arXiv subjects

Jianlong Yang

Publications and source records attributed to Jianlong Yang.

24 records · Page 2Linked to original sources

arXiv2019

Deep learning enables extraction of capillary-level angiograms from single OCT volume

Optical coherence tomography angiography (OCTA) has drawn numerous attentions in ophthalmology. However, its data acquisition is time-consuming, because it is based on temporal-decorrelation principle thus requires multiple repeated volumetric OCT scans. In this paper, we developed a deep learning algorithm by combining a fovea attention mechanism with a residual neural network, which is able to extract capillary-level angiograms directly from a single OCT scan. The segmentation results of the inner limiting membrane and outer plexiform layers and the central $1\times1$ mm$^2$ field of view of the fovea are employed in the fovea attention mechanism. So the influences of large retinal vessels and choroidal vasculature on the extraction of capillaries can be minimized during the training of the network. The results demonstrate that the proposed algorithm has the capacity to better-visualizing capillaries around the foveal avascular zone than the existing work using a U-Net architecture.

physics.med-ph↗

arXiv2019

Eliminating Shadow Artifacts via Generative Inpainting Networks to Quantify Vascular Changes of the Choroid

Shadow artifacts from retinal vessels hinder the development of quantitative choroidal biomarkers in Optical Coherence Tomography (OCT), which limits the clinical applications of the choroidal OCT to the measures of layer thickness. In this paper, we present a novel framework that could eliminate the retinal shadows and realize the quantification of choroidal vasculature. Different from existing methods, we convert the shadow elimination into an object removal task, which can be handled by image inpainting techniques. We adopt and finetune a two-stage generative inpainting network which connects the edges of the vessels ahead of refilling the shadow-contaminated areas. It shows surpassing performance in repairing the choroidal vasculature compared with traditional inpainting algorithms. We further verify the feasibility of the proposed frame using a prospective observational study, which detects the choroidal vascular changes related to the Intra-Ocular Pressure (IOP) elevation of 34 healthy volunteers. As the average IOP increases from $15.84\pm1.99$ mmHg to $34.48\pm5.35$ mmHg, we achieve the decreases of the choroidal vessel density and flow index from $0.491\pm0.020$ to $0.463\pm0.019$ and from $0.336\pm0.025$ to $0.300\pm0.019$, respectively.

physics.med-ph↗

arXiv2018

Cascade-gain-switching for generating 3.5-um nanosecond pulses from monolithic low-cost fiber lasers

We propose a novel laser configuration that can output 3.5-$μ$m nanosecond laser pulses based on a simple and monolithic fiber structure. Cascade-gain-switching, which converts the wavelength of nanosecond pulses from 1.55 $μ$m to 3.5 $μ$m by two successive gain-switching processes. Instead of using expensive pump sources at special wavelengths and bulky active or passive modulation elements for Q-switching or mode-locking, the cascade gain-switching only requires the pumping of an electric-modulated 1.55-$μ$m pulsed laser and two continuous-wave (CW) 975-nm laser diodes. They are all standard products for fiber optic communication applications, which can greatly lower the cost of mid-infrared laser pulse generation. To investigate the feasibility of this configuration, we numerically simulated the cascade-gain-switching processes by comprehensive rate-equation models. In single-shot regime, for stable 3.5-$μ$m pulsed lasing, the CW 975-nm pump should be turned on at least $\sim500$ $μ$s ahead of the 1.55-$μ$m pulsed pump. It shows that the pulse width of the 1.55-$μ$m pump has major impact on the temporal shape of the intermediate 1.97-$μ$m pulse while has neglected influence on the generated 3.5-$μ$m pulse. On the other hand, increasing the CW pump power can significantly improve the output peak power and shorten the pulse when the pump power is less than $\sim4$ W. In the repetitive-pulse regime, we found the 3.5-$μ$m pulse train can be stably outputted when the repetition rate is $<=100$ kHz. As the repetition rate increases, the duration of reaching the stable operation increases. When the repetition rate is large than 100 kHz, the stable operation cannot be established because the rate of consuming the population on the $^4I_{11/2}$ level of $Er^{3+}$ ions is faster than the rate of building the population.

physics.optics↗

arXiv2017

Near-infrared laser thermal conjunctivoplasty

Conjunctivochalasis is a common cause of tear dysfunction due to the conjunctiva becoming loose and wrinkly with age. The current solutions to this disease include either surgical excision in the operating room, or thermoreduction of the loose tissue with hot wire in the clinic. We developed a near-infrared (NIR) laser thermal conjunctivoplasty (LTC) system, which gently shrinks the redundant tissue. The NIR light is mainly absorbed by water, so the heating is even and there is no bleeding. The system utilizes a 1460-nm programmable laser diode system as a light source. A miniaturized handheld probe delivers the laser light and focuses the laser into a 10x1 mm2 line. A foot pedal is used to deliver a preset number of calibrated laser pulses. A fold of loose conjunctiva is grasped by a pair of forceps. The infrared laser light is delivered through an optical fiber and a laser line is focused exactly on the conjunctival fold by a cylindrical lens. Ex vivo experiments using porcine eye were performed with the optimal laser parameters. It was found that up to 50% of conjunctiva shrinkage could be achieved.

physics.med-ph↗

arXiv2017

Polarization-multiplexed, dual-beam swept source optical coherence tomography angiography

A polarization-multiplexed, dual-beam setup is proposed to expand the field of view for a swept source optical coherence tomography angiography (OCTA) system. This method used a Wollaston prism to split sample path light into two orthogonal-polarized beams. This allowed two beams to shine on the cornea at an angle separation of ~ 14 degrees, which led to a separation of ~ 4.2 mm on the retina. A 3-mm glass plate was inserted into one of the beam paths to set a constant path length difference between the two polarized beams so the interferogram from the two beams are coded at different frequency bands. The resulting OCTA images from the two beams were coded with a depth separation of ~ 2 mm. 5x5 mm2 angiograms from the two beams were obtained simultaneously in 4 seconds. The two angiograms then were montaged to get a wider field of view (FOV) of ~ 5x9.2 mm2.

physics.med-ph↗

arXiv2015

Influences of pump transitions on thermal effects of multi-kilowatt thulium-doped fiber lasers

Thermal effects are critical constrains for developing high-power thulium-doped fiber lasers (TDFLs). In this paper, we numerically investigate the lasing and thermal characteristics of the TDFLs under different pump transitions. Our results show, the widely-used pump transition $^3H_6\rightarrow^3H_4$, taking advantages of high-power high-efficiency laser diodes at $\sim$0.8 $μ$m, may not be a superior choice for directly outputting multi-kilowatt at 2 $μ$m because of severe thermal problems. Meanwhile, using other pump transitions resulting 2-$μ$m emissions, especially the in-band pump transition $^3H_6\rightarrow^3F_4$, will decrease the generated heat to a large extent. By optimizing the power filling factor of the gain fiber, we find a 2-$μ$m TDFL cladding-pumped at 1.9 $μ$m will lead to the laser slope efficiency close to its quantum efficiency (95\%). The induced ultra-low quantum defect would be of great importance for power scaling. We thus propose tandem-pumped TDFLs for reducing the heat at high powers and discuss the related issues of design. Besides, we also explore the differences of the thermal characteristics between laser and superfluorescent operations, which will contribute to deepening the understanding of the thermal effects in high-power thulium-doped fiber amplifiers.

physics.optics↗