Showing papers on "Optical tomography published in 2010"
TL;DR: A linear model for using received signal strength (RSS) measurements to obtain images of moving objects and mean-squared error bounds on image accuracy are derived, which are used to calculate the accuracy of an RTI system for a given node geometry.
Abstract: Radio Tomographic Imaging (RTI) is an emerging technology for imaging the attenuation caused by physical objects in wireless networks. This paper presents a linear model for using received signal strength (RSS) measurements to obtain images of moving objects. Noise models are investigated based on real measurements of a deployed RTI system. Mean-squared error (MSE) bounds on image accuracy are derived, which are used to calculate the accuracy of an RTI system for a given node geometry. The ill-posedness of RTI is discussed, and Tikhonov regularization is used to derive an image estimator. Experimental results of an RTI experiment with 28 nodes deployed around a 441 square foot area are presented.
838 citations
TL;DR: Experimental results show significant differences among measurements from different skin sites, between directions parallel and orthogonal to Langer's lines, and under different skin hydration states, and suggest surface waves with different driving frequencies represent skin biomechanical properties from different layers in depth.
Abstract: Dynamic optical coherence elastography is used to determine in vivo skin biomechanical properties based on mechanical surface wave propagation. Quantitative Young's moduli are measured on human skin from different sites, orientations, and frequencies. Skin thicknesses, including measurements from different layers, are also measured simultaneously. Experimental results show significant differences among measurements from different skin sites, between directions parallel and orthogonal to Langer's lines, and under different skin hydration states. Results also suggest surface waves with different driving frequencies represent skin biomechanical properties from different layers in depth. With features such as micrometer-scale resolution, noninvasive imaging, and real-time processing from the optical coherence tomography technology, this optical measurement technique has great potential for measuring skin biomechanical properties in dermatology.
408 citations
TL;DR: This work focuses on the current state of microvascular imaging and characterization based on photoacoustics, and discusses the methods used to characterize important functional parameters, such as total hemoglobin concentration, hemoglobin oxygen saturation, and blood flow.
Abstract: Photoacoustic (optoacoustic) tomography, combining optical absorption contrast and highly scalable spatial resolution (from micrometer optical resolution to millimeter acoustic resolution), has broken through the fundamental penetration limit of optical ballistic imaging modalities-including confocal microscopy, two-photon microscopy, and optical coherence tomography-and has achieved high spatial resolution at depths down to the diffusive regime. Optical absorption contrast is highly desirable for microvascular imaging and characterization because of the presence of endogenous strongly light-absorbing hemoglobin. We focus on the current state of microvascular imaging and characterization based on photoacoustics. We first review the three major embodiments of photoacoustic tomography: microscopy, computed tomography, and endoscopy. We then discuss the methods used to characterize important functional parameters, such as total hemoglobin concentration, hemoglobin oxygen saturation, and blood flow. Next, we highlight a few representative applications in microvascular-related physiological and pathophysiological research, including hemodynamic monitoring, chronic imaging, tumor-vascular interaction, and neurovascular coupling. Finally, several potential technical advances toward clinical applications are suggested, and a few technical challenges in contrast enhancement and fluence compensation are summarized.
377 citations
TL;DR: A fast model-based inversion algorithm for quantitative 2-D and 3-D optoacoustic tomography based on an accurate and efficient forward model, which eliminates the need for regularization in the inversion process while providing modeling flexibility essential for quantitative image formation.
Abstract: We present a fast model-based inversion algorithm for quantitative 2-D and 3-D optoacoustic tomography. The algorithm is based on an accurate and efficient forward model, which eliminates the need for regularization in the inversion process while providing modeling flexibility essential for quantitative image formation. The resulting image-reconstruction method eliminates stability problems encountered in previously published model-based techniques and, thus, enables performing image reconstruction in real time. Our model-based framework offers a generalization of the forward solution to more comprehensive optoacoustic propagation models, such as including detector frequency response, without changing the inversion procedure. The reconstruction speed and other algorithmic performances are demonstrated using numerical simulation studies and experimentally on tissue-mimicking optically heterogeneous phantoms and small animals. In the experimental examples, the model-based reconstructions manifested correctly the effect of light attenuation through the objects and did not suffer from the artifacts which usually afflict the commonly used filtered backprojection algorithms, such as negative absorption values.
293 citations
TL;DR: This work presents a framework to enable systematic and automatic classification of atherosclerotic plaque constituents, based on the optical attenuation coefficient mu(t) of the tissue, and successfully applies the algorithm to OCT patient data.
Abstract: Optical coherence tomography OCT is rap- idly becoming the method of choice for assessing arterial wall pathology in vivo. Atherosclerotic plaques can be di- agnosed with high accuracy, including measurement of the thickness of fibrous caps, enabling an assessment of the risk of rupture. While the OCT image presents mor- phological information in highly resolved detail, it relies on interpretation of the images by trained readers for the identification of vessel wall components and tissue type. We present a framework to enable systematic and auto- matic classification of atherosclerotic plaque constituents, based on the optical attenuation coefficient t of the tis- sue. OCT images of 65 coronary artery segments in vitro, obtained from 14 vessels harvested at autopsy, are ana- lyzed and correlated with histology. Vessel wall compo- nents can be distinguished based on their optical proper- ties: necrotic core and macrophage infiltration exhibit strong attenuation, t10 mm 1 , while calcific and fi- brous tissue have a lower t25mm 1 . The algorithm is successfully applied to OCT patient data, demonstrating that the analysis can be used in a clinical setting and assist diagnostics of vessel wall pathology. © 2010 Society of Photo-
220 citations
TL;DR: In this article, the authors adapt compressed sensing (CS) for the reconstruction in photoacoustic computed tomography (PACT), which can effectively accelerate the data acquisition and reduce the system cost.
Abstract: The data acquisition speed in photoacoustic computed tomography (PACT) is limited by the laser repetition rate and the number of parallel ultrasound detecting channels. Reconstructing an image with fewer measurements can effectively accelerate the data acquisition and reduce the system cost. We adapt compressed sensing (CS) for the reconstruction in PACT. CS-based PACT is implemented as a nonlinear conjugate gradient descent algorithm and tested with both phantom and in vivo experiments.
170 citations
TL;DR: This technique is based on the idea of characterizing the Fourier spectrum of the multibaseline data as being constituted by two effective scattering centers displaced along the vertical direction, plus the associated decorrelation terms.
Abstract: In this paper, a technique is described for the tomographic characterization of forested areas through multiple synthetic aperture radar (SAR) observations, based on either single or multipolarimetric acquisitions. This technique is based on the idea of characterizing the Fourier spectrum of the multibaseline data as being constituted by two effective scattering centers displaced along the vertical direction, plus the associated decorrelation terms. As a result, SAR tomography will be formulated as the problem of detecting the number of scattering centers within the resolution cell, estimating the parameters that describe their spatial structure, and evaluating the associated backscattered powers. Parameter estimation is carried out through the covariance matching estimation technique, which provides an asymptotically optimal solution. The results of an experiment performed on a real P-band multibaseline fully polarimetric data set relative to the forested site of Remningstorp, Sweden, are reported.
157 citations
TL;DR: The use of Doppler variance (standard deviation) imaging for 3-D in vivo angiography in the human eye is demonstrated, using the variance of blood flow velocity to map the retina and choroid vessels.
Abstract: We demonstrate the use of Doppler variance (standard deviation) imaging for 3-D in vivo angiography in the human eye. In addition to the regular optical Doppler tomography velocity and structural images, we use the variance of blood flow velocity to map the retina and choroid vessels. Variance imaging is subject to bulk motion artifacts as in phase-resolved Doppler imaging, and a histogram-based method is proposed for bulk-motion correction in variance imaging. Experiments were performed to demonstrate the effectiveness of the proposed method for 3-D vasculature imaging of human retina and choroid.
141 citations
TL;DR: It is demonstrated that HD-DOT enables detailed phase-encoded retinotopic mapping, while sparse arrays are limited to imaging individual block-design visual stimuli and that these improvements provide a substantial advancement in neuroimaging capability.
Abstract: Despite the unique brain imaging capabilities and advantages of functional near-infrared spectroscopy (fNIRS), including portability and comprehensive hemodynamic measurement, widespread acceptance in the neuroimaging community has been hampered by low spatial resolution and image localization errors. While recent technical developments such as high-density diffuse optical tomography (HD-DOT) have, in principle, been shown to have superior in silico image quality, the majority of optical imaging studies are still conducted with sparse fNIRS arrays, perhaps partially because the performance increases of HD-DOT appear incremental. Without a quantitative comparative analysis between HD-DOT and fNIRS, using both simulation and in vivo neuroimaging, the implications of the new HD-DOT technology have been difficult to judge. We present a quantitative comparison of HD-DOT and two commonly used fNIRS geometries using (1) standard metrics of image quality, (2) simulated brain mapping tasks, and (3) in vivo visual cortex mapping results in adult humans. The results show that better resolution and lower positional errors are achieved with HD-DOT and that these improvements provide a substantial advancement in neuroimaging capability. In particular, we demonstrate that HD-DOT enables detailed phase-encoded retinotopic mapping, while sparse arrays are limited to imaging individual block-design visual stimuli.
134 citations
TL;DR: The design and characterization of silicone elastomer-based optical phantoms are presented, which are easy to make, based on affordable materials, exhibit well-defined and controllable thickness, refractive index, absorption, and scattering coefficients, are homogeneous, and allow the incorporation of novel types of nanoparticle contrast agents.
Abstract: Current innovations in optical imaging, measurement tech- niques, and data analysis algorithms express the need for reliable test- ing and comparison methods. We present the design and character- ization of silicone elastomer-based optical phantoms. Absorption is included by adding a green dye and scattering by adding TiO2 or SiO2 particles. Optical coherence tomography measurements demon- strate a linear dependence of the attenuation coefficient with scatterer concentration in the absence of absorbers. Optical transmission spec- troscopy of the nonscattering absorbing phantoms shows a linear con- centration dependent absorption coefficient. Both types of samples are stable over a period of 6 months. Confocal microscopy of the samples demonstrates a homogeneous distribution of the scatterers, albeit with some clustering. Based on layers with thicknesses as small as 50 m, we make multifaceted structures resembling flow channels, wavy skin-like structures, and a layered and curved phantom resem- bling the human retina. Finally, we demonstrate the ability to incor- porate gold nanoparticles within the phantoms. In conclusion, our phantoms are easy to make, are based on affordable materials, exhibit well-defined and controllable thickness, refractive index, absorption, and scattering coefficients, are homogeneous, and allow the incorpo- ration of novel types of nanoparticle contrast agents. We believe our phantoms fulfill many of the requirements for an "ideal" tissue phan- tom, and will be particularly suited for novel optical coherence to- mography applications. © 2010 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.3369003
133 citations
TL;DR: The hemodynamics within the entire cerebral cortex of a mouse were studied by using photoacoustic tomography (PAT) in real time to demonstrate that PAT is a powerful imaging modality that can be potentially used to study small animal neurofunctional activities.
Abstract: For the first time, the hemodynamics within the entire cerebral cortex of a mouse were studied by using photoacoustic tomography (PAT) in real time. The PAT system, based on a 512-element full-ring ultrasound array, received photoacoustic signals primarily from a slice of 2-mm thickness. This system can provide high-resolution brain vasculature images. We also monitored the fast wash-in process of a photoacoustic contrast agent in the mouse brain. Our results demonstrated that PAT is a powerful imaging modality that can be potentially used to study small animal neurofunctional activities.
TL;DR: It is demonstrated that the PSOCT system is feasible to image the meaningful vibration of cellular compartments within the OC with an unprecedented sensitivity down to ∼0.5 Å.
Abstract: Hearing loss can mean severe impairment to the quality of life. However, the biomechanical mechanisms of how the hearing organ, i.e., the organ of Corti OC, responds to sound are still elusive, largely because there is currently no means available to image the 3-D motion characteristics of the OC. We present a novel use of the phase-sensitive spectral domain optical coherence tomography PSOCT to characterize the motion of cellular compartments within the OC at a subnanometer scale. The PSOCT system operates at 1310 nm with a spatial resolution of 16 m and an imaging speed of 47,000 A-lines/s. The phase changes of the spectral interferograms induced by the localized tissue motion are used to quantify the vibra- tion magnitude. Fourier transform analysis of the phase changes im- proves the system sensitivity to sense minute vibrations smaller than 1n m. We demonstrate that the PSOCT system is feasible to image the meaningful vibration of cellular compartments within the OC with an unprecedented sensitivity down to 0.5 A. © 2010 Society of Photo-Optical
TL;DR: Through the use of a random noise removal algorithm, the image quality of the reconstructions can be considerably improved even when the noise is strongly present in the acquired projections, suggesting its implementation as an efficient alternative to other filtering schemes such as for example the median filter.
Abstract: Absorption and emission optical projection tomography (OPT), alternatively referred to as optical computed tomography (optical-CT) and optical-emission computed tomography (optical-ECT), are recently developed three-dimensional imaging techniques with value for developmental biology and ex vivo gene expression studies. The techniques' principles are similar to the ones used for x-ray computed tomography and are based on the approximation of negligible light scattering in optically cleared samples. The optical clearing is achieved by a chemical procedure which aims at substituting the cellular fluids within the sample with a cell membranes' index matching solution. Once cleared the sample presents very low scattering and is then illuminated with a light collimated beam whose intensity is captured in transillumination mode by a CCD camera. Different projection images of the sample are subsequently obtained over a 360° full rotation, and a standard backprojection algorithm can be used in a similar fashion as for x-ray tomography in order to obtain absorption maps. Because not all biological samples present significant absorption contrast, it is not always possible to obtain projections with a good signal-to-noise ratio, a condition necessary to achieve high-quality tomographic reconstructions. Such is the case for example, for early stage's embryos. In this work we demonstrate how, through the use of a random noise removal algorithm, the image quality of the reconstructions can be considerably improved even when the noise is strongly present in the acquired projections. Specifically, we implemented a block matching 3D (BM3D) filter applying it separately on each acquired transillumination projection before performing a complete three-dimensional tomographical reconstruction. To test the efficiency of the adopted filtering scheme, a phantom and a real biological sample were processed. In both cases, the BM3D filter led to a signal-to-noise ratio increment of over 30 dB on severe noise-affected reconstructions revealing original—noise-hidden—image details. These results show the utility of the BM3D approach for OPT under typical conditions of very low light absorption, suggesting its implementation as an efficient alternative to other filtering schemes such as for example the median filter.
TL;DR: A prototype XLCT system is built and imaging in an optically diffusive medium shows that imaging performance is not affected by optical scatter; furthermore, the linear response of the reconstructed images suggests that XLCT is capable of quantitative imaging.
Abstract: X-ray luminescence computed tomography (XLCT) is proposed as a new dual molecular/anatomical imaging modality. XLCT is based on the selective excitation and optical detection of x-ray-excitable nanoparticles. As a proof of concept, we built a prototype XLCT system and imaged near-IR-emitting Gd(2)O(2)S:Eu phosphors in various phantoms. Imaging in an optically diffusive medium shows that imaging performance is not affected by optical scatter; furthermore, the linear response of the reconstructed images suggests that XLCT is capable of quantitative imaging.
TL;DR: A new optical acquisition scheme based on a pair of digital micromirror devices is developed and applied to three-dimensional tomographic imaging of turbid media and high-resolution quantitative volumetric imaging of absorption heterogeneities embedded in optically thick samples is performed.
Abstract: A new optical acquisition scheme based on a pair of digital micromirror devices is developed and applied to three-dimensional tomographic imaging of turbid media. By using pairs of illumination-detection patterns with a single detector, we were able to perform high-resolution quantitative volumetric imaging of absorption heterogeneities embedded in optically thick samples. Additionally, a tomographic reconstruction algorithm was implemented on a graphical processor unit to provide optical reconstructions at a frame rate of 2 Hz. The structured illumination method proposed in this work has significant cost advantages over camera systems, as only a single detector is required. This configuration also has the potential to increase frame rate.
TL;DR: In this preliminary study, skin pigmentation had little effect on penetration accomplished at three different wavelengths, and the epidermis and dermal-epidermal junction could be properly delineated using OCT at 800 nm, and this wavelength offered better contrast over the other two wavelength regions.
Abstract: The capability of optical coherence tomography (OCT) to perform "optical biopsy" of tissues within a depth range of 1 to 2 mm with micron-scale resolution in real time makes it a promising biomedical imaging modality for dermatologic applications. Three high-speed, spectrometer-based frequency-domain OCT systems operating at 800 nm (20,000 A-scans/s), 1060 nm, and 1300 nm (both 47,000 A-scans/s) at comparable signal-to-noise ratio (SNR), SNR roll-off with scanning depth, and transverse resolution (<15 µm) were used to acquire 3-D tomograms of glabrous and hairy human skin in vivo. Images obtained using these three systems were compared in terms of penetration depth, resolution, and contrast. Normal as well as abnormal sites like moles and scar tissue were examined. In this preliminary study, skin pigmentation had little effect on penetration accomplished at three different wavelengths. The epidermis and dermal-epidermal junction could be properly delineated using OCT at 800 nm, and this wavelength offered better contrast over the other two wavelength regions. OCT at 1300 nm permits imaging of deeper dermal layers, critical for detecting deeper tumor boundaries and other deeper skin pathologies. The performance at 1060 nm compromises between the other wavelengths in terms of penetration depth and image contrast.
TL;DR: An automatic OCT layer segmentation technique that can be used for computer-aided glaucoma diagnosis is reported that segments layers of OCT images efficiently.
Abstract: Under the framework of computer-aided diagnosis, optical coherence tomography (OCT) has become an established ocular imaging technique that can be used in glaucoma diagnosis by measuring the retinal nerve fiber layer thickness. This letter presents an automated retinal layer segmentation technique for OCT images. In the proposed technique, an OCT image is first cut into multiple vessel and nonvessel sections by the retinal blood vessels that are detected through an iterative polynomial smoothing procedure. The nonvessel sections are then filtered by a bilateral filter and a median filter that suppress the local image noise but keep the global image variation across the retinal layer boundary. Finally, the layer boundaries of the filtered nonvessel sections are detected, which are further classified to different retinal layers to determine the complete retinal layer boundaries. Experiments over OCT for four subjects show that the proposed technique segments an OCT image into five layers accurately.
TL;DR: An l1-regularized multilevel approach for bioluminescence tomography based on radiative transfer equation with the emphasis on improving imaging resolution and reducing computational time is studied.
Abstract: In this paper we study an l1-regularized multilevel approach for bioluminescence tomography based on radiative transfer equation with the emphasis on improving imaging resolution and reducing computational time. Simulations are performed to validate that our algorithms are potential for efficient high-resolution imaging. Besides, we study and compare reconstructions with boundary angular-averaged data, boundary angular-resolved data and internal angular-averaged data respectively.
TL;DR: This work presents high-resolution wide-field imaging of retinal and choroidal blood perfusion with optical microangiography (OMAG) technology, and compares the clinical fluorescein angiography and indocyanine greenAngiography imaging results with the OMAG results of blood perfusions map within the retina andChoroid, and shows excellent agreement between these modalities.
Abstract: We present high-resolution wide-field imaging of retinal and choroidal blood perfusion with optical microangiography (OMAG) technology. Based on spatial frequency analysis, OMAG is capable of visualizing the vascular perfusion map down to capillary-level resolution. An OMAG system operating at 840 nm is used with an A-scan rate of 27,000 Hz, axial resolution of 8 µm, and sensitivity of 98 dB. To achieve wide-field imaging, we capture 16 optical coherence tomography (OCT) 3-D datasets in a sequential order, which together provide an area of ~7.4×7.4 mm2 at the posterior segment of the human eye. For each of these datasets, the bulk tissue motion artifacts are eliminated by applying a phase compensation method based on histogram estimation of bulk motion phases, while the displacements occurring between adjacent B-frames are compensated for by 2-D cross correlation between two adjacent OMAG flow images. The depth-resolved capability of OMAG imaging also provides volumetric information on the ocular circulations. Finally, we compare the clinical fluorescein angiography and indocyanine green angiography imaging results with the OMAG results of blood perfusion map within the retina and choroid, and show excellent agreement between these modalities.
TL;DR: The significant difference in photoacoustic signals between water and fat tissue indicates that the laser-based PAT has the potential to detect water content in tissue.
Abstract: Photoacoustic tomography (PAT) has been widely used to image optically absorptive objects in both human and animal tissues. For the first time, we present imaging of water with laser-based PAT. We photoacoustically measure the absorption spectra of water-ethanol mixtures at various water concentrations, and then image water-ethanol and pure-water inclusions in gel and a water inclusion in fat tissue. The significant difference in photoacoustic signals between water and fat tissue indicates that the laser-based PAT has the potential to detect water content in tissue.
TL;DR: Results demonstrate that OCT imaging of internal fingerprints can be used for accurate and reliable fingerprint recognition.
Abstract: Existing biometric fingerprint devices show numerous reliability problems such as wet or fake fingers. In this letter, a secured method using the internal structures of the finger (papillary layer) for fingerprint identification is presented. With a frequency-domain optical coherence tomography (FD-OCT) system, a 3-D image of a finger is acquired and the information of the internal fingerprint extracted. The right index fingers of 51 individuals were recorded three times. Using a commercial fingerprint identification program, 95% of internal fingerprint images were successfully recognized. These results demonstrate that OCT imaging of internal fingerprints can be used for accurate and reliable fingerprint recognition.
TL;DR: Inclusion of prior information from x-ray CT data in the reconstruction of the fluorescence biodistribution leads to improved agreement between the reconstruction and validation images for both simulated and experimental data.
Abstract: Purpose:
The performance is studied of two newly introduced and previously suggested methods that incorporate priors into inversion schemes associated with data from a recently developed hybrid x-ray computed tomography and fluorescence molecular tomography system, the latter based on CCD camera photon detection. The unique data set studied attains accurately registered data of high spatially sampled photon fields propagating through tissue along 360° projections.
Methods:
Approaches that incorporate structural prior information were included in the inverse problem by adding a penalty term to the minimization function utilized for image reconstructions. Results were compared as to their performance with simulated and experimental data from a lung inflammation animal model and against the inversions achieved when not using priors.
Results:
The importance of using priors over stand-alone inversions is also showcased with high spatial sampling simulated and experimental data. The approach of optimal performance in resolving fluorescent biodistribution in small animals is also discussed.
Conclusions:
Inclusion of prior information from x-ray CT data in the reconstruction of the fluorescence biodistribution leads to improved agreement between the reconstruction and validation images for both simulated and experimental data.
TL;DR: Simulations are performed to show that this approach is not only capable of preserving shapes, details and intensities of bioluminescent sources in the presence of sparse or non-sparse sources with angular-resolved or angular-averaged data, but also robust to noise, and thus is potential for efficient high-resolution imaging with only boundary data.
Abstract: In this paper we study the regularization with both l1 and total-variation norm for bioluminescence tomography based on radiative transfer equation, compare l1 data fidelity with l2 data fidelity for different type of noise, and propose novel interior-point methods for solving related optimization problems. Simulations are performed to show that our approach is not only capable of preserving shapes, details and intensities of bioluminescent sources in the presence of sparse or non-sparse sources with angular-resolved or angular-averaged data, but also robust to noise, and thus is potential for efficient high-resolution imaging with only boundary data.
TL;DR: This study characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser and reports a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier.
Abstract: Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier.
TL;DR: This study demonstrates the feasibility of an OCT-US system for intravascular imaging, which is expected to have a prominent impact on early detection and characterization of atherosclerosis.
Abstract: We report on a dual-modality optical coherence tomography (OCT) ultrasound (US) system for intravascular imaging. To the best of our knowledge, we have developed the first integrated OCT-US probe that combines OCT optical components with an US transducer. The OCT optical components mainly consist of a single-mode fiber, a gradient index lens for light-beam focusing, and a right-angled prism for reflecting light into biological tissue. A 40-MHz piezoelectric transducer (PZT-5H) side-viewing US transducer was fabricated to obtain the US image. These components were integrated into a single probe, enabling both OCT and US imaging at the same time. In vitro OCT and ultrasound images of a rabbit aorta were obtained using this dual-modality imaging system. This study demonstrates the feasibility of an OCT-US system for intravascular imaging, which is expected to have a prominent impact on early detection and characterization of atherosclerosis.
TL;DR: In vivo breast imaging with instrumentation that combines FD and CW NIR data acquisition in a single spectral reconstruction produces more accurate hemoglobin, water, and lipid results relative to FD data alone.
Abstract: Purpose: A NIRtomography system that combines frequency domain (FD) and continuous wave (CW) measurements was used to image normal and malignant breast tissues. Methods: FD acquisitions were confined to wavelengths less than 850 nm because of detector limitations, whereas light from longer wavelengths (up to 948 nm) was measured in CW mode with CCD-coupled spectrometer detection. The two data sets were combined and processed in a single spectrally constrained reconstruction to map concentrations of hemoglobin, water, and lipid, as well as scattering parameters in the breast. Results: Chromophore concentrations were imaged in the breasts of nine asymptomatic volunteers to evaluate their intrasubject and intersubject variability. Normal subject data showed physiologically expected trends. Images from three cancer patients indicate that the added CW data is critical to recovering the expected increases in water and decreases in lipid content within malignancies.Contrasts of 1.5 to twofold in hemoglobin and water values were found in cancers. Conclusions: In vivo breast imaging with instrumentation that combines FD and CW NIR data acquisition in a single spectralreconstruction produces more accurate hemoglobin, water, and lipid results relative to FD data alone.
TL;DR: It is demonstrated both in silico and experimentally that reconstructions of absorption structures based on wide-field patterned-light strategies are feasible and outperform classical point excitation schemes for similar data set sizes and that time-domain information is retained even though large spatial areas are illuminated.
Abstract: This investigation explores the feasibility of performing diffuse optical tomography based on time-domain wide-field illumination and detection strategies. Wide-field patterned excitation and detection schemes are investigated in transmittance geometry with time-gated detection channels. A Monte Carlo forward model is employed to compute the time-resolved Jacobians for rigorous light propagation modeling. We demonstrate both in silico and experimentally that reconstructions of absorption structures based on wide-field patterned-light strategies are feasible and outperform classical point excitation schemes for similar data set sizes. Moreover, we demonstrate that time-domain information is retained even though large spatial areas are illuminated. The enhanced time-domain data set allows for quantitative three-dimensional imaging in thick tissue based on relatively small data sets associated with much shorter acquisition times.
TL;DR: The combined US-OCT system demonstrated high resolution in visualizing superficial arterial structures while retaining deep penetration of ultrasonic imaging, and improved lateral resolution of US is improved due to focused ultrasonic beam.
Abstract: We report an integrated ultrasound (US) and optical coherence tomography (OCT) probe and system for intravascular imaging. The dual-function probe is based on a 50 MHz focused ring US transducer, with a centric hole for mounting OCT probe. The coaxial US and light beams are steered by a 45° mirror to enable coregistered US∕OCT imaging simultaneously. Lateral resolution of US is improved due to focused ultrasonic beam. Mirror effects on US were investigated and invitro imaging of a rabbit aorta has been carried out. The combined US-OCT system demonstrated high resolution in visualizing superficial arterial structures while retaining deep penetration of ultrasonic imaging.
TL;DR: Progress towards practical application of FD-CP-OCT in the setting of delicate microsurgical procedures such as intraocular retinal surgery is reported and a technique to quantitatively evaluate the spatial distribution of oxygen saturation levels in tissue is proposed.
Abstract: A single-arm interferometer-based optical coherence tomography (OCT) system known as common-path OCT (CP-OCT) is rapidly progressing towards practical application. Due in part to the simplicity and robustness of its design, Fourier domain CP-OCT (FD-CP-OCT) offers advantages in many endoscopic sensing and imaging applications. FD-CP-OCT uses simple, interchangeable fiber optic probes that are easily integrated into small and delicate surgical tools. The system is capable of providing not only high-resolution imaging but also optical sensing. Here, we report progress towards practical application of FD-CP-OCT in the setting of delicate microsurgical procedures such as intraocular retinal surgery. To meet the challenges presented by the microsurgical requirements of these procedures, we have developed and initiated the validation of applicable fiber optic probes. By integrating these probes into our developing imaging system, we have obtained high-resolution OCT images and have also completed a demonstration of their potential sensing capabilities. Specifically, we utilize multiple superluminescent diodes to demonstrate sub-3-μm axial resolution in water; we propose a technique to quantitatively evaluate the spatial distribution of oxygen saturation levels in tissue; and we present evidence supportive of the technology's surface sensing and tool guidance potential by demonstrating topological and motion compensation capabilities.
TL;DR: This work implements the full resampling process on a commercial graphics processing unit (GPU), distributing the necessary calculations to many stream processors that operate in parallel, thereby achieving full GPU-based signal processing without the need for extra resampled hardware.
Abstract: Fourier domain optical coherence tomography (FD-OCT) requires either a linear-in-wavenumber spectrometer or a computationally heavy software algorithm to recalibrate the acquired optical signal from wavelength to wavenumber. The first method is sensitive to the position of the prism in the spectrometer, while the second method drastically slows down the system speed when it is implemented on a serially oriented central processing unit. We implement the full resampling process on a commercial graphics processing unit (GPU), distributing the necessary calculations to many stream processors that operate in parallel. A comparison between several recalibration methods is made in terms of performance and image quality. The GPU is also used to accelerate the fast Fourier transform (FFT) and to remove the background noise, thereby achieving full GPU-based signal processing without the need for extra resampling hardware. A display rate of 25 frames/sec is achieved for processed images (1024×1024 pixels) using a line-scan charge-coupled device (CCD) camera operating at 25.6 kHz.