In this work, a synchronized dual-modal imaging system is used for in-vivo, non-contact ophthalmic imaging. The apparatus is comprised of both Photoacoustic Remote Sensing (PARS) and Swept-Source Optical Coherence Tomography (SS-OCT) subsystems. The PARS utilizes a multi-wavelength excitation source to target hemoglobin absorption and an 830 nm interrogation source to detect photoacoustic signals. PARS provides the measurements for computing blood oxygen saturation (sO2) mapping in the mouse and rat eyes. Meanwhile, a 1060 nm SS-OCT is employed to obtain volumetric tissue structure. To our knowledge, this is the first report of non-contact functional photoacoustic imaging in ophthalmic applications.
We present a new technique for improving the temporal stability of the Stimulated Raman Scattering (SRS)-based multispectral pulsed source by decreasing the temperature of the SRS medium. This technique reduces temporal fluctuations of the output SRS peaks, generates stable multiwavelength light, improves repeatability and accuracy of functional measurements. This stabilized temperature-regulated SRS-based source is combined with the wide field of view photoacoustic remote sensing microscope utilizing a telecentric scan lens as an imaging objective. In-vivo functional imaging experiments of the chorioallantois membrane of a chicken embryo (CAM) are performed for validation purposes.
A non-contact, dual-modal imaging apparatus is introduced which will be used to obtain the Metabolic Rate of Oxygen (mRO2) in the live murine eye, based on the blood flow rate and blood Oxygen Saturation (sO2) measurements. The apparatus is comprised of both Photoacoustic Remote Sensing (PARS) and Swept-Source Optical Coherence Tomography (SS-OCT) systems, operating synchronously. A phantom model will be imaged using the proposed system to validate the accuracy of the blood flow and sO2 measurements. To the best of our knowledge, this work would report for the first time, non-contact, in-vivo measurement of the mRO2 in the ophthalmic tissues.
A combined Photoacoustic Remote Sensing (PARS™) microscope and Optical Coherence Tomography (OCT) system is used to capture label-free wide-field high-resolution three-dimensional visualizations of nuclear morphology in unprocessed resected tissues.
A dual-modal optical imaging system combining photoacoustic remote sensing (PARS) and swept-source optical coherence tomography (SS-OCT) is presented. The PARS subsystem utilized a pulsed excitation beam at 532 nm confocal with a low-coherence interrogation beam centered at 830 nm to detect photoacoustic signals. The OCT subsystem employs a 1060 nm VCSEL swept source with a 60 kHz A-scan rate and 8 μm axial resolution in tissue. Volumetric images were acquired from carbon fibers and in-vivo biological tissues. To our knowledge, this is the first study demonstrating a combination of SS-OCT with optical-resolution photoacoustic microscopy for in-vivo, non-contact imaging of tissues.
We developed a deep learning system for inferring detailed retinal blood flow in structural optical coherence tomography (OCT) images. Motivations include enhanced diagnosis of retinal diseases and reducing time and cost of acquiring OCT angiography (OCTA) images. Using OCTA images as ground truth, we trained a conditional generative adversarial network (cGAN) to predict capillaries from OCT cross-sections. The inferred cross-sections and resulting en-face blood flow map images show comparable detail of small capillaries to the target images. The results demonstrate the potential of cGANs in inferring blood flow maps from new and existing retinal OCT datasets.
Currently, clinical in-vivo imaging of the human limbus cellular structure is only possible with in-vivo confocal microscopy (IVCM). However, IVCM requires physical contact with the imaged object, and may cause incidental tearing or inflammation of the limbal tissue. We present a line-field, spectral-domain OCT system (LF-SD-OCT) that can generate volumetric, cellular resolution images of biological tissue in-vivo and without contact. The system provides 1.7 µm axial and 2.2 × 3.1 µm lateral resolution in tissue and 2.5 kHz frame rate. The quality of healthy human limbus images acquired with LF-SD-OCT is comparable to that of IVCM.
A line-field, spectral-domain optical coherence tomography (LF-SD-OCT) system was build for in-vivo, non-contact, cellular resolution imaging of biological tissue at 2.5 kHz frame rate. Test images acquired from healthy human subjects show that the LF-SD-OCT is able to image the cellular structure of semitransparent tissue such as the human cornea, as well as highly scattering tissue such as skin. This system may serve as a valuable diagnostic tool to ophthalmologists and dermatologists for diagnosis and monitoring the treatment of various corneal and skin diseases.
The corneal sub-basal nerve plexus (SNP) is a network of thin, unmyelinated nerve fibers located between the basal epithelium and the Bowman’s membrane. Both corneal and systemic diseases such as keratoconus and diabetic can alter the nerve fiber density, thickness and tortuosity. Recent developments of cellular resolution OCT technology allowed for in-vivo visualization and mapping of the corneal SNP. We have developed a fully automated algorithm for segmentation of corneal nerves. The performance of the algorithm was tested on a series of enface UHR-OCT images acquired in-vivo from healthy human subjects. The proposed algorithm traces most of the sub-basal corneal nerves correctly. The achieved processing time and tracing quality are the major advantages of the proposed method. Results show the potential application of proposed method for nerve analysis and morphometric quantification of human sub-basal corneal nerves which is an important tool in corneal related diseases.
A line-field, spectral domain optical coherence tomography (LF-SD-OCT) system was developed for in-vivo, noncontact, cellular resolution imaging of biological tissue. The LF-SD-OCT system utilizes a broadband laser with a spectrum centered at ~790 nm and spectral bandwidth of ~140 nm to achieve 1.8 μm axial and ~5 μm isotropic lateral resolution in biological tissue. A high speed 2D camera was used to achieve frame rate of 2.5k B-scans/s. The system’s SNR was measured to be 92 dB at 100 μm away from the zero-delay line for 2.8 mW optical power incident on the imaged object, with 18 dB roll-off over a scanning range of 1 mm. The LF-SD-OCT system was used to image the cellular structure of cucumber and the cucumber seed where the high spatial resolution was sufficient to resolve cellular nuclei. Then the system was used to image in-vivo human skin (fingertip), where the spiral structures of the sweat glands, as well as a large number of capillaries were observed in the epidermal layer. Images of the healthy human cornea were also acquired from locations near the corneal apex and the periphery and showed the tissue cellular structure and vasculature. Currently, the corneal images were acquired ex-vivo, as we are waiting for ethics clearance to conduct in-vivo corneal imaging studies with the novel LF-SD-OCT system.
Limbal stem cell dysfunction (LSCD) causes morphological and physiological changes in the limbus that result in decreased vision, photophobia, tearing, chronic inflammation and hyperemia, recurrent episodes of pain, and blindness in severe cases. Currently, clinical in-vivo imaging of the palisaded of Vogt (POV) and the cellular structure of the limbal crypts in the human corneo-scleral limbus is accomplished by in-vivo confocal microscopy (IVCM). However, IVCM requires physical contact with the limbal tissue that can cause pain and inflammation. In this study, we used a novel high speed, ultra-high resolution optical coherence tomography (UHR-OCT) system to generate volumetric, cellular resolution image of the healthy and pathological human corneo-scleral limbus. The UHR-OCT system has a compact fiber-optic design. A femtosecond laser with 790 nm central wavelength and ~150 nm spectral bandwidth (at 3dB) was used to achieve ~1.4 µm axial resolution in biological tissue. The UHR-OCT system also utilizes a high resolution spectrometer (Cobra, Wasatch Photonics) connected to a novel line scan camera with a tall pixel design, 2048 pixel array and a maximum readout rate of 250 kHz. The system’s SNR was 96 dB at 100 µm away from the zero delay line, with ~10 dB roll-off over 1.5 mm scanning range for ~800 µm power of the imaging beam. Volumetric images of the POV and the cellular structure of the limbal crypts were acquired in-vivo and without contact with the limbal tissue from healthy and LSCD and subjects. This study was approved by the University of Waterloo Research Ethics Committee.
Degenerative conditions such as keratoconus and Fuch’s dystrophy can alter over time the cellular structure of the human corneal epithelium and endothelium respectively. A high-speed UHR-OCT system, capable of generating volumetric images of the cellular structure of the human cornea was built. The UHR-OCT system has a compact fiber-optic design that utilizes a commercial femtolaser with the central wavelength of 790 nm and 3dB spectral bandwidth of 150 nm to achieve ~ 1.4 µm axial resolution in corneal tissue. The optical design of the OCT imaging probe ensured ~2 µm OCT lateral resolution in corneal tissue. At the detection end of the UHR-OCT system, a high-resolution spectrometer (Cobra, Wasatch Photonics) is interfaced with a novel line scan camera. The camera has a tall pixel design, 2048 pixel array and a maximum readout rate of 250 kHz. The system’s SNR was 96 dB at 100 µm away from the zero delay line, with a 10 dB roll-off over 1.5 mm scanning range for ~800 µm power of the imaging beam incident on the corneal surface. Volumetric images of healthy and pathological corneas were acquired in-vivo from healthy volunteers and subjects with keratoconus and Fuch’s dystrophy and the images were compared with typical histological images. This study was approved by the University of Waterloo Research Ethics Committee.
The variability in the spatial orientation of retinal blood vessels near the optic nerve head (ONH) results in imprecision of the measured Doppler angle and therefore the pulsatile blood flow (BF), when those parameters are evaluated using Doppler OCT imaging protocols based on dual-concentric circular scans. Here, we utilized a dense concentric circle scanning protocol and evaluated its precision for measuring pulsatile retinal BF in rats for different numbers of the circular scans. An spectral domain optical coherence tomography (SD-OCT) system operating in the 1060-nm spectral range with image acquisition rate of 47,000 A-scans/s was used to acquire concentric circular scans centered at the rat’s ONH, with diameters ranging from 0.8 to 1.0 mm. A custom, automatic blood vessel segmentation algorithm was used to track the spatial orientation of the retinal blood vessels in three dimensions, evaluate the spatially dependent Doppler angle and calculate more accurately the axial BF for each major retinal blood vessel. Metrics such as retinal BF, pulsatility index, and resistance index were evaluated for each and all of the major retinal blood vessels. The performance of the proposed dense concentric circle scanning protocols was compared with that of the dual-circle scanning protocol. Results showed a 3.8±2.2 deg difference in the Doppler angle calculation between the two approaches, which resulted in ∼7% difference in the calculated retinal BF.
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