Detection of non-scattering domains (voids) is an area of active research in biomedical optics. To avoid complexities of image reconstruction algorithms and requirements of a priori knowledge of void ...locations inherent to diffuse optical tomography (DOT), it would be useful to establish specific experimental signatures of voids that would help identify and detect them by other means. To address this, we present a radiance-based spectro-angular mapping approach that identifies void locations in the angular domain and establishes their spectral features. Using water-filled capillaries in scattering Intralipid as a test platform, we demonstrate perturbations in the directional photon density distribution produced by individual voids.
Polarimetry is a noninvasive method that uses polarised light to assess biophysical characteristics of tissues. A series of incident polarisation states illuminates a biological sample, and analysis ...of sample-altered polarisation states enables polarimetric tissue assessment. The resultant information can, for example, help quantitatively differentiate healthy from pathologic tissue. However, most bio-polarimetric assessments are performed using free-space optics with bulky optical components. Extension to flexible fibre-based systems is clinically desirable, but is challenging due to polarisation-altering properties of optical fibres. Here, we propose a flexible fibre-based polarimetric solution, and describe its design, fabrication, calibration, and initial feasibility demonstration in ex vivo tissue. The design is based on a flexible fibre bundle of six multimode optical fibres, each terminated with a distal polariser that ensures pre-determined output polarisation states. The resultant probe enables linear 3 × 3 Mueller matrix characterization of distal tissue. Potential in vivo Mueller matrix polarimetric tissue examinations in various directly-inaccessible body cavities are envisioned.
Expanding the current endoscopic optical coherence tomography (OCT) system with Doppler capability may augment this novel high-resolution cross-sectional imaging technique with functional blood flow ...information. The aim of this feasibility study was to assess the clinical feasibility of an endoscopic Doppler OCT (EDOCT) system in the human GI tract.
During routine endoscopy, 22 patients were imaged by using a prototype EDOCT system, which provided color-Doppler and velocity-variance images of mucosal and submucosal blood flow at one frame per second, simultaneously with high-spatial-resolution (10-25 μm) images of tissue microstructure. The images were acquired from normal GI tract and pathologic tissues.
Subsurface microstructure and microcirculation images of normal and pathologic GI tissues, including Barrett's esophagus, esophageal varices, portal hypertensive gastropathy, gastric antral vascular ectasia, gastric lymphoma, and duodenal adenocarcinoma, were obtained from 72 individual sites in vivo. Differences in vessel diameter, distribution, density, and blood-flow velocity were observed among the GI tissue pathologies imaged.
To our knowledge, this is the first study to demonstrate the feasibility of EDOCT imaging in the human GI tract during routine endoscopy procedures. EDOCT may detect the different microcirculation patterns exhibited by normal and diseased tissues, which may be useful for diagnostic imaging and treatment monitoring.
Melanoma is the most aggressive type of skin cancer, with significant risk of fatality. Due to its pigmentation, light-based imaging and treatment techniques are limited to near the tumor surface, ...which is inadequate, for example, to evaluate the microvascular density that is associated with prognosis. White-light diffuse reflectance spectroscopy (DRS) and near-infrared optical coherence tomography (OCT) were used to evaluate the effect of a topically applied optical clearing agent (OCA) in melanoma in vivo and to image the microvascular network. DRS was performed using a contact fiber optic probe in the range from 450 to 650 nm. OCT imaging was performed using a swept-source system at 1310 nm. The OCT image data were processed using speckle variance and depth-encoded algorithms. Diffuse reflectance signals decreased with clearing, dropping by ∼90% after 45 min. OCT was able to image the microvasculature in the pigmented melanoma tissue with good spatial resolution up to a depth of ∼300 μm without the use of OCA; improved contrast resolution was achieved with optical clearing to a depth of ∼750 μm in tumor. These findings are relevant to potential clinical applications in melanoma, such as assessing prognosis and treatment responses. Optical clearing may also facilitate the use of light-based treatments such as photodynamic therapy.
In vivo and direct imaging of the murine spinal cord and its vasculature using multimodal (optical and acoustic) imaging techniques could significantly advance preclinical studies of the spinal cord. ...Such intrinsically high resolution and complementary imaging technologies could provide a powerful means of quantitatively monitoring changes in anatomy, structure, physiology and function of the living cord over time after traumatic injury, onset of disease, or therapeutic intervention. However, longitudinal in vivo imaging of the intact spinal cord in rodent models has been challenging, requiring repeated surgeries to expose the cord for imaging or sacrifice of animals at various time points for ex vivo tissue analysis. To address these limitations, we have developed an implantable spinal cord window chamber (SCWC) device and procedures in mice for repeated multimodal intravital microscopic imaging of the cord and its vasculature in situ. We present methodology for using our SCWC to achieve spatially co-registered optical-acoustic imaging performed serially for up to four weeks, without damaging the cord or induction of locomotor deficits in implanted animals. To demonstrate the feasibility, we used the SCWC model to study the response of the normal spinal cord vasculature to ionizing radiation over time using white light and fluorescence microscopy combined with optical coherence tomography (OCT) in vivo. In vivo power Doppler ultrasound and photoacoustics were used to directly visualize the cord and vascular structures and to measure hemoglobin oxygen saturation through the complete spinal cord, respectively. The model was also used for intravital imaging of spinal micrometastases resulting from primary brain tumor using fluorescence and bioluminescence imaging. Our SCWC model overcomes previous in vivo imaging challenges, and our data provide evidence of the broader utility of hybridized optical-acoustic imaging methods for obtaining multiparametric and rich imaging data sets, including over extended periods, for preclinical in vivo spinal cord research.
Characterization of tissues like brain by using magnetic resonance (MR) images and colorization of the gray scale image has been reported in the literature, along with the advantages and drawbacks. ...Here, we present two independent methods; (i) a novel colorization method to underscore the variability in brain MR images, indicative of the underlying physical density of bio tissue, (ii) a segmentation method (both hard and soft segmentation) to characterize gray brain MR images. The segmented images are then transformed into color using the above-mentioned colorization method, yielding promising results for manual tracing. Our color transformation incorporates the voxel classification by matching the luminance of voxels of the source MR image and provided color image by measuring the distance between them. The segmentation method is based on single-phase clustering for 2D and 3D image segmentation with a new auto centroid selection method, which divides the image into three distinct regions (gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) using prior anatomical knowledge). Results have been successfully validated on human T2-weighted (T2) brain MR images. The proposed method can be potentially applied to gray-scale images from other imaging modalities, in bringing out additional diagnostic tissue information contained in the colorized image processing approach as described.
We report a rapid time-gated full Stokes imaging approach without mechanically moving parts, which is well-suited for biomedical applications, using two photoelastic modulators (PEMs). A ...charge-coupled device (CCD) with microsecond time-gating capability was used to acquire the images. To synchronize the CCD with the PEMs, thus gaining signal-to-noise ratio advantage, a field programmable gate array was employed. After calibration, an evolutionary algorithm was used to select four time points from which the full Stokes vector can be recovered. Using the images taken by the camera at these four times (in ~80 ms), the images of the full Stokes vectors of different incident polarization states were accurately derived.
A novel optoacoustic phantom made of polyvinyl chloride-plastisol (PVCP) for optoacoustic studies is described. The optical and acoustic properties of PVCP were measured. Titanium dioxide (TiO2) ...powder and black plastic colour (BPC) were used to introduce scattering and absorption, respectively, in the phantoms. The optical absorption coefficient (mua) at 1064 nm was determined using an optoacoustic method, while diffuse reflectance measurements were used to obtain the optical reduced scattering coefficient (mu's). These optical properties were calculated to be mua = (12.818 +/- 0.001)ABPC cm(-1) and mu's = (2.6 +/- 0.2)S(TiO2) + (1.4 +/- 0.1) cm(-1), where ABPC is the BPC per cent volume concentration, and S(TiO2) is the TiO2 volume concentration (mg mL(-1)). The speed of sound in PVCP was measured to be (1.40 +/- 0.02) x 10(3) m s(-1) using the pulse echo transmit receive method, with an acoustic attenuation of (0.56 +/- 1.01) f(1.51+/-0.06)MHz (dB cm(-1)) in the frequency range of 0.61-1.25 MHz, and a density, calculated by measuring the displacement of water, of 1.00 +/- 0.04 g cm(-3). The speed of sound and density of PVCP are similar to tissue, and together with the user-adjustable optical properties, make this material well suited for developing tissue-equivalent phantoms for biomedical optoacoustics.
Development of methodologies for quantification/unique interpretation of the intrinsic polarimetry characteristics of biological tissues are important for various applications involving tissue ...characterization/diagnosis. A detailed comparative evaluation of the polar decomposition and the differential matrix decomposition of Mueller matrices for extraction/quantification of the intrinsic polarimetry characteristics (with special emphasis on linear retardance δ, optical rotation Ψ and depolarization Δ parameters was performed, because these are the most prominent tissue polarimetry effects) from complex tissue-like turbid media exhibiting simultaneous scattering and polarization effects. The results suggest that for media exhibiting simultaneous linear retardance and optical rotation polarization events, the use of retarder polar decomposition with its associated analysis which assumes sequential occurrence of these effects, results in systematic underestimation of δ and overestimation of Ψ parameters. Analytical relationships between the polarization parameters (δ, Ψ) extracted from both the retarder polar decomposition and the differential matrix decomposition for either simultaneous or sequential occurrence of the linear retardance and optical rotation effects were derived. The self-consistency of both decompositions is validated on experimental Mueller matrices recorded from tissue-simulating phantoms (whose polarization properties are controlled, known a-priori, and exhibited simultaneously) of increasing biological complexity. Additional theoretical validation tests were performed on Monte Carlo-generated Mueller matrices from analogous turbid media exhibiting simultaneous depolarization (Δ), linear retardance (δ) and optical rotation (Ψ) effects. After successful evaluation, the potential advantage of the differential matrix decomposition over the polar decomposition formalism was explored for monitoring of myocardial tissue regeneration following stem cell therapy.
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