Homogeneous Tissue Phantoms Research Articles

A Miniature Dual-Fiber Probe for Quantitative Optical Coherence Elastography.

We present a miniaturized dual-fiber OCE probe of 1 mm diameter allowing for robust shear wave elastography. Shear wave velocity is estimated between two optics and hence independent of wave propagation between excitation and imaging. We quantify the wave propagation by evaluating either a single or two measurement points. Particularly, we compare both approaches to ultrasound elastography. Our experimental results demonstrate that quantification of local tissue elasticities is feasible. For homogeneous soft tissue phantoms, we obtain mean deviations of 0.15 ms-1 and 0.02 ms-1 for single-fiber and dual-fiber OCE, respectively. In inhomogeneous phantoms, we measure mean deviations of up to 0.54 ms-1 and 0.03 ms-1 for single-fiber and dual-fiber OCE, respectively. We present a dual-fiber OCE approach that is much more robust in inhomogeneous tissues. Moreover, we demonstrate the feasibility of elasticity quantification in ex-vivo coronary arteries. This study introduces an approach for robust elasticity quantification from within the tissue.

Echo speckle imaging of dynamic processes in soft materials.

We present a laser-speckle imaging technique, termed Echo speckle imaging (ESI), that quantifies the local dynamics in biological tissue and soft materials with a noise level around or below 10% of the measured signal without affecting the spatial resolution. We achieve this through an unconventional speckle beam illumination that creates changing, statistically independent illumination conditions and substantially increases the measurement accuracy. Control experiments for dynamically homogeneous and heterogeneous soft materials and tissue phantoms illustrate the performance of the method. We show that this approach enables us to precision-monitor purely dynamic heterogeneities in turbid soft media with a lateral resolution of 100 µm and better.

Uncertainty measurement of radiomics features against inherent quantum noise in computed tomography imaging.

Quantum noise is a random process in X-ray-based imaging systems. We addressed and measured the uncertainty of radiomics features against this quantum noise in computed tomography (CT) images. A clinical multi-detector CT scanner, two homogeneous phantom sets, and four heterogeneous samples were used. A solid tumor tissue removed from a male BALB/c mouse was included. We the placed phantom sets on the CT scanning table and repeated 20 acquisitions with identical imaging settings. Regions of interest were delineated for feature extraction. Statistical quantities-average, standard deviation, and percentage uncertainty-were calculated from these 20 repeated scans. Percentage uncertainty was used to measure and quantify feature stability against quantum noise. Twelve radiomics features were measured. Random noise was added to study the robustness of machine learning classifiers against feature uncertainty. We found the ranges of percentage uncertainties from homogeneous soft tissue phantoms, homogeneous bone phantoms, and solid tumor tissue to be 0.01-2138%, 0.02-15%, and 0.18-16%, respectively. Overall, it was found that the CT features ShortRunHighGrayLevelEmpha (SRHGE) (0.01-0.18%), ShortRunLowGrayLevelEmpha (SRLGE) (0.01-0.41%), LowGrayLevelRunEmpha (LGRE) (0.01-0.39%), and LongRunLowGrayLevelEmpha (LRLGE) (0.02-0.66%) were the most stable features against the inherent quantum noise. The most unstable features were cluster shade (1-2138%) and max probability (1-16%). The impact of random noise to the prediction accuracy by different machine learning classifiers was found to be between 0 and 12%. Twelve features were used for uncertainty measurements. The upper and lower bounds of percentage uncertainties were determined. The quantum noise effect on machine learning classifiers is model dependent. • Quantum noise is a random process and is intrinsic to X-ray-based imaging systems. This inherent quantum noise creates unpredictable fluctuations in the gray-level intensities of image pixels. Extra cautions and further validations are strongly recommended when unstable radiomics features are selected by a predictive model for disease classification or treatment outcome prognosis. • We addressed and used the statistical quantity of percentage uncertainty to measure the uncertainty of radiomics features against the inherent quantum noise in computed tomography (CT) images. • A clinical multi-detector CT scanner, two homogeneous phantom sets, and four heterogeneous samples were used in the stability measurement. A solid tumor tissue removed from a male BALB/c mouse was included in the heterogeneous sample.

Validation of a coupled electromagnetic and thermal model for estimating temperatures during magnetic nanoparticle hyperthermia

Purpose Alternating magnetic field (AMF) tissue interaction models are generally not validated. Our aim was to develop and validate a coupled electromagnetic and thermal model for estimating temperatures in large organs during magnetic nanoparticle hyperthermia (MNH). Materials and methods Coupled finite element electromagnetic and thermal model validation was performed by comparing the results to experimental data obtained from temperatures measured in homogeneous agar gel phantoms exposed to an AMF at fixed frequency (155 ± 10 kHz). The validated model was applied to a three-dimensional (3D) rabbit liver built from computed tomography (CT) images to investigate the contribution of nanoparticle heating and nonspecific eddy current heating as a function of AMF amplitude. Results Computed temperatures from the model were in excellent agreement with temperatures calculated using the analytical method (error < 1%) and temperatures measured in phantoms (maximum absolute error <2% at each probe location). The 3D rabbit liver model for a fixed concentration of 5 mg Fe/cm3 of tumor revealed a maximum temperature ∼44 °C in tumor and ∼40 °C in liver at AMF amplitude of ∼12 kA/m (peak). Conclusion A validated coupled electromagnetic and thermal model was developed to estimate temperatures due to eddy current heating in homogeneous tissue phantoms. The validated model was successfully used to analyze temperature distribution in complex rabbit liver tumor geometry during MNH. In future, model validation should be extended to heterogeneous tissue phantoms, and include heat sink effects from major blood vessels.

Effect of laser pulse shaping on photoacoustic dosimetry in retinal models.

Photoacoustic sensing can be a powerful technique to obtain real-time feedback of laser energy dose in treatments of biological tissue. However, when laser therapy uses pulses with microsecond duration, they are not optimal for photoacoustic pressure wave generation. This study examines a programmable fiber laser technique using pulse modulation in order to optimize the photoacoustic feedback signal to noise ratio (SNR) in a context where longer laser pulses are employed, such as in selective retinal therapy. We have demonstrated with a homogeneous tissue phantom that this method can yield a greater than seven-fold improvement in SNR over non-modulated square pulses of the same duration and pulse energy. This technique was further investigated for assessment of treatment outcomes in leporine retinal explants by photoacoustic mapping around the cavitation-induced frequency band.

GANPOP: Generative Adversarial Network Prediction of Optical Properties From Single Snapshot Wide-Field Images.

We present a deep learning framework for wide-field, content-aware estimation of absorption and scattering coefficients of tissues, called Generative Adversarial Network Prediction of Optical Properties (GANPOP). Spatial frequency domain imaging is used to obtain ground-truth optical properties at 660 nm from in vivo human hands and feet, freshly resected human esophagectomy samples, and homogeneous tissue phantoms. Images of objects with either flat-field or structured illumination are paired with registered optical property maps and are used to train conditional generative adversarial networks that estimate optical properties from a single input image. We benchmark this approach by comparing GANPOP to a single-snapshot optical property (SSOP) technique, using a normalized mean absolute error (NMAE) metric. In human gastrointestinal specimens, GANPOP with a single structured-light input image estimates the reduced scattering and absorption coefficients with 60% higher accuracy than SSOP while GANPOP with a single flat-field illumination image achieves similar accuracy to SSOP. When applied to both in vivo and ex vivo swine tissues, a GANPOP model trained solely on structured-illumination images of human specimens and phantoms estimates optical properties with approximately 46% improvement over SSOP, indicating adaptability to new, unseen tissue types. Given a training set that appropriately spans the target domain, GANPOP has the potential to enable rapid and accurate wide-field measurements of optical properties.

Monte Carlo assessment of beam deflection and depth dose equivalent variation of a carbon-ion beam in a perpendicular magnetic field

PurposeTo evaluate beam deflection and dose equivalent perturbation of carbon-ion (C-ion) versus depth in a perpendicular magnetic field with the motivation of application to potential future development of MRI-guided carbon therapy. MethodsA therapeutic beamline, a rectangular water phantom (homogeneous) and a multi-layer tissue phantom were simulated by applying the FLUKA Monte Carlo simulation code. The C-ion beam deflection variation against depth inside the water phantom at 100, 220 and 310 MeV/nucleon (MeV/n) was calculated in the presence of 0.5, 1.5 and 3 T magnetic fields. The 220 MeV/n primary ion depth dose equivalent variations induced by a 1.5 T field were calculated inside the homogeneous and multi-layer phantoms. ResultsThe calculated deflections were ranging from 0 to 10.5 mm. The Bragg depth did not change by applying a 1.5 T field to both phantoms under study at 220 MeV/n energy. The dose equivalent in the Bragg depth inside the homogeneous and multi-layer tissue phantoms was found to be reduced by 5.1% and 2.95%, respectively. A dose equivalent reduction of 5.77% in the Bragg depth was obtained when an air layer of 1.8 cm thick was added to the multi-layer phantom. ConclusionDose equivalent perturbation and beam deflection become important at energies above 100 MeV/n, in both phantoms affected by a 1.5 T magnetic field.

Automatic system for optical parameters measurements of biological tissues

In this paper a system allowing execution of automatic measurements of the optical parameters of scattering materials in a efficient and accurate manner is proposed and described. The system is designed especially for measurements of biological tissues including phantoms, which closely imitate optical characteristics of a real tissue. The system has modular construction and is based on ISEL system, luminance and color meter and a computer with worked out dedicated software and user interface. Performed measurements of scattering distribution characteristics for selected materials revealed good accuracy, confirmed by comparative measurements using well-known reference characteristics. Full Text: PDF ReferencesWróbel, M. S., Popov, A. P., Bykov, A. V., Kinnunen, M., Jedrzejewska-Szczerska, M., &amp; Tuchin, V. V. (2015). Measurements of fundamental properties of homogeneous tissue phantoms. Journal of Biomedical Optics CrossRef Wróbel, M. S., Jedrzejewska-Szczerska, M., Galla, S., Piechowski, L., Sawczak, M., Popov, A. P., Cenian, A. (2015). Use of optical skin phantoms for preclinical evaluation of laser efficiency for skin lesion therapy. Journal of Biomedical Optics. CrossRef Jędrzejewska-Szczerska, M., Wróbel, M. S., Galla, S., Popov, A. P., Bykov, A. V., Tuchin, V. V., &amp; Cenian, A. (2015). Investigation of photothermolysis therapy of human skin diseases using optical phantoms. In Proceedings of SPIE - The International Society for Optical Engineering. CrossRef Brown A. M., et al.: Optical material characterization through BSDF measurement and analysis, Proc. of SPIE, Vol. 7792, 2010 CrossRef 4-Axis Controller: iMC-S8. Operating Instruction. ISEL Germany AG, 2012. DirectLink Konica Minolta, Inc. (2005-2013). Chroma meter CS-200. Datasheet. DirectLink Malacara D.: Color Vision and Colorimetry; Theory and Applications, SPIE Press, 2002. DirectLink A. Mazikowski, M. Trojanowski: Measurements of Spectral Spatial Distribution of Scattering Materials for Rear Projection Screens used in Virtual Reality Systems, Metrology and Measurement Systems, 20 (3), pp. 443 - 452, 2013 CrossRef

Tissue motion due to needle deflection.

Various concepts of steerable needles have been developed in order to reduce placement errors during insertions and to enable complex procedures through curved trajectories in minimally invasive surgery. When inserted into soft tissue, motion of the targeted location ahead of the needle tip has to be taken into account for controlling such tools. This paper investigates the motion caused by flexible bending needles in comparison to rigid straight ones when inserted into a homogeneous tissue phantom. A laser based experimental setup is used to measure displacements of the substrate around the needles. Displacements are transformed into the local frame in order to quantify the relative substrate motion. It is shown that the radial contribution of the displacements is higher for bending needles and that this effect increases with higher path curvatures. This motion must be taken into account for controlling steerable needles along curved trajectories to reduce placement errors in applications such as multi-targeting or reinsertions in soft tissue.

WE‐EF‐BRA‐02: A Monte Carlo Study of Macroscopic and Microscopic Dose Descriptors for Kilovoltage Cellular Dosimetry

Purpose:To investigate how doses to cellular (microscopic) targets depend on cell morphology, and how cellular doses relate to doses to bulk tissues and water for 20 to 370 keV photon sources using Monte Carlo (MC) simulations.Methods:Simulation geometries involve cell clusters, single cells, and single nuclear cavities embedded in various healthy and cancerous bulk tissue phantoms. A variety of nucleus and cytoplasm elemental compositions are investigated. Cell and nucleus radii range from 5 to 10 microns and 2 to 9 microns, respectively. Doses to water and bulk tissue cavities are compared to nucleus and cytoplasm doses.Results:Variations in cell dose with simulation geometry are most pronounced for lower energy sources. Nuclear doses are sensitive to the surrounding geometry: the nuclear dose in a multicell model differs from the dose to a cavity of nuclear medium in an otherwise homogeneous bulk tissue phantom by more than 7% at 20 keV. Nuclear doses vary with cell size by up to 20% at 20 keV, with 10% differences persisting up to 90 keV. Bulk tissue and water cavity doses differ from cellular doses by up to 16%. MC results are compared to cavity theory predictions; large and small cavity theories qualitatively predict nuclear doses for energies below and above 50 keV, respectively. Burlin's (1969) intermediate cavity theory best predicts MC results with an average discrepancy of 4%.Conclusion:Cellular doses vary as a function of source energy, subcellular compartment size, elemental composition, and tissue morphology. Neither water nor bulk tissue is an appropriate surrogate for subcellular targets in radiation dosimetry. The influence of microscopic inhomogeneities in the surrounding environment on the nuclear dose and the importance of the nucleus as a target for radiation‐induced cell death emphasizes the potential importance of cellular dosimetry for understanding radiation effects.Funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chairs Program (CRC), and the Ontario Ministry of Training, Colleges and Universities

A Hertzian contact mechanics based formulation to improve ultrasound elastography assessment of uterine cervical tissue stiffness

Clinical practice requires improved techniques to assess human cervical tissue properties, especially at the internal os, or orifice, of the uterine cervix. Ultrasound elastography (UE) holds promise for non-invasively monitoring cervical stiffness throughout pregnancy. However, this technique provides qualitative strain images that cannot be linked to a material property (e.g., Young's modulus) without knowledge of the contact pressure under a rounded transvaginal transducer probe and correction for the resulting non-uniform strain dissipation. One technique to standardize elastogram images incorporates a material of known properties and uses one-dimensional, uniaxial Hooke's law to calculate Young's modulus within the compressed material half-space. However, this method does not account for strain dissipation and the strains that evolve in three-dimensional space. We demonstrate that an analytical approach based on 3D Hertzian contact mechanics provides a reasonable first approximation to correct for UE strain dissipation underneath a round transvaginal transducer probe and thus improves UE-derived estimates of tissue modulus. We validate the proposed analytical solution and evaluate sources of error using a finite element model. As compared to 1D uniaxial Hooke's law, the Hertzian contact-based solution yields significantly improved Young's modulus predictions in three homogeneous gelatin tissue phantoms possessing different moduli. We also demonstrate the feasibility of using this technique to image human cervical tissue, where UE-derived moduli estimations for the uterine cervix anterior lip agreed well with published, experimentally obtained values. Overall, UE with an attached reference standard and a Hertzian contact-based correction holds promise for improving quantitative estimates of cervical tissue modulus.

Measurements of fundamental properties of homogeneous tissue phantoms.

We present the optical measurement techniques used in human skin phantom studies. Their accuracy and the sources of errors in microscopic parameters’ estimation of the produced phantoms are described. We have produced optical phantoms for the purpose of simulating human skin tissue at the wavelength of 930 nm. Optical coherence tomography was used to measure the thickness and surface roughness and to detect the internal inhomogeneities. A more detailed study of phantom surface roughness was carried out with the optical profilometer. Reflectance, transmittance, and collimated transmittance of phantoms were measured using an integrating-sphere spectrometer setup. The scattering and absorption coefficients were calculated with the inverse adding-doubling method. The reduced scattering coefficient at 930 nm was found to be 1.57±0.14 mm(−1) and the absorption was 0.22±0.03 mm(−1) . The retrieved optical properties of phantoms are in agreement with the data found in the literature for real human tissues.

Multi-channel medical device for time domain functional near infrared spectroscopy based on wavelength space multiplexing

We have designed a compact dual wavelength (687 nm, 826 nm) multi-channel (16 sources, 8 detectors) medical device for muscle and brain imaging based on time domain functional near infrared spectroscopy. The system employs the wavelength space multiplexing approach to reduce wavelength cross-talk and increase signal-to-noise ratio. System performances have been tested on homogeneous and heterogeneous tissue phantoms following specifically designed protocols for photon migration instruments. Preliminary in vivo measurements have been performed to validate the instrument capability to monitor hemodynamic parameters changes in the arm muscle during arterial occlusion and in the adult head during a motor task experiment.

A CMOS Sensor for Measurement of Cerebral Optical Coefficients Using Non-Invasive Frequency Domain Near Infrared Spectroscopy

A heterodyned architecture is integrated with a 180 nm CMOS chip for use in portable frequency domain near infrared spectroscopy (fdNIRS) tools for real time monitoring of tissue oxygenation in the brain. The design and performance measurement results of this chip are summarized in this paper to demonstrate its applicability in multi-distance fdNIRS to measure the absorption and scattering coefficients of tissue. The 2.25 mm2 chip is integrated with four sensor channels, which have a high frequency low noise front end and information processing circuitry to interface with an avalanche photodiode to detect the high speed weak light signal. The four-channel sensor draws 40 mA of current from a 1.8 V power supply and uses an off-chip counter implemented on an FPGA to quantify the amplitude and phase information required for tissue characterization with and linearity error, respectively. An experiment using the multi-distance measurement is used to measure the optical properties of a homogeneous tissue phantom using the CMOS integrated instrument.

Anti-biofouling conducting polymer nanoparticles as a label-free optical contrast agent for high resolution subsurface biomedical imaging

Optical coherence tomography (OCT) is a modern high resolution subsurface medical imaging technique. Herein we describe: (i) the synthesis of a thiophene-functionalized oligo(ethylene glycol) methacrylate (OEGMA)-based statistical copolymer, denoted poly(2TMOI–OEGMA); (ii) the preparation of sterically-stabilized polypyrrole (PPy) nanoparticles of approximately 60 nm diameter; (iii) the evaluation of these nanoparticles as a NIR-absorbing optical contrast agent for high-resolution OCT imaging. We show that poly(2TMOI–OEGMA)-stabilized PPy nanoparticles exhibit similar optical properties to poly(vinyl alcohol) (PVA)-stabilized PPy nanoparticles of comparable size prepared using commercially available PVA. Spectroscopic measurements and Mie calculations indicate that both types of PPy nanoparticles strongly absorb NIR radiation above 1000 nm, suggesting their potential use as OCT contrast agents. In vitro OCT studies indicate that both types of PPy nanoparticles reduce NIR backscattering within homogeneous intralipid tissue phantoms, offering almost identical contrast performance in this medium. However, PVA-stabilized PPy nanoparticles became colloidally unstable when dispersed in physiological buffer and immersed in a solid biotissue phantom and hence failed to generate a strong contrast effect. In contrast, the poly(2TMOI–OEGMA)-stabilized PPy nanoparticles remained well-dispersed and hence exhibited a strong rapid onset contrast effect within the biotissue phantom under identical physiological conditions. Ex vivo studies performed on excised chicken and porcine skin tissue demonstrated that topical administration of a low concentration of poly(2TMOI–OEGMA)-stabilized PPy nanoparticles rapidly enhances OCT image contrast in both cases, allowing key tissue features to be readily identified.

SU‐E‐T‐373: The Comparative Research of Monte Carlo Simulation Based Inhomogeneous Tissue Correction Algorithm

Purpose: Two kinds of improved Batho method are proposed in this paper, the dose correction results for test example are compared also.Method and Materials:[Method1].The MC simulation model is : a 1cm3 cavity is placed in the central axis of 30cm3 water phantom. The center of the cavity is (0,0,0.5),'¦(0,0,29.5). The dose distribution of the cavity is simulated, the relative error with homogeneous water phantom is obtained and pre‐treated by the relative error databases. The corrected dose distribution is got in two steps, the cavity region and boundary point are corrected corresponding to the relative error databases firstly, then, the inhomogeneous tissue outside the cavity is corrected according to the Batho method.[Method2].The density of human tissue is divided into four corresponding intervals in terms of the value of CT. The simulation model is: a 1 cm3 typical inhomogeneous tissue is placed at the central axis of 30 cm3 homogeneous tissue phantom. Compared with the PDD of pure homogeneous tissue phantom, the relative error database can be obtained. The program judges the destiny change along the primary ray path. The Batho algorithm is used for dose correction when the destiny of tissue is relatively uniform. In the inhomogeneous interface between different tissues and inside cavity, the program will quickly find the relative error by index according to tissue density changes and depth, read the corresponding data to gain accurate correction results. Results: The method 1 obtain better correction result in the boundary point compared to MC simulation, but, in the cavity, the maximum error correction is 9.661%. Accordingly, the maximum correction error in the cavity region by method2 is 4.73%, in the boundary point is 2.47%, can satisfy the clinical precision requirement of 5%. Conclusions: The method 2 can obtain satisfactory correction Result in inhomogeneous tissue interface and the cavity area. The work is supported by the National Natural Science Foundation of China (60872112 and 10805012), the Natural Science Foundation of Anhui Province (11040606M132) and the Fundamental Research Funds for the Central Universities and the Science Research and Development Fund of Hefei University of Technology (2012HGXJ0062).

Toward soft-tissue elastography using digital holography to monitor surface acoustic waves

Measuring the elasticity distribution inside the human body is of great interest because elastic abnormalities can serve as indicators of several diseases. We present a method for mapping elasticity inside soft tissues by imaging surface acoustic waves (SAWs) with digital holographic interferometry. With this method, we show that SAWs are consistent with Rayleigh waves, with velocities proportional to the square root of the elastic modulus greater than 2-40 kPa in homogeneous tissue phantoms. In two-layer phantoms, the SAW velocity transitions approximately from that of the lower layer to that of the upper layer as frequency is increased in agreement with the theoretical relationship between SAW dispersion and the depth-dependent stiffness profile. We also observed deformation in the propagation direction of SAWs above a stiff inclusion placed 8 mm below the surface. These findings demonstrate the potential for quantitative digital holography-based elastography of soft tissues as a noninvasive method for disease detection.

Performance of Two Dimensional Displacement and Strain Estimation Techniques Using a Phased Array Transducer

The goal of this study was to investigate the applicability of conventional 2-D displacement and strain imaging techniques to phased array radiofrequency (RF) data. Furthermore, the possible advantages of aligning and stretching techniques for the reduction of decorrelation artefacts was examined. Data from both realistic simulations and phantoms were used in this study. Recently, the used processing concepts were successfully applied to linear array data. However, their applicability to sector scan data is not trivial because of the polar grid. Homogeneous and inhomogeneous tissue phantoms were simulated at a range of strains (0 to 5%) using Field II ©. The inhomogeneous phantom, a commonly used tumor/lesion model, was also constructed using gelatin/agar solutions. A coarse-to-fine displacement algorithm was applied, using aligning and stretching to enhance re-correlation. Vertical and horizontal strains were reconstructed from the axial and lateral displacements. Results revealed that the error on displacement estimates was lower when using 2-D data windows rather than 1-D windows. For regions at large depths and large insonification angles, the allowed lateral window size was limited. Still, 1-D windows resulted in larger errors. The re-correlation techniques resulted in a significant increase in the elastographic signal-to-noise ratio (SNRe) and elastographic contrast-to-noise ratio (CNRe) of the vertical and horizontal strain components. An increase of the SNRe of 5–20 dB was observed over a range of strains (0.5 to 5.0%). In the inhomogeneous phantom, a vertical SNRe of 27.7 dB and a horizontal SNRe of 16.7 dB were measured in the background. The vertical and horizontal CNRe were 35 dB and 23.1 dB, respectively. For the experimental data, lower SNRe (vertical: 19.1 dB; horizontal: 11.4 dB) and CNRe (vertical: 33.3 dB; horizontal: 12.5 dB) were found. In conclusion, 2-D window matching of sector scan data is feasible and outperforms 1-D window matching. Furthermore, the use of re-correlation techniques enhances both precision and contrast of strain images. (E-mail: r.lopata@cukz.umcn.nl)

Time-Resolved Diffuse Reflectance Using Small Source-Detector Separation and Fast Single-Photon Gating

We demonstrate the feasibility of time-resolved diffuse reflectance measurements at small source-detector separations using a single-photon avalanche diode operated in time-gated mode. Photon time distributions at an interfiber distance of 2 mm were obtained on a homogeneous tissue phantom with a dynamic range of 10(6) and collecting photons at arrival times up to 4 ns. Moreover, we were able to detect a local inhomogeneity deeply buried within a diffusive medium with better spatial resolution, higher signal intensity, and same contrast of a larger (20 mm) interfiber distance. Finally, the proposed approach proved valuable to detect in vivo a task-related brain activation.

Angle-resolved Optical Coherence Tomography with sequential angular selectivity for speckle reduction

We present a novel method for rapidly acquiring optical coherence tomography (OCT) images at multiple backscattering angles. By angularly compounding these images, high levels of speckle reduction were achieved. Signal-to-noise ratio (SNR) improvements of 3.4 dB were obtained from a homogeneous tissue phantom, which was in good agreement with the predictions of a statistical model of speckle that incorporated the optical parameters of the imaging system. In addition, the fast acquisition rate of the system (10 kHz A-line repetition rate) allowed angular compounding to be performed in vivo without significant motion artifacts. Speckle-reduced OCT images of human dermis show greatly improved delineation of tissue microstructure.