This PDF file contains the front matter associated with SPIE-OSA Biomedical Optics Proceedings Volume 6629, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Fluorescence diffuse optical tomography is becoming a powerful tool for the investigation of molecular events in small animal studies for new therapeutics developments. Here, the stress is put on the mathematical problem of the tomography, that can be formulated in terms of an estimation of physical parameters appearing as a set of Partial Differential Equations (PDEs). The Finite Element Method has been chosen here to resolve the diffusion equation because it has no restriction considering the geometry or the homogeneity of the system. It is nonetheless well-known to be time and memory consuming, mainly because of the large dimensions of the involved matrices. Our principal objective is to reduce the model in order to speed up the model computation. For that, a new method based on a multiresolution technique is chosen. All the matrices appearing in the discretized version of the PDEs are projected onto an orthonormal wavelet basis, and reduced according to the multiresolution method. With the first order resolution, this compression leads to the reduction of a factor 2x2 of the initial dimension, the inversion of the matrices is approximately 4 times faster. A validation study on a phantom was conducted to evaluate the feasibility of this reduction method.

We describe a new dynamic optical tomography system that is, unlike currently available analog instrumentation, based on digital data-acquisition and filtering techniques. At the heart of this continuous wave instrument is a digital signal processor (DSP) that collects, collates, processes, and filters the digitized data set. A digital lock-in filter that has been designed for this particular application maximizes measurement fidelity. The synchronously-timed processes are controlled by a complex programmable logic device (CPLD) that is also used in conjunction with the DSP to orchestrate data flow. Real-time data rates as high as 140Hz can be achieved. The operation of the system is implemented through a graphical user interface designed with LabVIEW software, Performance analysis shows very low system noise (~600fW RMS noise equivalent power), excellent signal precision (<0.04% - 0.2%) and long-term system stability (<1% over 40 min). A large dynamic range (~195dB) accommodates a wide scope of measurement geometries and tissue types. First experiments on tissue phantoms show that dynamic behavior is accurately captured and spatial location can be correctly tracked using this system.

It is well known that the interaction between coherent monochromatic radiation and a scattering medium induce a speckle phenomenon. The direct exposure of a photographic film, without a lens to the transmitted radiation, gives speckle pattern. The main problem lies in the determination of parameters which can efficiently characterize this pattern and can be correlated with the optical properties of the medium. In this paper, we present a circular statistics approach to differentiate media.

The poor spatial resolution and reproducibility of the images are disadvantages of near infrared topography. The authors proposed the combination of the double-density probe arrangement and the image reconstruction algorithm using a spatial sensitivity profile to improve the spatial resolution and the reproducibility. However, the proposed method was evaluated only by the simplified adult head model. It is uncertain whether the proposed method is effective to the actual head that has complicated structure. In this study, the proposed method is evaluated by the virtual head phantom the 3Dstructure of which is based upon an MRI scan of an adult head. The absorption change the size of which is almost equivalent to the width of the brain gyri was measured by the conventional method and the proposed method to evaluate the spatial resolution of the topographic images obtained by each method. The positions of the probe arrangements are slightly changed and the topographic images of the same brain activation measured by two probe positions are compared to evaluate the reproducibility of the NIR topography. The results indicate that the combination of the double-density probe arrangement and the image reconstruction algorithm using the spatial sensitivity profile can improve both the spatial resolution and the reproducibility of the topographic image of brain activation in the virtual head phantom. However, the uneven thickness of the superficial tissues affects the accuracy of the position of activation in the images.

Diffuse reflective optical measurement is a useful approach for monitoring the oxygen consumption of living tissue such as brain and muscle. To improve the oxygen consumption measurement accuracy, we propose a method for suppressing the near-surface sensitivity. Diffuse reflective light is detected at the aperture used for irradiating the light and is used as a cancellation signal for near-field sensitivity in the conventional measurement scheme. Photon fluence density functions and positional dependences of detected light sensitivity to change in absorbance were simulated. The sensitivity detected at the same position (aperture) as irradiation was significantly high for the near-surface region. With our method, the near-surface sensitivity is reduced by more than 90% while keeping target sensitivity almost constant (only 3% deterioration). The near-surface and deep-field sensitivity was measured with a phantom with light (785 nm) modulated at 1 kHz through an optical fiber bundle. It confirmed suppressed the near-surface sensitivity by subtracting the light detected at the same aperture from the light detected at another aperture.

A novel approach to improve depth selectivity based on time-domain contrast functions is presented. The method was tested with Monte Carlo simulations showing sensitivity to absorption changes of deep inclusions and improved rejection of superficial effects. Preliminary in-vivo measurements were performed on healthy volunteer during a Valsalva maneuver and during finger tapping discriminating brain cortex activation from hemodynamic changes associated to systemic effects in the scalp.

Using multiple lasers in continuous wave diffuse optical tomography has the advantages that scattering and absorption can be distinguished, and that physiological parameters (chromophore concentrations) can be reconstructed. The choice of the laser wavelengths is crucial to ensure a good separability of scattering and chromophores. Current methods to optimize the wavelengths do not consider the sensitivity of the reconstruction result to deviations of extinction coefficients of the chromophores. But since the available absorption spectra for the individual chromophores show significant deviations, it seems to be necessary to take this into account when optimizing the wavelengths. The wavelength optimization approach presented here is an extension of a method of Corlu et al. An additional criterion is introduced, which evaluates the dependence of reconstructed chromophore concentrations on deviations of the absorption coefficients. The wavelengths found by the new approach are compared to those resulting from the original method. Reconstructions of simulated data show the effect of using various spectra for reconstruction with different wavelength sets and illustrate the advantages of the new wavelength sets, leading to less crosstalk between the chromophore concentrations and lower artifacts.

Diffuse optical topography has excellent features as a noninvasive method that provides 2D location information of cortical activity. However, it cannot distinguish the activation depth. We propose an image reconstruction algorithm that suppresses undesirable effects of skin circulation. It comprises a filtering algorithm that extracts target signals from observation data contaminated by disturbing signals and a 2D visualizing process. Computer simulations revealed its excellent performance. We developed a depth selective diffuse optical topography system prototype and performed phantom experiments. Our algorithm significantly suppressed the influence of the disturbing body in the shallow plane with minimal degradation of the target signal.

The sensitivity to collagen may be useful for diagnostic purposes in mammography, as collagen seems to be involved in the development of breast cancer. Moreover, collagen content is expected to be related to breast density (i.e. breast parenchymal pattern) and its quantification could allow the classification of breast type. Thus we have measured the absorption properties of collagen from 610 to 1040 nm. Absorption spectra of breast from healthy volunteers were then interpreted adding collagen to the other absorbers previously considered (i.e. oxy- and deoxyhemoglobin, water, and lipids). A significant amount of collagen, depending on breast type, is estimated to be present and seems to correlate with breast type. Moreover, adding collagen to the fitting procedure affects remarkably the estimated values of blood content and oxygenation. We have also upgraded our time-resolved multi-wavelength optical mammograph, adding a long wavelength (1060 nm) to improve the spectral information and, in particular, the sensitivity to collagen. Breast measurements on volunteers have recently started.

The cell shape and orientation of red blood cells (RBCs) can be influenced by shear rate and osmolarity. Changes in cell shape and cell orientation can be linked to changes in the optical behavior of the cells. The optical parameters, absorption coefficient μ_a, scattering coefficient μ_s, and effective scattering phase function of blood in the spectral range from 250 nm to 1100 nm were investigated dependent on shear rate and osmolarity. Integrating sphere measurements of light transmittance and reflectance in combination with inverse Monte-Carlo simulations were carried out for different wall shear rates between 0 and 1000 s^-1 and osmolarity variations from 225 to 400 mosmol/l. Changes in shear rate and osmolarity could be shown to have significant influences on the optical parameters which can in part be explained by changes in the complex refractive index, cell shape and organization. Spherical forms of RBCs induced by low osmolarity show reduced scattering effects compared to normal RBC biconcave disks shape. Spinocytes, induced by high osmolarity, show the highest scattering effects. Randomly oriented cells exhibited maximum μ_a and μ_s values whereas cell alignment and elongation at high shear rates led to an asymptotical decrease. Moreover a relationship exists between the observed effects and the hemoglobin absorption. It could be shown that 10% changes in osmolarity have a drastic influence on the optical parameters which is of the same order as they appear for 10% Hct and oxygen saturation changes. Flow induced variations of about 10% have less effect on the optical parameters.

Conventionally, the detection and characterization of an optical inhomogeneity embedded in turbid media is dependent on the perturbation of diffuse photon density wave (DPDW) and its noise level, which is defined as the signal-to-noise ratio (SNR). In this study, we calculate the limitation of detection and characterization by using diffuse photon-pairs density wave (DPPDW) which is a novel method in studying turbid media. DPPDW is produced by linear polarized photon-pairs (LPPPs) laser beam which experience multiple-scattering events in turbid media. Meanwhile, the fractional amplitude and phase noise in detecting heterodyne signal determine the detection and characterization of DPPDW in a multiple scattering medium. The amplitude attenuation and phase change of heterodyne signal of DPPDW and their SNR analysis are demonstrated and discussed. As a result, we anticipate that the properties of DPPDW depending upon the degree of spatial coherence (DOC) and the degree of polarization (DOP) of LPPPs in turbid media can result in an improvement on detection and then the perturbation of DPPDW produced by an inhomogeneity embedded in a multiple scattering medium is able to be measured.

Potential of depth resolution of continuous-wave (CW) illumination in diffuse optical imaging is explained. It is known both experimentally and numerically that in CW measurements photons traversing a homogenous, semi-infinite, highly scattering medium between a source and a detector located on the surface of the medium follow paths that the volume interrogated resembles a banana-shape. Also is known that, sensitivity profile of photon propagation in CW measurements is non-uniformly distributed in depth, reaching a maximum at a certain value depending on geometry, source-detector separation, and optical properties of the medium. The presence of an inclusion with a higher absorption coefficient with respect to that of the background in a homogeneous medium can be estimated by increasing time-rate-ofphoton- injection into the medium. The inclusion is assumed to be at a depth between the optode pair such that distances to optodes are the same. An increment in the time-rate-of-photon-injection will give different detection slopes depending on the depth of the inclusion, because the number of photons which is blocked by the inclusion is high if it resides at a depth where the sensitivity profile has a higher value. In this work, preliminary results of Monte-Simulation of light propagation show that measuring slopes of increase in detected light intensity for different interoptode distances are different for extreme case of screen between optodes blocking all photons below a certain depth. Specification of inclusion with this method may enable us to make predictions about the depth and optical properties of the inclusion to be used as a priori information to be used image reconstruction in diffuse optical tomography that may be integrated imaging systems.

In spite of many progresses achieved both with theories and with experiments in studying light propagation through diffusive media, a reliable method for accurate measurements of the optical properties of diffusive media at NIR wavelengths is, in our opinion, still missing. It is therefore difficult to create a reference diffusive medium. We describe two methods in the CW and time domain to calibrate the reduced scattering coefficient of a liquid diffusive medium and the absorption coefficient of an absorber with a standard error smaller than 2% for both the coefficients.

The absorption and reduced scattering coefficients determine the radial dependence of the diffuse reflectance that is due to a point source. A system consisting of a HeNe laser source and a CCD camera was built for making remote measurements of spatially resolved diffuse reflectance. First, liquid tissue phantoms were made of Lipovenös and trypan blue. To determine the optical properties of the tissue phantoms a program code was implemented convolving the pointspread function of the camera with the solution of the diffusion equation and fitting the result to the measured data. We found that the prediction of &mgr;a and &mgr;s' was accurate within ± 10 % and ± 4 %. To check these results also measurements with a multiple fiber-optic detector in contact with the phantom surface at varying distances from the source were accomplished. The intensity signal was measured with twelve low noise photodiodes. We found good agreement between both approaches.

We implemented a two-dimensional finite-difference time-domain (FDTD) method for the calculation of the scattering by turbid slabs containing cylindrical scatterers. We present validation results of the FDTD method used for the calculation of the scattering by an infinite dielectric cylinder. In particular the error caused by numerical dispersion due to an expansion of the simulation grid is discussed. Finally, an analytical solution of the scattering by an infinite cylinder has been used to analyze the error caused by the discrete near- to far-field transformation.

The concentration changes in oxygenated haemoglobin and deoxygenated haemoglobin in the brain cortex of guinea pigs associated with brain activation are measured from the multi-spectral images of the cortical tissue. The cortical tissue is observed through a thinned skull. The wavelength dependence of the optical path length is considered in the calculation of haemoglobin concentration. The results are compared with those obtained from the multi-spectral images of the exposed cortex to evaluate the influence of the thinned skull on the measurement of the concentration changes by multispectral imaging system. Although the skull thickness affected the sensitivity of the change in reflectance due to decrease in optical path in the cortical tissue, the influence of skull on the wavelength dependence of the optical path length can be ignored when the skull thickness is approximately less than 100 &mgr;m.

We have already demonstrated the potentiality of interferometry to perform timeresolved measurements of the light scattered by a tissue: the fluctuations of the speckle pattern, linked to a wavelength-modulation of the source, are registered, and the time-resolved average intensity can be numerically obtained from these data[1]. The competitive results were obtained with a simple photodiode as detector[2]. Such a method can be cheaper and more accessible for biomedical applications than direct time-resolved methods, but it is not its unique advantage: this method allows to perform Diffusing Wave Spectroscopy (DWS) with selected photon pathlengths[3,4]; for instance, we have shown that we can improve the spatial resolution in transillumination imaging of a dynamic heterogeneity through the selection of short photon transit times[4]. Therefore such a method can offer interesting applications, for example in mammography. A way to improve the signal to noise ratio of this method can consist in multiplying the number of detectors. That's the reason why we decide to consider the use of a high speed camera, that can reach a rate of 1000 frames per second. We will present the first results obtained with this new system. The performance will be discussed, and compared to our previous setup.

The anisotropic light propagation in biological tissue is investigated in the steady-state and time domains. Monte Carlo simulations performed for tissue that has anisotropic optical properties show that the steady-state and time-resolved reflectance depends strongly on the measurement direction. We examined the determination of the optical properties using an isotropic diffusion model and found that in the time domain, in contrast to steady-state spatially-resolved reflectance measurements, the obtained absorption coefficient does not depend on the measurement direction and is close to the correct value. We performed measurements of the steady-state and time-resolved reflectance from porcine and bovine tendon which confirmed the theoretical findings. In addition, we compared the results obtained from Monte Carlo simulations with the solutions of the anisotropic diffusion theory for reflectance from semi-infinite media and for transmittance from slabs. In contrast to the literature, we found that the anisotropic diffusion equation is, in general, not a valid approximation to the anisotropic light propagation even in the diffusive regime.

Optical probing of hemodynamics is often employed in areas such as brain, muscular, and breast-cancer imaging. In these studies an external stimulus is applied and changes in relevant physiological parameters, e.g. oxy or deoxyhemoglobin concentrations, are determined. In this work we present the first application of this method for characterizing joint diseases, especially effects of rheumatoid arthritis (RA) in the proximal-interphalangeal (PIP) finger joints. Using a dual-wavelength tomographic imaging system together with previously implemented model-based iterative image reconstruction schemes, we have performed dynamic imaging case studies on a limited number of healthy volunteers and patients diagnosed with RA. Inflating a sphygmomanometer cuff placed around the forearm we elicited a controlled vascular response. We observed pronounced differences between the hemodynamic effect occurring in healthy volunteers and patients affected by RA.

The measurement of skeletal muscle oxygenation by NIRS methods is obstructed by the subcutaneous adipose tissue which might vary between < 1 mm to more than 12 mm in thickness. A new algorithm is developed to minimize the large scattering effect of this lipid layer on the calculation of muscle haemoglobin / myoglobin concentrations. First, we demonstrate by comparison with ultrasound imaging that the optical lipid signal peaking at 930 nm is a good predictor of the adipose tissue thickness (ATT). Second, the algorithm is based on measurements of the wavelength dependence of the slope &Dgr;A/&Dgr;&rgr; of attenuation A with respect to source detector distance &rgr; and Monte Carlo simulations which estimate the muscle absorption coefficient based on this slope and the additional information of the ATT. Third, we illustrate the influence of the wavelength dependent transport scattering coefficient of the new algorithm by using the solution of the diffusion equation for a two-layered turbid medium. This method is tested on experimental data measured on the vastus lateralis muscle of volunteers during an incremental cycling exercise under normal and hypoxic conditions (corresponding to 0, 2000 and 4000 m altitude). The experimental setup uses broad band detection between 700 and 1000 nm at six source-detector distances. We demonstrate that the description of the experimental data as judged by the residual spectrum is significantly improved and the calculated changes in oxygen saturation are markedly different when the ATT correction is included.

In the brain activation measurements by near infrared spectroscopy (NIRS), the partial optical path length in the brain, which is an index of the sensitivity of the NIRS signal to the brain activation, is strongly affected by the thickness and the structure of the superficial tissues. In this study, we investigate the influence of the frontal sinus on the NIRS signal of the brain activation. The light propagation in a simplified head model including a void region mimicking the frontal sinus is predicted by Monte Carlo simulation to investigate the influence of the frontal sinus on the partial optical path length in the brain and the mean optical path length in the head. The frontal sinus strongly affects the light propagation in the head. The partial optical path length for small source-detector separation tends to be increased by the presence of the frontal sinus whereas that for large source-detector separation is decreased by the influence of the frontal sinus.

We have developed a perturbation Monte Carlo method for calculating forward and inverse solutions to the optical tomography imaging problem in the presence of anatomical a priori information. The method uses frequency domain data. In the present work, we consider the problem of imaging hemodynamic changes due to brain activation in the infant brain. We test finite element method and Monte Carlo based implementations using a homogeneous model with the exterior of the domain warped to match digitized points on the skin. With the perturbation Monte Carlo model, we also test a heterogeneous model based on anatomical a priori information derived from a previously recorded infant T1 magnetic resonance (MR) image. Our simulations show that the anatomical information improves the accuracy of reconstructions quite significantly even if the anatomical MR images are based on another infant. This suggests that significant benefits can be obtained by the use of generic infant brain atlas information in near-infrared spectroscopy and optical tomography studies.

Neurological impairments following cardio-pulmonary bypass (CPB) during open heart surgery can result from microembolism and ischaemia. Here we present results from monitoring cerebral haemodynamics during CPB with near infrared spatially resolved broadband spectroscopy. In particular, the study has the objective (a) to monitor oxy- and deoxy-hemoglobin concentrations (oxy-Hb, deoxy-Hb) and their changes as well as oxygen saturation during CPB surgery and (b) to develop and test algorithms for the calculation of these parameters from broad band spectroscopy. For this purpose a detection system was developed based on an especially designed lens imaging spectrograph with optimised sensitivity of recorded reflectance spectra for wavelengths between 600 and 1000 nm. The high f/#-number of 1:1.2 of the system results in about a factor of 10 higher light throughput combined with a lower astigmatism and crosstalk between channels when compared with a commercial mirror spectrometers (f/# = 1:4). For both hemispheres two independent channels each with three source-detector distances (&rgr; = 25 . 35 mm) were used resulting in six spectra. The broad band approach allows to investigate the influence of the wavelength range on the calculated haemoglobin concentrations and their changes and oxygen saturation when the attenuation A(&lgr;) and its slope &Dgr;A(&lgr;)/&Dgr;&rgr; are evaluated. Furthermore, the different depth sensitivities of these measurement parameters are estimated from Monte Carlo simulations and exploited for an optimization of the cerebral signals. It is demonstrated that the system does record cerebral oxygenation parameters during CPB in infants. In particular, the correlation of haemoglobin concentrations with blood supply (flow, pressure) by the heart-lung machine and the significant decreases in oxygen saturation during cardiac arrest is discussed.

The design and fabrication of time-correlated single photon counting (TCSPC) avalanche photodiodes (APDs) and associated quenching circuits have made significant progresses in recent years. APDs with temporal resolutions comparable to microchannel plate photomultiplier tubes (MCP-PMTs) are now available. MCP-PMTs were until these progresses the best TCSPC detectors with timing resolutions down to 30ps. APDs can now achieve these resolutions at a fraction of the cost. Work is under way to make the manufacturing of TCSPC APDs compatible with standard electronics fabrication practices. This should allow to further reduce their cost and render them easier to integrate in complex multi-channel TCSPC electronics, as needed in diffuse optical tomography (DOT) systems. Even if their sensitive area is much smaller than that of the ubiquitous PMT used in TCSPC, we show that with appropriate selection of optical components, TCSPC APDs can be used in time-domain DOT. To support this, we present experimental data and calculations clearly demonstrating that comparable measurements can be obtained with APDs and PMTs. We are, to our knowledge, the first group using APDs in TD DOT, in particular in non-contact TD fluorescence DOT.

We introduce a novel non-contact fluorescence diffuse optical tomography (FDOT) approach for localizing a fluorescent inclusion embedded in a scattering medium. It uses the time of flight of early photons arriving at several detector positions around the medium. It is a true and direct time-of-flight approach in that arrival times are converted to distance. The arrival time of early photons is found via a recently introduced numerical constant fraction discriminator applied to fluoresced photons time-of-flight distributions (fluorescence time pointspread functions (FTPSFs)). Time-correlated single photon counting and an ultrafast photon counting avalanche photodiode are used for measuring FTPSFs that form tomographic data sets. The FDOT localization algorithm proceeds in two steps. The first determines the angular position of the inclusion as the average, over projections, of angular detector positions with smallest arrival time. The second determines the inclusion's radial position based on relative arrival times obtained at several detector positions within each tomographic projection relatively to a reference detector position, the latter being that of shortest arrival time in the projection. The radial position found minimizes the discrepancy between relative arrival times computed for several possible inclusion positions and relative arrival times deduced from experimental data. Two methods are presented for this.

Complete projection (360°) free-space fluorescence tomography of opaque media is poised to enable highly performing three-dimensional imaging through entire small animals in-vivo. This approach can lead to a new generation of Fluorescence Molecular Tomography (FMT) systems since it allows high spatial sampling of photon fields propagating through tissue at any projection, employing non-constricted animal surfaces. Key features of this development is the implementation of non-contact illumination, for example by using beam scanning techniques for light delivery on the tissue surface and direct non-contact imaging with CCD cameras. Similarly, the development of free-space geometries, i.e. implementations that do not utilize immersion of the animal in matching fluids are essential for obtaining appropriate experimental simplicity and avoid unnecessary diffusion through scattering matching media. To facilitate these developments it is important to retrieve the three-dimensional surface and a common coordinate system for the illumination system, the detection system and the animal. Herein, we employ a volume carving method to capture three-dimensional surfaces of diffusive objects from its silhouettes and register the captured surface in the geometry of an FMT 360°-projection acquisition system to obtain three-dimensional fluorescence image reconstructions. Using experimental measurements we evaluate the accuracy of the surface capture procedure by reconstructing the surfaces of phantoms of known dimensions and demonstrate how this surface extraction method can be utilized in an FMT inversion scheme. We then employ this methodology to characterize the animal movement of anaesthetized animals and study the effects of animal movement on the FMT reconstructed image quality.

Small animal diffuse optical tomography is an appealing tool for the investigation of molecular events in cancer research and drug developments. The combination of the functional information brought by an optical system and the anatomical information delivered by X-Rays enables i) a fast multimodality animal examination; ii) the correlation between the biodistribution of the molecular probes and the morphology of the animal; iii) a more accurate optical data reconstructions by using the anatomy of the animal as a constrain in the reconstructions. A small animal multimodality tomographer for the coregistration of fluorescence optical signals and X-rays measurements is used in the present study. The optical system is composed with a CW laser and a CCD camera coupled with an appropriate combination of filters for the fluorescence detection. The animal is placed inside a transparent tube filled with an index matching fluid. The X-ray generator and detector have been positioned perpendicularly to the optical chain. Original optical calibration techniques have been developed in order to control at any time the alignment between the incident beam, the axis of the cylinder and the focus plan of the CCD. Specific developments have also been handled for obtaining the geometry correlation between optical and X-rays data reconstructions. This experimental setup is used in the present work for a study conducted on different kinds of fluorochromes for the purpose of the development of new molecular probes. The instrument is also used for in vivo biological study conducted on mice bearing tumors in the lungs, and tagged with near infrared optical probes (targeting probes such as Transferin- AlexaFluor 750 or such as RAFT-(cRGD)₄-Alexa700/Alexa750).

Optical properties heterogeneities in small-animals can deeply affect diffuse optical fluorescence data. This can severely limit the precision of fluorescence tomography when the forward model is built assuming homogeneous absorption and scattering coefficients. In this work, we introduce a photon propagation forward model in which local estimates of a sample's optical properties are used for each source-detector combination, rather than a single global estimate of those optical properties. These estimates may be obtained from either time-resolved data collected at the laser's wavelength, or based on a priori information gained through another imaging modality. We show that without increasing the computational complexity, our model improves the correlation with independently simulated heterogeneous fluorescence data in the case of optical property heterogeneity levels typically observed in mice.

This paper presents in vivo experiments conducted on cancerous mice bearing mammary murine tumors. In order to reconstruct the fluorescence yield even in highly attenuating and heterogeneous regions like lungs, we developed a fDOT reconstruction method which at first corrects the light propagation model from optical heterogeneities by using the transmitted excitation light measurements. The same approach is also designed to enable working without immersing the mouse in adaptation liquid. The 3D fluorescence map is then reconstructed from the emitted signal of fluorescence and from the corrected propagation model by an ART (Algebraic Reconstruction Technique) algorithm. The system ability to reconstruct fluorescence distribution in presence of high attenuating objects has been validated on phantoms presenting a fluorescent absorbent inclusion. A study was conducted on mice to follow up lungs at different stages of tumor development. The mice were imaged after intravenous injection to the animal of a cancer specific fluorescent marker. A control experiment was conducted in parallel on healthy mice to ensure that the multiple injections of fluorophore did not induce parasite fluorescence distribution. These results validate our system performances for studying small animal lungs tumor evolution. Detection and localization of the fluorophore fixations expresses the tumor development.

Breast cancer dominates cancers in females. This burden on society and the room for improvements in the current practice of mammography have been stimuli for developing new modalities like photoacoustic mammography. At the University of Twente (UT), an instrument had been developed aimed at performing limited area scans on the human breast. This instrument is called the Twente Photoacoustic Mammoscope (PAM). The PAM is based on generating laserinduced ultrasound from absorbing structures in the breast. The heart of the instrument is a flat PVDF based detector matrix comprising 590 active elements. We show the performance characteristics of the ultrasound detector. The exciting source is an Nd:YAG laser operating at 1064 nm with 5 ns pulses. A study protocol was designed to explore the feasibility of using the PAM to detect cancer in the breasts of patients. The protocol was executed at the Medisch Spectrum Twente by using the mammoscope to obtain photoacoustic region-of-interest (ROI) images of the suspect/symptomatic breasts. We compare the photoacoustic images obtained with x-ray mammograms and ultrasound images. We show photoacoustic images of ROI in one case where we attribute high intensity regions to tumor vascularization.

Recent advances in radiotherapy have created the need to develop novel methods for the accurate, three-dimensional assessment of the applied radiation dose during specific radiotherapy plans. Here we present a study based on the use of polymer gel dosimeters in combination with a novel Optical Projection Tomography system, which allows the association of optical properties, namely the attenuation coefficient, to the irradiation dose. Polymer gel dosimeters are polymerized after X-ray irradiation via free radical production during water radiolysis resulting to increased optical opacity as well as change of the nuclear magnetic resonance relaxation times, thus making it possible to study them with both optical and MRI techniques. The optical tomographic system employs a sensitive CCD camera, a rotation stage allowing full 360 degrees rotation and a homogeneous white light source transilluminating the samples. This setup allows the calculation of the optical attenuation coefficient which can then be directly related to the applied radiotherapy dose, as well as the definition of the surface of the sample in space. The experimental procedure involves the recording of transillumination images of the polymer samples in steps of 1 degree to get the desired resolution. Data analysis is performed by back propagating the photons using an inverse Radon transform resulting to the reconstruction of three dimensional images of the attenuation coefficient or equivalently the dose distribution. The sensitivity and dynamic range offered by the technique covers the range of radiotherapy doses in modern clinical practice and are compared with the corresponding achieved with MRI.

Tight autoregulation of vessel tone guarantees proper delivery of nutrients to the tissues. This regulation is maintained at a more delicate level in the brain since any decrease in the supply of glucose and oxygen to neuronal tissues might lead to unrecoverable injury. Functional near infrared spectroscopy has been proposed as a new tool to monitor the cerebrovascular response during cognitive activity. We have observed that during a Stroop task three distinct oscillatory patterns govern the control of the cerebrovascular reactivity: very low frequency (0.02-0.05 Hz), low frequency (0.08-0.12 Hz) and high frequency (0.12-0.18 Hz). High frequency oscillations have been shown to be related to stress level of the subjects. Our findings indicate that as the stress level is increased so does the energy of the high frequency component indicating a higher stimulation from the autonomic nervous system.

Skin behaves as a viscoelastic material, having mechanical properties composed of elastic and fluid components. Upon indentation, the fibres are stretched and fluid displaced from the compressed region. The rate of recovery from this imprint is therefore dependent on the hydration and elasticity of the skin. A reliable measurement could be applied to the assessment of clinical conditions such as oedema, rare genetic disorders such as cutis laxa and the evaluation of the 'effective age' of skin in vivo. This paper describes a new approach to the non-invasive indentation technique and a novel method of analysis. A method is proposed that tracks the skin's recovery optically from an initial strain made using a mechanical indentor, diffuse side-lighting and a CCD video-capture device. Using the blue colour plane of the image it is possible to examine the surface topography only, and track the decay of the imprint over time. Two algorithms are discussed for the extraction of information on the skin's displacement and are analysed in terms of reliability and reproducibility.

Diffuse optical tomography (DOT) is in an attempt to image the interior of human tissues. However, the NIR imaging suffers from low resolution due to the diffusive nature of the scattered light, which results into poor reconstructed image quality. Thus, the effort to improve the image quality remains in progress. The numerical simulation using high-pass filtering incorporated into the finite-element-based diffusion equation to reconstruct tomographic images of optical properties was performed where results reveal that several inclusions (tumors) can be well defined separately, thereby demonstrating the ability to highly resolve the image of interest with the optimal high-pass filtering process.

This paper describes the development of a novel gauging computer vision system for murine non-melanoma skin cancer tumours volume imaging. The system utilized binocular stereovision, enhanced through the use of telecentric lenses. These lenses optically compromised for the distortion factors and provided orthographic projection, leading to parallax free image acquisition. In order to improve the resolution of the system, a structured light projector, with 450 nm dominant wavelength, was used to illuminate the target with a custom pattern. Robust image processing algorithms granted accurate segmentation, feature recognition, labeling and correlation between the stereo pairs. Under these premises, the well-known "matching" problem was resolved successfully and geometrical interpolation provided an accurate three-dimensional reconstruction of the tumour volume. Through back-projection of the calibration object the resolution of the system was calculated up to 0.04 mm. The system was applied to measure the induced geometrical alterations of the tumour after PDT by using the Fosgel photosensitizer, excited by a laser diode emitting at 652 nm. The measurement of the volume induced alterations after each PDT treatment and up to the final tumour shrinkage is critical, to compare PDT efficacy between different protocols.

Near-Infrared (NIR) Diffuse Optical Tomography (DOT) is a non-invasive imaging technique which is used to obtain functional and physiological images of soft tissue, such as the female breast, specifically for the detection and characterization of breast cancer. The vast majority of the work to date has been limited to two dimensional (2D) models which have provided valuable insight into tissue function and physiology enabling a better understanding of tumor development and treatment. Although the 2D image reconstruction approach is fast and computationally efficient, it has limitations as it does not correctly represent the volume under investigation and therefore do not provide the most accurate model for image reconstruction. Three dimensional (3D) modeling and image reconstruction is becoming more accessible through the development of sophisticated numerical models and computationally fast algorithms. A robust and general method is presented which reconstructs 3D functional images using a more accurate and realistic spectral model of 3D light propagation in tissue. Results from a single patient example are presented to demonstrate the clinical importance of 3D image reconstruction in optical tomography for the detection and characterization of breast cancer.

A time-domain NIRS multichannel system was used to monitor hemodynamic changes in the muscle of volunteers and hemiplegic patients during functional electrical stimulation for rehabilitation purposes.

A time-domain fNIRS multichannel system was used in a sustained attention protocol (continuous performance test) to study activation of the prefrontal cortex. Preliminary results on volounteers show significant activation (decrease in deoxy-hemoglobin and increase in oxy-hemoglobin) in both left and right prefrontal cortex.

Fat emulsions like Intralipid are frequently used in research of light propagation in turbid media as tissue phantoms. We investigated the optical properties, the scattering coefficient &mgr;s, the reduced scattering coefficient &mgr;s' and the anisotropy factor g of different major brands and different fat concentrations (10% and 20%) of these fat emulsions in the visible from 450nm to 950nm. The phase function was measured with a goniometrical setup and the anisotropy factor was calculated from this. A collimated transmission setup was used to measure &mgr;s. Significant differences were found between the different brands and between different concentrations of the same brand. We also found significant differences compared to the values published in literature.

Spatial resolved diffuse reflectance signals were obtained by Monte Carlo simulation from a cylindrical vessel filled with a suspension of particles mimicking the nonaggregating erythrocytes. The vessel is embedded in a scattering medium with optical properties close to those of human skin. It is shown that due to strong absorption and scattering properties of the blood, a decrease in reflected radiation is maximal directly over the embedded cylinder. This feature makes the technique potentially useful for imaging and sizing the blood vessels. It is also shown that the image blur increases next to linearly with the increase in blood vessel embedding depth. This feature can be used for determining the latter for the vessels with fixed radii and fixed optical properties of the surrounding medium. The optimal position for the laser probe yielding the highest image quality was found.

Optical tomography of small tissue volumes, as they are encountered in rodent or finger imaging, holds great promise as the signal-to-noise levels are usually high and the spatial resolutions are much better than that of large imaging domains. To accurately model the light propagation in these small domains, radiative transport equations have to be solved directly. In the study at hand, we use the frequency-domain equation of radiative transfer (ERT) to perform a sensitivity study. We determine optimal source-modulation frequencies for which amplitude and phase of the measured signal. These results will be useful in designed experiments and optical tomographic imaging system.

In this paper, we describe a novel clinical breast diffuse optical tomography (DOT) instrument for CW and RF data acquisition in transmission geometry. It is designed to be able to acquire a massive amount of data in a short amount of time available for patient measurement by using a 209-channel galvo-based fast optical switch and a fast electron-multiplying CCD. In addition to CW measurements, RF measurements were made by using an electro-optic modulator for source modulation and a gain-modulated image intensifier for detection. The patient bed has many clinically-oriented features as well as improved data acquisition rate and transmission RF measurement capability. A series of preliminary results will be shown, including a heterodyne RF experiment for bulk property measurement and a CW experiment for 3D imaging. In order to deal with large data size, a linear reconstruction algorithm that exploits separability of the inverse problem in Fourier domain is used for fast and memory-load-free reconstruction.

Near-infrared diffuse optical tomography (NIR DOT) for noninvasive tissue monitoring have been developed for nearly two decades. The NIR imaging, however, suffers from low resolution due to the diffusive nature of the scattered light; there are compelling reasons for merging high-resolution structural information from other imaging modalities with the functional information attainable with NIR DOT. In this article, slight variation of the inclusion (tumor) in low contrast of optical properties is estimated and investigated. We present that an initial study of using a structural a prioriknowledge in NIR tomography where absorption image reconstruction of the tested phantom is well defined with the aid of a structural a priori knowledge obtained from other imaging modalities. This is advantageous compared to either modality alone. As well, the reconstructed optical absorption coefficient is achieved more accurate near to be exact value with incorporating the empirical updating information being proportional to the off-boundary distance but not size of inclusion against the background. Numerical simulation is demonstrated on varied sizes, locations and contrast of the inclusion. With the comparison between with or without a priori and empirical updating information, it is found that the reconstructed optical properties are more accurate than the near-infrared imaging alone.

We report a novel technique to reconstruct fluorescence lifetime distributions in turbid media by using Fourier domain reconstruction of time gated imaging data. The time gating provides sufficient temporal resolution to determine short fluorescence lifetimes while the use of the Fourier transform, which is essential for the time de-convolution of the system of the integral equations employed in the reconstruction, permits a relatively rapid reconstruction of 3-D tomographic data. This approach has been applied experimentally to reconstruct fluorescent lifetime distributions corresponding to phantoms with wells filled with fluorescent dyes embedded inside highly scattering slabs. In practice, the scattering medium can itself be fluorescent and we also suggest a simple iterative technique to account for background autofluorescence, which we have also tested experimentally.

Experimental work has been carried out to extend a recently introduced technique, namely non-invasive optical imaging by speckle ensemble (NOISE), to non-invasively image a structure embedded beneath a 2.5mm thick layer of biological tissue (bacon). This method uses a microlens array and a coherent light source in transmission mode. Image reconstruction is achieved by averaging individual images from selected microlenses, thus reducing the speckle noise created due to the tissue layers. We advance on previous work by use of a more powerful laser source (75mW HeNe) and a higher resolution camera (2048x2048). Further advancement led to the introduction of a rotating ground glass diffuser into the system, which additionally reduced the speckle noise and enhanced the image quality. Leading on from this, an even simpler method of imaging beneath biological tissue is devised using the same setup, but without the microlens array. The principle is the same as the NOISE technique, except instead of taking a spatial average of independent speckle patterns a time average is taken within the exposure time of the CCD camera. Experimental results and comparisons are provided that support the theory.