Mircea Mujat

Adaptive optics scanning laser ophthalmoscope with integrated wide-field retinal imaging and tracking

We have developed a new, unified implementation of the adaptive optics scanning laser ophthalmoscope (AOSLO) incorporating a wide-field line-scanning ophthalmoscope (LSO) and a closed-loop optical retinal tracker. AOSLO raster scans are deflected by the integrated tracking mirrors so that direct AOSLO stabilization is automatic during tracking. The wide-field imager and large-spherical-mirror optical interface design, as well as a large-stroke deformable mirror (DM), enable the AOSLO image field to be corrected at any retinal coordinates of interest in a field of >25 deg. AO performance was assessed by imaging individuals with a range of refractive errors. In most subjects, image contrast was measurable at spatial frequencies close to the diffraction limit. Closed-loop optical (hardware) tracking performance was assessed by comparing sequential image series with and without stabilization. Though usually better than 10 μm rms, or 0.03 deg, tracking does not yet stabilize to single cone precision but significantly improves average image quality and increases the number of frames that can be successfully aligned by software-based post-processing methods. The new optical interface allows the high-resolution imaging field to be placed anywhere within the wide field without requiring the subject to re-fixate, enabling easier retinal navigation and faster, more efficient AOSLO montage capture and stitching.

Dual-beam Fourier domain optical Doppler tomography of zebrafish

We have developed a dual-beam Fourier domain optical Doppler tomography (FD-ODT) system to image zebrafish (Danio rerio) larvae. Two beams incident on the zebrafish with a fixed angular separation allow absolute blood flow velocity measurement to be made regardless of vessel orientation in a sagittal plane along which the heart and most of the major vasculature lie. Two spectrometers simultaneously acquire spectra from two interferometers with a typical (maximum) line rate of 18 (28) kHz. The system was calibrated using diluted milk and microspheres and a 0.5-mm thick flow cell. The average deviation from the set velocity from 1.4 to 34.6 mm/s was 4.1%. Three-dimensional structural raster videos were acquired of an entire fish, and through the head, heart, and upper tail of the fish. Coarse features that were resolved include the telencephalon, retina, both heart chambers (atrium and ventricle), branchial arches, and notochord. Other fine structures within these organs were also resolved. Zebrafish are an important tool for high-throughput screening of new pharmacological agents. The ability to generate high-resolution three-dimensional structural videos and accurately measure absolute flow rates in major vessels with FD-ODT provides researchers with additional metrics by which the efficacy of new drugs can be assessed.

High resolution multimodal clinical ophthalmic imaging system

We developed a multimodal adaptive optics (AO) retinal imager which is the first to combine high performance AO-corrected scanning laser ophthalmoscopy (SLO) and swept source Fourier domain optical coherence tomography (SSOCT) imaging modes in a single compact clinical prototype platform. Such systems are becoming ever more essential to vision research and are expected to prove their clinical value for diagnosis of retinal diseases, including glaucoma, diabetic retinopathy (DR), age-related macular degeneration (AMD), and retinitis pigmentosa. The SSOCT channel operates at a wavelength of 1 µm for increased penetration and visualization of the choriocapillaris and choroid, sites of major disease activity for DR and wet AMD. This AO system is designed for use in clinical populations; a dual deformable mirror (DM) configuration allows simultaneous low- and high-order aberration correction over a large range of refractions and ocular media quality. The system also includes a wide field (33 deg.) line scanning ophthalmoscope (LSO) for initial screening, target identification, and global orientation, an integrated retinal tracker (RT) to stabilize the SLO, OCT, and LSO imaging fields in the presence of lateral eye motion, and a high-resolution LCD-based fixation target for presentation of visual cues. The system was tested in human subjects without retinal disease for performance optimization and validation. We were able to resolve and quantify cone photoreceptors across the macula to within ~0.5 deg (~100-150 µm) of the fovea, image and delineate ten retinal layers, and penetrate to resolve features deep into the choroid. The prototype presented here is the first of a new class of powerful flexible imaging platforms that will provide clinicians and researchers with high-resolution, high performance adaptive optics imaging to help guide therapies, develop new drugs, and improve patient outcomes.

A law of interference of electromagnetic beams of any state of coherence and polarization and the Fresnel–Arago interference laws

A new general interference law is derived for the superposition of two random electromagnetic beams of any state of coherence and of any state of polarization when the beams are transmitted through polarizers and rotators. It includes, as special cases, a variety of interference laws that apply to particular situations. Some of them have a close bearing on the classic interference experiments of Fresnel and Arago that have played a basic role in elucidating the concept of polarization of light.

Compact adaptive optics line scanning ophthalmoscope

We have developed a compact retinal imager that integrates adaptive optics (AO) into a line scanning ophthalmoscope (LSO). The bench-top AO-LSO instrument significantly reduces the size, complexity, and cost of research AO scanning laser ophthalmoscopes (AOSLOs), for the purpose of moving adaptive optics imaging more rapidly into routine clinical use. The AO-LSO produces high resolution retinal images with only one moving part and a significantly reduced instrument footprint and number of optical components. The AO-LSO has a moderate field of view (5.5 deg), which allows montages of the macula or other targets to be obtained more quickly and efficiently. In a preliminary human subjects investigation, photoreceptors could be resolved and counted within approximately 0.5 mm of the fovea. Photoreceptor counts matched closely to previously reported histology. The capillaries surrounding the foveal avascular zone could be resolved, as well as cells flowing within them. Individual nerve fiber bundles could be resolved, especially near the optic nerve head, as well as other structures such as the lamina cribrosa. In addition to instrument design, fabrication, and testing, software algorithms were developed for automated image registration and cone counting.

Polarimetric and spectral changes in random electromagnetic fields

Beginning with a recently formulated unified theory of coherence and polarization for random electromagnetic fields, we show how partially polarized light can be generated through correlation of unpolarized components. The effect is demonstrated by use of a Mach-Zehnder interferometer, showing the possibility of producing light with adjustable spectral density and an adjustable degree of polarization.

Interferometric imaging polarimeter

We describe a new imaging polarimeter that is based on a modified Sagnac interferometer and allows full polarimetric description of complex random electromagnetic beams from only two images as compared with the four images needed in conventional polarimetry. The procedure is analyzed in terms of the interference laws of Fresnel and Arago, and very good agreement with standard Stokes polarimetry is demonstrated. In certain cases the new technique provides the degree of polarization and the retardance from only one image.

Automated algorithm for breast tissue differentiation in optical coherence tomography

An automated algorithm for differentiating breast tissue types based on optical coherence tomography (OCT) data is presented. Eight parameters are derived from the OCT reflectivity profiles and their means and covariance matrices are calculated for each tissue type from a training set (48 samples) selected based on histological examination. A quadratic discrimination score is then used to assess the samples from a validation set. The algorithm results for a set of 89 breast tissue samples were correlated with the histological findings, yielding specificity and sensitivity of 0.88. If further perfected to work in real time and yield even higher sensitivity and specificity, this algorithm would be a valuable tool for biopsy guidance and could significantly increase procedure reliability by reducing both the number of nondiagnostic aspirates and the number of false negatives.

Fluorescence-guided optical coherence tomography imaging for colon cancer screening: a preliminary mouse study

A new concept for cancer screening has been preliminarily investigated. A cancer targeting agent loaded with a near-infrared (NIR) dye was topically applied on the tissue to highlight cancer-suspect locations and guide optical coherence tomography (OCT) imaging, which was used to further investigate tissue morphology at the micron scale. A pilot study on ApcMin mice has been performed to preliminarily test this new cancer screening approach. As a cancer-targeting agent, poly(epsilon-caprolactone) microparticles (PCLMPs), labeled with a NIR dye and functionalized with an RGD (argenine-glycine-aspartic acid) peptide, were used. This agent recognizes the ανβ3 integrin receptor (ABIR), which is over-expressed by epithelial cancer cells. The contrast agent was administered topically in vivo in mouse colon. After incubation, the animals were sacrificed and fluorescence-guided high resolution optical coherence tomography (OCT) imaging was used to visualize colon morphology. The preliminary results show preferential staining of the abnormal tissue, as indicated by both microscopy and laser-induced fluorescence imaging, and OCT’s capability to differentiate between normal mucosal areas, early dysplasia, and adenocarcinoma. Although very preliminary, the results of this study suggest that fluorescence-guided OCT imaging might be a suitable approach for cancer screening. If successful, this approach could be used by clinicians to more reliably diagnose early stage cancers in vivo.

Combined reflectance confocal microscopy/optical coherence tomography imaging for skin burn assessment

A combined high-resolution reflectance confocal microscopy (RCM)/optical coherence tomography (OCT) instrument for assessing skin burn gravity has been built and tested. This instruments allows for visualizing skin intracellular details with submicron resolution in the RCM mode and morphological and birefringence modifications to depths on the order of 1.2 mm in the OCT mode. Preliminary testing of the dual modality imaging approach has been performed on the skin of volunteers with some burn scars and on normal and thermally-injured Epiderm FTTM skin constructs. The initial results show that these two optical technologies have complementary capabilities that can offer the clinician a set of clinically comprehensive parameters: OCT helps to visualize deeper burn injuries and possibly quantify collagen destruction by measuring skin birefringence, while RCM provides submicron details of the integrity of the epidermal layer and identifies the presence of the superficial blood flow in the upper dermis. Therefore, the combination of these two technologies within the same instrument may provide a more comprehensive set of parameters that may help clinicians to more objectively and nonivasively assess burn injury gravity by determining tissue structural integrity and viability.