI), for quantitative, wide-field characterization of optical absorption and scattering properties of turbid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function (s-MTF). We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l*values (0.5mmto3mm) and (μs′/μa) ratios (8 to 500), reporting an overall accuracy of approximately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate determination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the absorption and scattering optical contrast in a human forearm and dynamic measurements of a forearm during venous occlusion. Last, metrics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms. © 2009 Society of Photo-Optical Instrumentation Engineers.

cote interne IRCAM: Leslie09a; None / None; National audience; Wavefield synthesis (WFS), the spatialization of audio through the recreation of a virtual source’s wavefront, is uniquely suited to interactive applications where listeners move throughout the rendering space and more than one listener is involved. This paper describes the features of WFS that make it useful for interactive applications, and takes a recent project at Ircam as a case study which demonstrates these advantages. The interactive installation GrainStick was developed as a collaboration between the composer Pierre Jodlowski and the European project Sound And Music For Everyone Everyday Everywhere Everyway (SAME) at Ircam, Paris. The interaction design of GrainStick presents a new development in multimodal interfaces and multichannel sound by allowing users control of their auditory scene through gesture analysis performed on infrared camera motion tracking and accelerometer data.

A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain (FD) and steady-state (SS) reflectance methods is presented. Most of the wavelength coverage is provided by a white-light SS measurement, whereas the FD data are acquired at a few selected wavelengths. Coefficients of absorption (μa) and reduced scattering (μ‘s) derived from the FD data are used to calibrate the intensity of the SS measurements and to estimate μ‘s at all wavelengths in the spectral window of interest. After these steps are performed, one can determine ma by comparing the SS reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined SSFD technique, agree well with expected reference values. All measurements can be performed at a single source-detector separation distance, reducing the variations in sampling volume that exist in multidistance methods. The technique uses relatively inexpensive light sources and detectors and is easily implemented on an existing multiwavelength FD system. © 2000 Optical Society of America.

cote interne IRCAM: Rasamimanana08c; National audience; Anticipatory behaviours are known to occur in music performance, notably on the control movements of instruments such as piano or drums. We studied such effects on bowed string movements, corresponding to a case where the control on sound is continuous. Movements were measured with an optical motion capture system combined with sensors on the bow. Bowing movements were analysed and compared on the basis of underlying effort costs, determined from their velocity profiles. Precisely, we used movement models that assume that jerk or impulse are minimized. These models were synthesized based on measurement data and then compared to velocity and acceleration profiles. Results on various musical cases involving separate strokes, scales, mixed bowing techniques and rhythms showed that this methodology can account, to some extent, for the different effort strategies used by the players. The presented modelling provides evidence of anticipatory behaviour during bowing movements.

cote interne IRCAM: DeLahunta07a; None / None; National audience; In this essay the authors report on the findings of the one-day workshop called Choreographic Computations: Motion Capture and Analysis for Dance held at IRCAM (Institute for music/acoustic research and coordination) in Paris in June 2006. The focus of the workshop was on new innovations combining motion capture and computer-based techniques with choreography and performance. An international group of artist programmers and dance makers who are bringing complex algorithmic procedures into alignment with choreographic creation were invited to give presentations and discuss, with each other and the invited audience, the shared understanding of movement and gesture they are developing.

cote interne IRCAM: Rasamimanana09a; National audience; The understanding of different bowing strategies can provide key concepts for the modelling of music performance. We report here an exploratory study of bowing gestures for a viola player and a violin player in the case of bow strokes performed at different frequencies. Bow and arm movements as well as bow pressure on strings were measured respectively with a 3D optical motion capture system and a custom pressure sensor. While increasing bow stroke frequency, defined as the inverse time between two strokes, players did use different bowing movements as indicated from the measurement of bow velocity and arm joint angles. First, bow velocity profiles abruptly shift from a rectangle shape to a sinus shape. Second, while bow velocity is sinusoidal, an additional change is observed: the wrist and elbow relative phase shifts from out-of-phase to in-phase at the highest frequencies, indicating a possible change in the players coordinative pattern. We finally discuss the fact that only small differences are found in the sound while significant changes occur in the velocity / acceleration profiles.

cote interne IRCAM: Bevilacqua07a; None / None; National audience; We present in this paper a complete gestural interface built to support music pedagogy. The development of this prototype concerned both hardware and software components: a small wireless sensor interface including accelerometers and gyroscopes, and an analysis system enabling gesture following and recognition. A first set of experiments was conducted with teenagers in a music theory class. The preliminary results were encouraging concerning the suitability of these developments in music education.

International audience; Bien que le monde du son ait évolué de concert avec les progrès technologiques, le monde des images semble dominer notre perception. Par exemple, la réalité virtuelle (RV) est bien souvent la métaphore inconsciente d'une réalité virtuelle visuelle, et les applications de RV, qu'elles relèvent du jeu, de l'apprentissage ou même de l'art, s'adressent principalement à la vision. On sait l'importance des notions d'espace et d'interaction pour promouvoir la sensation de présence dans des environnements virtuels. Cependant, peu de travaux s'attachent à exploiter le potentiel fourni par les stimulations virtuelles s'adressant au système auditif de l'utilisateur. Nous présentons ici le projet EarToy, dont l'objectif vise à mettre à jour les liens existant entre audition et action, afin de construire des systèmes immersifs et interactifs basés sur la perception auditive.

We present results demonstrating the capabilities of spatially modulated illumination methods to enable high-resolution tomography and quantitative spectral imaging in turbid biological systems.

cote interne IRCAM: Rasamimanana06a; None / None; National audience; We developed an ”augmented violin”, i.e. an acoustic instrument with added gesture capture capabilities to control electronic processes. We report here gesture analysis we performed on three different bow strokes, detache, martele and spiccato, using this augmented violin. Different features based on velocity and acceleration were considered. A linear discriminant analysis has been performed to estimate a minimum number of pertinent features necessary to model these bow stroke classes. We found that the maximum and minimum accelerations of a given stroke were efficient to parameterize the different bow stroke types, as well as differences in dynamics playing. Recognition rates were estimated using a kNN method with various training sets. We finally discuss that bow stroke recognition allows to relate the gesture data to music notation, while a bow stroke continuous parameterization can be related to continuous sound characteristics.

Experiments performed on turbid phantoms demonstrate that spatially modulated illumination facilitates quantitative wide-field optical property mapping and tomographic imaging in turbid media.

cote interne IRCAM: Bevilacqua05b; None / None; National audience; Our aim is to develop a gesture follower for performing arts, which indicates inreal-time the time correspondences between an observed gesture sequence and a fixed reference gesture sequence (or in other words to time warp in real-time theobserved sequence to the learned sequence). Applications concern for example choreography or (composed) music. The possibility to continuously establishcorrespondences between observed and reference gestures has important potentials. For example, this will enable the quantitative comparison of gesture data, at similarmoments, between live and previously recorded performances. Particularly, this should facilitate the computation of parameters related to interpretation andexpression. Moreover, this will also provide new tools to control and dynamically change mapping settings between gesture and digital media.

We demonstrate the ability of Modulated Imaging to linearly and accurately recover absorption and scattering optical properties from experiments on homogeneous turbid phantoms. Examples of in-vivo property mapping on human skin and rodent cortex are also presented.

We introduce a robust method to recover optical absorption, reduced scattering, and single-scattering asymmetry coefficients (microa, micro's, g1) of infinite turbid media over a range of (micro's/microa) spanning 3 orders of magnitude. This is accomplished through the spatially resolved measurement of irradiance at source-detector separations spanning 0.25-8 transport mean free paths (l*). These measurements are rapidly processed by a multistaged nonlinear optimization algorithm in which the measured irradiances are compared with predictions given by the delta-P1 variant of the diffusion approximation to the Boltzmann transport equation. The ability of the delta-P1 model to accurately describe radiative transport within media of arbitrary albedo and on spatial scales comparable to l* is the key element enabling the separation of g1 from micro's.

We demonstrate the use of Monte Carlo simulations to generate photon scattering density functions (PSDFs) that represent the tissue volume sampled by steady-state and frequency-domain photon migration. We use these results to illustrate how scaling laws can be developed to determine the mean sampling depth of the multiply scattered photons detected by photon migration methods that remain valid outside the bounds of the standard diffusion approximation, i.e., at small source-detector separations and in media where the optical absorption is significant relative to scattering. Using both the PSDF computation and the newly formulated scaling laws, we focus on a comprehensive description of the effects of source modulation frequency, optical absorption, and source-detector separation on the depth of the sampled tissue volume as well as the sensitivity of frequency-domain photon migration measurements to the presence of a localized absorption heterogeneity.

Presurgical chemotherapy is widely used in the treatment of locally advanced breast cancer. Monitoring the response to therapy can improve survival and reduce morbidity. We employ a noninvasive, near-infrared method based on diffuse optical spectroscopy (DOS) to quantitatively monitor tumor response to neoadjuvant chemotherapy. DOS was used to monitor tumor response in one patient with locally advanced breast cancer throughout the course of her therapy. Measurements were performed prior to doxorubicin-cyclophosphamide therapy and at several time points over the course of three treatment cycles (68 days). Our results show strong tumor to normal (T/N) tissue contrast in total hemoglobin concentration (T/N =2.4), water fraction (T/N=6.9), tissue hemoglobin oxygen saturation, StO2(T/N=0.9), and lipid fraction (T/N=0.7) prior to treatment. Over a 10-week period, the peak total hemoglobin and water dropped 56 and 67%, respectively. Lipid content nearly returned to baseline (T/ N = 0.9) while StO2exceeded pretreatment levels (T/N = 1.5). Approximately half of the hemoglobin and water changes occurred within 5 days of treatment (26 and 37%, respectively). These data suggest that noninvasive, quantitative optical methods that characterize tumor physiology may be useful in assessing and optimizing individual response to neoadjuvant chemotherapy. © 2004 Society of Photo-Optical Instrumentation Engineers.

We use Monte Carlo techniques to address inverse problems in heterogeneous media. The techniques we develop are general and do not rely on specific geometries or material properties.

Experiments performed on heterogeneous and homogeneous tissue-simulating phantoms demonstrate that spatially modulated illumination enables depth-resolved imaging and wide-field optical property mapping in turbid media.

We report coregistration of near-infrared diffuse optical spectroscopy (DOS) and magnetic resonance imaging (MRI) for the study of animal model tumors. A combined broadband steady-state and frequency-domain apparatus was used to determine tissue oxyhemoglobin, deoxyhemoglobin, and water concentration locally in tumors. Simultaneous MRI coregistration provided structural (T2-weighted) and contrast-enhanced images of the tumor that were correlated with the optical measurements. By use of Monte Carlo simulations, the optically sampled volume was superimposed on the MR images, showing precisely which tissue structure was probed optically. DOS and MRI coregistration measurements were performed on seven rats over 20 days and were separated into three tumor tissue classifications: viable, edematous, and necrotic. A ratio of water concentration to total hemoglobin concentration, as measured optically, was performed for each tissue type and showed values for edematous tissue to be greater than viable tissue (1.2 +/- 0.49 M/microM versus 0.48 +/- 0.15 M/microM). Tissue hemoglobin oxygen saturation (StO2) also showed a large variation between tissue types: viable tissue had an optically measured StO2 value of 61 +/- 5%, whereas StO2 determined for necrotic tissue was 43 +/- 6%.

We demonstrate that spatially modulated illumination can recover depth sensitive images of targets embedded in turbid media. Experiments were performed on tissue-simulating phantoms with superficial and subsurface absorption heterogeneities. Depth sensitivity is demonstrated to depend on spatial frequency of the illumination and on the optical properties of the sample.

The dynamics of optical contrast agents are measured in an adenocarcinoma rat tumor model using a combined frequency-domain and steady-state optical technique. Compartmental modeling of contrast agent dynamics allows quantification of physiologic parameters such as capillary permeability and blood flow. Optically-derived parameters are compared to those measured by contrast-enhanced MRI.

Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR techniques are based on quantitative measurements of functional contrast between healthy and diseased tissue. In this study we measured the spectral dependence of tissue absorption (μa) and reduced scattering (μ's) in the breasts of 30 healthy women and one woman with a fibroadenoma using a seven-wavelength frequency-domain photon migration probe. Subjects included pre- and postmenopausal women between the ages of 18 and 64. Multi-spectral measurements were used along with a four-component fit to determine the concentrations of de-oxy and oxyhemoglobin, water and lipids in breast. The scattering spectral shape was also quantified. Our measurements demonstrate that the measured concentrations of NIR analytes correlate well with known breast physiology. Although the tissue scattering at a single wavelength was found to have little value as a functional parameter, the dependence of the scattering on wavelength provided key insights into breast composition and physiology. Lipids and scattering spectra in the breast were found to increase and decrease, respectively, with increasing body mass index. Simple calculations are also provided to demonstrate potential penalties from ignoring the contributions of water and lipids in breast measurements. Finally, water is shown to be a possible indicator for detecting a fibroadenoma, whereas the hemoglobin saturation was found to be a poor indicator. Multi-spectral measurements, compared to measurements restricted to one or two wavelengths, provide additional information that may be useful in managing breast disease. © 2002 Society of Photo-Optical Instrumentation Engineers.

Illumination with structured light allows for subsurface imaging and the determination of the optical properties over a large area. Both the average and the spatial variation of the optical properties can be determined.

NIR tissue spectroscopy was used to monitor a breast cancer patient during three cycles of presurgical chemotherapy. Lesion values of lipid, water, deoxygenated and oxygenated hemoglobin changed significantly within the first week, and continued to change throughout therapy.

A technique for measuring broadband near-infrared absorption spectra of turbid media is presented using a combination of frequency-domain (FD) and steady-state (SS) reflectance methods. Most of the wavelength coverage is provided by a white-light SS measurement, while the FD data are acquired at a few selected wavelengths. Coefficients of absorption ((mu) a) and reduced scattering ((mu) s') derived from the FD data are used to intensity-calibrate the SS measurements and to estimate (mu) s' at all wavelengths in the spectral window of interest. After these steps are performed, (mu) a can be determined by comparing the SS reflectance values to the predictions of diffusion theory, wavelength by wavelength. We present an application of this method to breast tumor characterization. A case study of a fibroadenoma is shown, where different absorption spectra were found between the normal and the tumor sides.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Near infrared diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR spectroscopy yields quantitative functional information that cannot be obtained with other non-invasive radiological techniques. In this study we focused upon the origins of this contrast in healthy breast, especially from water and lipids.

Rationale and Objectives Near-infrared (NIR) diffuse optical spectroscopy and imaging may enhance existing technologies for breast cancer screening, diagnosis, and treatment. NIR techniques are based on sensitive, quantitative measurements of functional contrast between healthy and diseased tissue. In this study, the authors quantified the origins of this contrast in healthy breasts. Materials and Methods A seven-wavelength frequency-domain photon migration probe was used to perform noninvasive NIR measurements in the breasts of 28 healthy women, both pre- and postmenopausal, aged 18–64 years. A diffusive model of light transport quantified oxygenated and deoxygenated hemoglobin, water, and lipid by their absorption signatures. Changes in the measured light-scattering spectra were quantified by means of a “scatter power” parameter. Results Substantial quantitative differences were observed in both absorption and scattering spectra of breast as a function of subject age. These physiologic changes were consistent with long-term hormone-dependent transformations that occur in breast. Instrument response was not adversely affected by subject age or menopausal status. Conclusion These measurements provide new insight into endogenous optical absorption and scattering contrast mechanisms and have important implications for the development of optical mammography. NIR spectroscopy yields quantitative functional information that cannot be obtained with other noninvasive radiologic techniques.

A method was described for using steady-state and frequency-domain reflectance measurements to obtain broad wavelength quantitative data with deep tissue penetration. Fundamental information on tissue biochemistry and structure was provided using the wavelength-dependence of absorption and scattering parameters. Results showed that total hemoglobin content, water and lipid percentage can be measured using this technique.

Absorption (mu (a)) and reduced scattering (mu (s)') spectra of turbid media were quanti fied with a noncontact imaging approach based on a Fourier-transform interferometric imaging system (FTIIS). The FTIIS was used to collect hyperspectral images of the steady-state diffuse reflectance from turbid media. Spatially resolved reflectance data from Monte Carlo simulations were fitted to the recorded hyperspectral images to quantify mu (a) and mu (s)' spectra in the 550-850-nm region. A simple and effective calibration approach was introduced to account for the instrument response. With reflectance data that were close to and far from the source (0.5-6.5 mm), mu (a) and mu (')(s) of homogeneous, semi-infinite turbid phantoms with optical property ranges comparable with those of tissues were determined with an accuracy of +/-7% and +/-3%, respectively. Prediction accuracy for mu (a) and mu (s)' degraded to +/-12% and +/-4%, respectively, when only reflectance data close to the source (0.5-2.5 mm) were used. Results indicate that reflectance data close to and far hom the source are necessary for optimal quantification of mu (a) and mu (s)'. The spectral properties of mu (a) and mu (s)' values were used to determine the concentrations of absorbers and scatterers, respectively. Absorber and scatterer concentrations of two-chromophore turbid media were determined with an accuracy of +/-5% and +/-3%, respectively. (C) 2000 Optical Society of America OCIS codes: 170.0110, 170.7050, 170.6510, 070.2590, 120.3180.

Different techniques have been proposed to correlate optical properties of tissue and their physiology/pathology. In this paper, we describe a new optical biopsy method based on spatially resolved reflectance measurement using a small diameter probe (o1.8 mm). The development of an appropriate model for photon propagation in tissue at such distances allows us to determine simultaneously reduced scattering coefficient µs’ and absorption coefficient µa. Being made spectroscopically, the measurements then provide information both on tissue structure (related to scattering coefficient) and chromophore content (related to absorption coefficient). Such features can be used to distinguish between normal tissues and various pathologies. We present the guidelines of the method and preliminary results obtained on mice, where significant contrast has been observed between normal and altered epidermis and dermis.

Frequency-domain Monte Carlo simulations are performed to study how amplitude and phase measurements, at various frequencies and source-detector separations, can sample different tissue volumes. Homogeneous and heterogeneous tissues are investigated.

Local and superficial optical property characterization of biological tissues can be performed by measuring spatially-resolved diffuse reflectance at small source-detector separations. Monte Carlo simulations and experiments were performed to assess the performance of a spatially-resolved reflectance probe, employing multiple detector fibers (0.3 to 1.4 mm from the source). Under these conditions, the inverse problem, i.e. calculating the absorption and reduced scattering coefficients, is necessarily sensitive to the phase function. This effect must be taken into account by considering a new parameter of the phase function, which depends on the first and second moments of the phase function. Probe performance is compared to another technique for quantitatively measuring optical coefficients, based on the analysis of photon density waves (Frequency Domain Photon Migration). The two techniques are found to be in reasonable agreement. However, the spatially resolved probe shows optimum measurement sensitivity in the volume immediately beneath the probe, while FDPM typically samples much larger regions of tissues. Measurements on human brain in vivo are reported using both methods.

Different techniques have been proposed for optical biopsy purposes, such as fluorescence spectroscopy1, elastic scattering spectroscopy2 or optical coherence tomography1.

Photon Migration through diffusive media studied in the frequency-domain is characterized by Diffuse Photon Density Waves (DPDWs). Theoretically, DPDWs propagation is described using the diffraction theory based on the diffusion approximation to the transport equation. Experimentally, 100 MHz modulated DPDWs are generated with our home-made frequency-domain set-up. The actual accuracy of this set-up is 0.3% in amplitude and 0.15 degree(s) in phase. The diffuse media probed are (optical)-breast-like phantoms which contain 5 mm-diameter inhomogeneities with inhomogeneity/background absorption and scattering contrasts of 1.1, 1.5, 2.0 and 4.0 respectively. Experimental results are compared to simulations and time-domain experimental results. Differences between absorption and scattering effects in the frequency-domain are highlighted. Main problems induced by phantom boundaries are presented. Two methods which aim to minimize lateral boundary effects are proposed and tested: the extrapolated lateral-boundary method and the direct polynomial or exponential fitting procedure. With these corrections, we are able to resolve well the two most contrasted inhomogeneities.

Local and superficial optical characterization of biological tissues can be achieved by measuring the spatially resolved diffuse reflectance at small source-detector separations. The sensitivity of the signal to the phase function, absorption and scattering coefficients were studied using Monte Carlo simulations. Measurements of spatially resolved reflectance were performed in vivo on human brain with source-detector separations from 0.3 to 1.5 mm. Distinct optical properties were found between normal cortex, astrocytoma of optic nerve and normal optic nerve.

Monte Carlo simulations or, to a lesser degree of accuracy, the resolution of the diffusion are generally considered as giving reasonable evaluations of the photon irradiance in tissues, globally described by the radiative transport theory. They are frequently used to calculate the Point Spread Function (PSF) describing the sharpness of transillumination images, resolved either in time or in frequency domain. The PSF is itself completely determined, for an homogenous slab of tissue and in the approximation of the diffusion equation, by the reduced scattering and absorption coefficients: µs' and µa respectively. For some tissue preparations, precise measurements of the PSF show, however, significant discrepancies between the predictions from µs′ and µa and the measured PSF. The propagation of light in biological tissues has been studied both theoretically by Monte Carlo simulations and experimentally in vitro on bovine and porcine liver, fat emulsions, human breast and brain tissues. Absorption and reduced scattering coefficients have been obtained and assessed by matching both the spatial and temporal profiles of a pulsed, collimated light beam to the experimental data. Measurements on fat emulsions and liver exhibit an excellent agreement between the predictions of the radiative transport theory for both spatial and temporal profiles. On the contrary, the spatial profile measured on adipose, breast and brain tissues are systematically too large to be predicted by the radiative transport theory in homogenous tissues. The tissue structure, in particular, the tissue micro and macroheterogeneities and possible site percolation in the model of light transport, not yet evidenced experimentally, could explain the unexpected broadening of the PSF in transillumination images through some tissues like adipose and brain .

We present a method that uses a single Monte Carlo simulation (modeling the light distribution in a turbid media) to obtain a set of results for different optical coefficients. This approach eliminates the repetition of simulations for each different parameter. It is based on an adequate formulation of the radiance, expressed as a function of two probability distributions. The first depends only on the phase function and the geometry, while the second one depends only on the optical coefficients. This procedure requires the storage of the number of collisions and the total pathlength of each photon. An example of the applicability of this method is shown, for which an important spare of computer time has been achieved. The main drawback of the method is a loss of convergence which limits its applicability. This effect is discussed as a function of the optical coefficients.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The resolution of transillumination images is improved by time gating. Theoretically, the point spread function can be made as small as desired by shortening sufficiently the time gate. This assertion does not imply that any small object can be made visible by shortening the time gate. Indeed the noise is a limiting factor to detect objects embedded in scattering medium. The noise has been measured experimentally as a function of the time gate. Experiments have been performed on formaldehyde fixed breast tissues (10 mm thick) with a pulsed Ti:sapphire source (200 fs pulses), detected by an ultrafast diode (the resolution of the measuring system is 40 ps). Any biological tissue, even without object such as tumors or haemorrhages, has heterogeneities, the contribution of which can be considered as a noise, called the anatomical noise. The results show that in our experimental conditions, this anatomical noise is predominant on the noise due to the measuring system, at the exception of very small time gate; and it decreases as the time gate increases. This noise will limit the spatial resolution achievable by time gated transillumination.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A method has been developed to evaluate the absorption and reduced scattering coefficients of slabs of turbid materials, biological tissues in particular, with a one step procedure. The biological tissue is transilluminated by a collimated source and the transmitted part of the signal is detected. The spatial intensity profile of the light is collected by a linear CCD. The temporal profile of an ultrashort laser pulse is measured with an ultrafast photodiode. The spatial or temporal profiles are compared to the results of Monte-Carlo simulations in order to predict the absorption and reduced scattering coefficients of the investigated tissue. The validity of our photon migration model has been carefully assessed by experiments on microspheres suspensions, where exact scattering coefficient and the associated phase function have been derived from Mie theory. These results have allowed us to determine the accuracy of the method. The method has been applied to determine locally the optical coefficients of several selected slabs of biological tissues, and the validity of this approach has been verified.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a study of the dynamics of optical contrast agents indocyanine green (ICG) and methylene blue (MB) in an adenocarcinoma rat tumor model. Measurements are conducted with a combined frequency-domain and steady-state optical technique that facilitates rapid measurement of tissue absorption in the 650–1000-nm spectral region. Tumors were also imaged by use of contrast-enhanced magnetic resonance imaging (MRI) and coregistered with the location of the optical probe. The absolute concentrations of contrast agent, oxyhemoglobin, deoxyhemoglobin, and water are measured simultaneously each second for approximately 10 min. The differing tissue uptake kinetics of ICG and MB in these late-stage tumors arise from differences in their effective molecular weights. ICG, because of its binding to plasma proteins, behaves as a macromolecular contrast agent with a low vascular permeability. A compartmental model describing ICG dynamics is used to quantify physiologic parameters related to capillary permeability. In contrast, MB behaves as a small-molecular-weight contrast agent that leaks rapidly from the vasculature into the extravascular, extracellular space, and is sensitive to blood flow and the arterial input function. © 2003 Optical Society of America.

We introduce a novel and efficient method to provide solutions to inverse photon migration problems in heterogeneous turbid media. The method extracts derivative information from a single Monte Carlo simulation to permit the rapid determination of rates of change in the detected photon signal with respect to perturbations in background tissue optical properties. We then feed this derivative information to a nonlinear optimization algorithm to determine the optical properties of the tissue heterogeneity under examination. We demonstrate the use of this approach to solve rapidly a two-region inverse problem of photon migration in the transport regime, for which diffusion-approximation-based approaches are not applicable. © 2001 Optical Society of America.

The spatially resolved reflectance of turbid media is studied at short source–detector separations (approximately one transport mean free path) with Monte Carlo simulations. For such distances we found that the first and second moments of the phase function play a significant role in the reflectance curve, whereas the effect of higher-order moments is weak. Second-order similarity relations are tested and are found efficient at reducing the number of relevant parameters necessary to predict the reflectance. Indeed, only the four following parameters are necessary: the refractive index, the absorption coefficient, the reduced scattering coefficient, and a phase function parameter γ that depends on the first and second moments of the phase function. For media of known γ, the absorption and reduced scattering coefficients can be determined from the intensity and the slope of the log of the reflectance, measured at a single distance. Other empirical properties of the reflectance are derived from the simulations, using short-distance measurements, which provide clues for determining the scattering and absorption properties. In particular, the slope of the square root of the reflectance does not depend on the absorption coefficient but depends on both the reduced scattering coefficient and the phase function parameter γ.

Local and superficial near-infrared (NIR) optical-property characterization of turbid biological tissues can be achieved by measurement of spatially resolved diffuse reflectance at small source-detector separations (

We measure the in-vivo time-dilution curves of contrast agents in a rat tumor model using broadband near-infrared spectroscopy and Gadolinium enhanced MRI. Results indicate differences in kinetics that may be useful for tracking changes in vasculature as a function of tumor status.

A fast spectroscopic system for superficial and local determination of the absorption and scattering properties of tissue (480 to 950 nm) is described. The probe can be used in the working channel of an endoscope. The scattering properties include the reduced scattering coefficient and a parameter of the phase function called gamma, which depends on its first two moments. The inverse problem algorithm is based on the fit of absolute reflectance measurements to cubic B-spline functions derived from the interpolation of a set of Monte Carlo simulations. The algorithm's robustness was tested with simulations altered with various amounts of noise. The method was also assessed on tissue phantoms of known optical properties. Finally, clinical measurements performed endoscopically in vivo in the stomach of human subjects are presented. The absorption and scattering properties were found to be significantly different in the antrum and in the fundus and are correlated with histopathologic observations. The method and the instrument show promise for noninvasive tissue diagnostics of various epithelia.