Polarized light interaction with media can reveal the microstructure and anisotropy of complex media beyond what can be obtained from scalar light interaction. Here, we present reciprocal polar decomposition for the backscattering Mueller matrices, a new Mueller matrix decomposition method for analyzing chiral and nonchiral complex media measured in reflection geometry. Reciprocal polar decomposition uniquely accounts for the reciprocity of the optical wave in forward and backward scattering paths. We demonstrate the superiority of the reciprocal polar decomposition against Lu-Chipman and differential Mueller matrix decompositions in various applications of backscattering polarimetry for birefringent targets, tissue sections, and chiral media. We also report examples where Lu-Chipman and differential decompositions produce incorrect media properties, whereas reciprocal polar decomposition succeeds. Reciprocal polar decomposition will open up diverse applications of backscattering polarimetry for biomedicine.
We report holistic quantification of cutaneous microcirculation with spatial frequency domain imaging (SFDI) and coherent hemodynamics spectroscopy (CHS) based on a dynamic microcirculation PIPE model. A simple device was developed to induce periodic variations in cutaneous blood volume and flow velocity. Both baseline and dynamic features of cutaneous microcirculation for healthy subjects were completely quantified. The CHS findings were further related to SSMD-SFDI imaging of the same healthy subjects under reactive hyperemia protocol. The results demonstrate spatial frequency domain imaging and coherent hemodynamics spectroscopy based on the dynamic microcirculation PIPE model provides a valuable tool for functional studies with hemodynamic-based techniques.
Most cancers originate from epithelium, the top layer of mucosa. We report single-snapshot Spatial Frequency Domain Imaging (SFDI) of mucosa with visible modulated light. A novel two-layer mucosa model enables the mapping of the total hemoglobin concentration, the oxygen saturation, the scattering characteristics of the top and bottom layers, and the thickness of the top layer from a single-snapshot. After validating with phantom studies, we demonstrate its applicability to the characterization of mucosa by imaging human mouth lips of healthy subjects. The proposed approach may find important applications in screening mucosa for early detection of cancer and other diseases.
We present Fermat single pixel camera for visible to SWIR biomedical imaging by encoding the spatial coordinate of the diffuse reflectance into different temporal modulation frequencies. The recovered reflectance spatial profile was then used to characterize the optical parameters of the specimen. The results from measurement on optical phantoms and biological tissues suggest Fermat single pixel camera can successfully quantify the optical properties over the visible to SWIR spectral range and may find valuable applications in imaging without a conventional camera.
We present a spatial frequency domain imaging (SFDI) study of local hemodynamics in the human finger cuticle of healthy volunteers performing paced breathing and the forearm of healthy young adults performing normal breathing with our recently developed Real Time Single Snapshot Multiple Frequency Demodulation – Spatial Frequency Domain Imaging (SSMD-SFDI) system. A two-layer model was used to map the concentrations of deoxy-, oxy-hemoglobin, melanin, epidermal thickness and scattering properties at the subsurface of the forearm and the finger cuticle. The oscillations of the concentrations of deoxy- and oxy-hemoglobin at the subsurface of the finger cuticle and forearm induced by paced breathing and normal breathing, respectively, were found to be close to out-of-phase, attributed to the dominance of the blood flow modulation by paced breathing or heartbeat. Our results suggest that the real time SFDI platform may serve as one effective imaging modality for microcirculation monitoring.
Wide-field tissue imaging is usually not capable of resolving tissue microstructure. We present High Spatial Frequency Domain Imaging (HSFDI) - a noncontact imaging modality that spatially maps the tissue microscopic scattering structures over a large field of view. Based on an analytical reflectance model of sub-diffusive light from forward-peaked highly scattering media, HSFDI quantifies the spatially-resolved parameters of the light scattering phase function from the reflectance of structured light modulated at high spatial frequencies. We have demonstrated with ex vivo cancerous tissue to validate the robustness of HSFDI in significant contrast and differentiation of the microstructutral parameters between different types and disease states of tissue.
We have presented a novel Single Snapshot Multiple Frequency Demodulation (SSMD) method enabling single snapshot wide field imaging of optical properties of turbid media in the Spatial Frequency Domain. SSMD makes use of the orthogonality of harmonic functions and extracts the modulation transfer function (MTF) at multiple modulation frequencies and of arbitrary orientations and amplitudes simultaneously from a single structured-illuminated image at once. SSMD not only increases significantly the data acquisition speed and reduces motion artifacts but also exhibits excellent noise suppression in imaging as well. The performance of SSMD-SFDI is demonstrated with experiments on both tissue mimicking phantoms and in vivo for recovering optical properties. SSMD is ideal in the implementation of a real-time spatial frequency domain imaging platform, which will open up SFDI for vast applications in, for example, mapping the optical properties of a dynamic turbid medium or monitoring fast temporal evolutions.
We present a spatial frequency domain imaging (SFDI) study of local hemodynamics in the forearm of healthy volunteers performing paced breathing. Real time Single Snapshot Multiple Frequency Demodulation - Spatial Frequency Domain Imaging (SSMD-SFDI) was used to map the optical properties of the subsurface of the forearm continuously. The oscillations of the concentrations of deoxy- and oxyhemoglobin at the subsurface of the forearm induced by paced breathing are found to be close to out-of-phase, attributed to the dominance of the blood flow modulation by paced breathing. The properties of local microcirculation including the blood transit times through capillaries and venules are extracted by fitting to Simplified Hemodynamics Model. Our preliminary results suggest that the real time SSMD-SFDI platform may serve as one effective imaging modality for microcirculation monitoring.
The Spatial-frequency dependence of turbid media reflectance encodes both optical properties and depth information. The high spatial frequency domain imaging (HSFDI) can, in particular, extract key characteristics of the phase function of the scattering medium which carries the ultimate structural information of the medium. We first outline the principle of HSFDI and then present here a compact optical configuration integrating the modulated illumination and imaging systems, facilitating quantitative wide-field optical properties mapping at high spatial frequencies. The performance of HSFDI is assessed on both tissue phantoms and in vivo.
Interferometry is one of the most efficient techniques in surface figure testing while the transmission surface usually limits the accuracy. Besides, standard figure interferometers often have a typical aperture of about 150 mm diameter which can not satisfy the need of large optics calibration. A novel method for characterizing the absolute surface figure of long grazing-incidence optics used in synchrotron radiation beamlines is presented. We demonstrate oblique incidence interferometry to overcome the aperture limitation. Furthermore, multiple rotating measurements are used to remove the transmission surface errors. The new solution is simple and easy without dismantling the transmission flat throughout the calibration procedure. The theoretical derivation, experiment results and uncertainty analysis are presented.
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