Improved adaptive complex diffusion despeckling filter

Despeckling optical coherence tomograms from the human retina is a fundamental step to a better diagnosis or as a preprocessing stage for retinal layer segmentation. Both of these applications are particularly important in monitoring the progression of retinal disorders. In this study we propose a new formulation for a well-known nonlinear complex diffusion filter. A regularization factor is now made to be dependent on data, and the process itself is now an adaptive one. Experimental results making use of synthetic data show the good performance of the proposed formulation by achieving better quantitative results and increasing computation speed.Fundação para a Ciência e TecnologiaFEDERPrograma COMPET

Optical Coherence Tomography guided Laser-Cochleostomy

Despite the high precision of laser, it remains challenging to control the laser-bone ablation without injuring the underlying critical structures. Providing an axial resolution on micrometre scale, OCT is a promising candidate for imaging microstructures beneath the bone surface and monitoring the ablation process. In this work, a bridge connecting these two technologies is established. A closed-loop control of laser-bone ablation under the monitoring with OCT has been successfully realised

Ultrasound-encoded optical tomography and time-reversed ultrasonically encoded optical focusing

Ultrasound modulated optical tomography is a developing hybrid imaging modality that combines high optical contrast and good ultrasonic resolution to image soft biological tissue. We developed a photorefractive crystal-based, time-resolved detection scheme with the use of a millisecond long ultrasound burst to image both the optical and mechanical properties of biological tissues, with improved detection efficiency of ultrasound-tagged photons. We also applied spectral-hole burning: SHB) aided detection in ultrasound-modulated optical tomography: UOT) to image optical heterogeneities in thick tissue-mimicking phantom samples and chicken breast tissue. The efficiency of SHB was improved by using a Tm3+: YAG crystal of higher doping concentration: 2.0-atomic%) and a double-pass pumping configuration. With the improved SHB-UOT system, we imaged absorbing, scattering, and phase contrast objects that were embedded in the middle plane of a 30-mm thick phantom sample. The imaging resolution was 0.5 mm in the lateral direction, as defined by the focal width of the ultrasonic transducer, and 1.5 mm in the axial direction, as determined by the ultrasonic burst length. We also imaged two absorbing objects embedded in the middle plane of a 32-mm thick chicken breast sample. The results suggest that the improved SHB-UOT system is one step closer to a practical optical imaging application in biological and clinical studies. Light focusing plays a central role in biomedical imaging, manipulation, and therapy. In optical scattering media such as biological tissue, light propagation is randomized by multiple scattering. Beyond one transport mean free path, where photon propagation is in the diffusive regime, direct light focusing becomes infeasible. Although various methods have been developed to overcome this optical diffusion limit, all are limited by the lack of a practical internal guide star. Here we proposed and experimentally validated a novel concept, called Time-Reversed Ultrasonically Encoded: TRUE) optical focusing, to deliver light dynamically into any predefined location inside a scattering medium. First, diffused coherent light is encoded by an ultrasonic wave focused to a predefined location; then, the encoded component of the diffused light is time-reversed and consequently converges back to the ultrasonic focus. The ultrasonic encoding noninvasively provides a virtual internal guide star for the time reversal. The TRUE optical focus--dynamically defined by the ultrasonic focus--is unaffected by multiple scattering of light, which is especially desirable in biological tissue where ultrasonic scattering is ~1000 times weaker than optical scattering. Various fields, such as biomedical, colloidal, atmospheric, and ocean optics, can benefit from TRUE optical focusing. Further, the concept can be generalized for non-optical waves

Measurements of Three Dimensional Temperature Field in Fluids using Laser Interferometry

Non-intrusive measurement of fluid temperature using laser interferometry is reported. As a case study, results obtained in Rayleigh-Benard convection experiment are presented. Image processing operations required for the evaluation interferograms and extraction of quantitative data from the optical Images are discussed. Limited-view tomographic algorithms applicable to interferometry are discussed and compared in terms of reconstructed three-dimensional temperature fields. This study concludes that laser interferometry coupled with tomography promises a versatile tool for three-dimensional temperature and flow field measurements in fluids

Hyperspectral interferometry for single-shot profilometry and depth-resolved displacement field measurement

A new approach to the absolute measurement of two-dimensional optical path differences is presented in this thesis. The method, which incorporates a white light interferometer and a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype of the Hyperspectral Interferometry (HSI) system has been designed, constructed and tested for two types of measurement: for surface profilometry and for depth-resolved displacement measurement, both of which have been implemented so as to achieve single shot data acquisition. The prototype has been shown to be capable of performing a single-shot 3-D shape measurement of an optically-flat step-height sample, with less than 5% difference from the result obtained by a standard optical (microscope) based method. The HSI prototype has been demonstrated to be able to perform single-shot measurement with an unambiguous 352 (m depth range and a rms measurement error of around 80 nm. The prototype has also been tested to perform measurements on optically rough surfaces. The rms error of these measurements was found to increase to around 4× that of the smooth surface. For the depth-resolved displacement field measurements, an experimental setup was designed and constructed in which a weakly-scattering sample underwent simple compression with a PZT actuator. Depth-resolved displacement fields were reconstructed from pairs of hyperspectral interferograms. However, the experimental results did not show the expected result of linear phase variation with depth. Analysis of several possible causes has been carried out with the most plausible reasons being excessive scattering particle density inside the sample and the possibility of insignificant deformation of the sample due to insufficient physical contact between the transducer and the sample

Optical designs and image processing algorithms for optical coherence tomography detection of glaucoma

textOptical Coherence Tomography (OCT) is an optical tomography technique which provides high resolution non-invasive three-dimensional (3D) structural images of the sample based on coherent properties of light. The dissertation focuses on the use of OCT systems for detecting glaucoma, which is the second leading cause of blindness worldwide. First, as a prerequisite of analyzing ophthalmologic OCT images, a retinal sublayer segmentation algorithm is presented and implemented with GPU assisted computation. Then, a polarization-sensitive optical coherence tomography (PS-OCT) system was constructed for the study of glaucoma. Three closely related clinical and animal studies on early-stage glaucoma detection using either OCT or PS-OCT were performed. Statistical analysis of the study results indicates that the scattering property of retinal nerve fiber layer (RNFL) is the earliest indicator for glaucoma. Finally, to investigate the scattering properties of RNFL, a pathlength-multiplexed scattering-angle-diverse optical coherence tomography (PM-SAD-OCT) system was designed and built. PM-SAD-OCT images were collected from human and rodent retina as well as earthworm nerve cord. PM-SAD-OCT system shows promising potentials to detect neurodegenerative diseases including glaucoma.Biomedical Engineerin

MULTIMODAL NONCONTACT DIFFUSE OPTICAL REFLECTANCE IMAGING OF BLOOD FLOW AND FLUORESCENCE CONTRASTS

In this study we design a succession of three increasingly adept diffuse optical devices towards the simultaneous 3D imaging of blood flow and fluorescence contrasts in relatively deep tissues. These metrics together can provide future insights into the relationship between blood flow distributions and fluorescent or fluorescently tagged agents. A noncontact diffuse correlation tomography (ncDCT) device was firstly developed to recover flow by mechanically scanning a lens-based apparatus across the sample. The novel flow reconstruction technique and measuring boundary curvature were advanced in tandem. The establishment of CCD camera detection with a high sampling density and flow recovery by speckle contrast followed with the next instrument, termed speckle contrast diffuse correlation tomography (scDCT). In scDCT, an optical switch sequenced coherent near-infrared light into contact-based source fibers around the sample surface. A fully noncontact reflectance mode device finalized improvements by combining noncontact scDCT (nc_scDCT) and diffuse fluorescence tomography (DFT) techniques. In the combined device, a galvo-mirror directed polarized light to the sample surface. Filters and a cross polarizer in stackable tubes promoted extracting flow indices, absorption coefficients, and fluorescence concentrations (indocyanine green, ICG). The scDCT instrumentation was validated through detection of a cubical solid tissue-like phantom heterogeneity beneath a liquid phantom (background) surface where recovery of its center and dimensions agreed with the known values. The combined nc_scDCT/DFT identified both a cubical solid phantom and a tube of stepwise varying ICG concentration (absorption and fluorescence contrast). The tube imaged by nc_scDCT/DFT exhibited expected trends in absorption and fluorescence. The tube shape, orientation, and localization were recovered in general agreement with actuality. The flow heterogeneity localization was successfully extracted and its average relative flow values in agreement with previous studies. Increasing ICG concentrations induced notable disturbances in the tube region (≥ 0.25 μM/1 μM for 785 nm/830 nm) suggesting the graduating absorption (320% increase at 785 nm) introduced errors. We observe that 830 nm is lower in the ICG absorption spectrum and the correspondingly measured flow encountered less influence than 785 nm. From these results we anticipate the best practice in future studies to be utilization of a laser source with wavelength in a low region of the ICG absorption spectrum (e.g., 830 nm) or to only monitor flow prior to ICG injection or post-clearance. In addition, ncDCT was initially tested in a mouse tumor model to examine tumor size and averaged flow changes over a four-day interval. The next steps in forwarding the combined device development include the straightforward automation of data acquisition and filter rotation and applying it to in vivo tumor studies. These animal/clinical models may seek information such as simultaneous detection of tumor flow, fluorescence, and absorption contrasts or analyzing the relationship between variably sized fluorescently tagged nanoparticles and their tumor deposition relationship to flow distributions