This paper presents a hand-held single-mode fiber-based polarization-sensitive optical coherence tomography (PS-OCT) system with a single input polarization state. One drawback of this system is that the polarization becomes arbitrary, which can be solved by placing a polarization controller in the sample arm. A calibration target with an azimuthally varying optic axis integrated with the handheld probe will provide an absolute orientation axis measurement. This significantly reduces cost, time and availability of PS-OCT for clinical applications. With the home-built PS-OCT, we investigate the reorganization of collagen and blood vessel in a wound on the dorsal side of the human hand.
A framework presented in this study demonstrates the ability of pressure sensors to aid in acquiring reliable OCT/OCTA images. A handheld OCT probe combined with a disposable attachment with built-in force sensors was developed and its potential for skin imaging was demonstrated. With the real-time pressure monitoring, an operator can easily determine whether the pressure applied to the skin is below the threshold of affecting OCT imaging and uniform so as to obtain repeatable OCTA images.
A novel polarization state tracing algorithm has been proposed to visualize depth-resolved birefringent information by using the polarization sensitive optical coherence tomography (PSOCT) system. This algorithm is compatible to the widely adopted single input PSOCT system which uses only one circularly polarized incident light. We demonstrate the ability of this method to visualize depth-resolved myocardial architecture in both healthy and infarcted rodent hearts (ex vivo) and collagen structures responsible for skin tension lines at various anatomical locations on the face of a healthy human volunteer (in vivo).
Aging alterations in dermal blood vessels have been investigated using Optical Coherence Tomography Angiography (OCTA). However, classifying the vessel’s type was previously limited. In this study, we focused on diameter-dependent vascular alterations in facial skin with age, developing 3D analytical methods to the OCTA data with removing tail-artifact. As a result, it was found that the number of micro-vessels, defined at 20–39 microns, decreased with age, which was inversely true for thick vessels (160–179 micron diameter). Our results suggest that the aging degree of dermal vessels may be uniquely assessed by the diameter-dependent vascular alterations using the OCTA.
This paper report the development of non-invasive multi-functional imaging system for dental applications. This system is capable of detecting: 1) autofluorescence of the enamel, 2) red porphyrin of plaque, 3) the 3D-tomography of the hard/soft tissues and 4) functional angiography of said 3D-tomography data. The imaging technique incorporates molecular imaging (via light-induced autofluorescence, or LAF), 3D-high-resolution structure (via optical coherence tomography, or OCT) and angiography (via functional OCT, or OCTA) into one single imaging probe and platform. This development is crucial for our future research that would look into possible links between our OCTA findings and other clinical indicator such as red-porphyrin of plaque, autofluorescence of enamel.
Pulsatile signals from the cutaneous blood flow could be informative for evaluating the health condition of an individual. One of the popular optical measuring devices, photoplethysmogram (PPG) is often used to detect the pulse signal from skin. However, the origin of the PPG signal still remains controversial. Benefiting from the non-invasive, label-free, 3D imaging tool, optical coherence tomography (OCT) is able to capture the intrinsic tissue signals at different penetration depth in high spatial and temporal resolution. Periodic pulse signal was observed by taking advantage of the optical microangiography (OMAG) algorithm which is sensitive to the motion of blood flow. The pulsatile pattern from the capillary and arteriole was successfully differentiated and their morphology showed distinct property at different local blood pressure. The pulse signal from the arteriole is more consistent and has similar waveform as the PPG signals. The result indicated that the PPG signal could be deceive by the mixing signal from the capillary bed and arterioles since it measures the total blood volume change in the plexuses. This study may shed some new light on understanding the mechanical property of how blood travel through different types of vasculature networks and elucidate its potential application in disease assessments.
Shear Wave Optical Coherence Elastography (SW-OCE) uses the speed of propagating shear waves to provide a quantitative measurement of localized shear modulus, making it a valuable technique for the elasticity characterization of tissues such as skin and ocular tissue. One of the main challenges in shear wave elastography is to induce a reliable source of shear wave; most of nowadays techniques use external vibrators which have several drawbacks such as limited wave propagation range and/or difficulties in non-invasive scans requiring precisions, accuracy. Thus, we propose linear phase array ultrasound transducer as a remote wave source, combined with the high-speed, 47,000-frame-per-second Shear-wave visualization provided by phase-sensitive OCT. In this study, we observed for the first time shear waves induced by a 128 element linear array ultrasound imaging transducer, while the ultrasound and OCT images (within the OCE detection range) were triggered simultaneously. Acoustic radiation force impulses are induced by emitting 10 MHz tone-bursts of sub-millisecond durations (between 50 μm – 100 μm). Ultrasound beam steering is achieved by programming appropriate phase delay, covering a lateral range of 10 mm and full OCT axial (depth) range in the imaging sample. Tissue-mimicking phantoms with agarose concentration of 0.5% and 1% was used in the SW-OCE measurements as the only imaging samples. The results show extensive improvements over the range of SW-OCE elasticity map; such improvements can also be seen over shear wave velocities in softer and stiffer phantoms, as well as determining the boundary of multiple inclusions with different stiffness. This approach opens up the feasibility to combine medical ultrasound imaging and SW-OCE for high-resolution localized quantitative measurement of tissue biomechanical property.
Shear wave optical coherence elastography (SW-OCE) is a quantitative approach to assess tissue structures and elasticity with high resolution, based on OCT. Shear wave imaging (SWI) is the foundation of shear wave elasticity imaging (SWEI), which is a quantitative approach to assess tissue structures and pathological status. In order to enhance elastography resolution to micron scale, the shear waves needs to be highly localized, with short wavelength and high frequency (second order of kHz), which also places stricter requirement on the temporal resolution requirements of SWI device. In this paper, we introduced two approaches to remotely induce high frequency shear waves within tissue samples: ultrasound acoustic radiation force impulse (ARFI), and high energy nanosecond pulsed laser. The maximum frequency of pulsed laser induced shear waves in tissue-mimicking phantoms can go up to 25 kHz, which is not possible to be captured and tracked by other SWI modalities. We use a custom-built SWI-OCT system to visualize and capture the nanometer scale shear waves, achieving a spatial resolution up to 15 um and frame rate of up to 92 kHz. The dynamic wave propagation data was then used for the reconstruction of localized wave velocity and elasticity. This study demonstrates the non-contact shear wave generation with pulsed laser source, and ultra-fast, high-resolution sectional acoustical wave tracking with remarkable sensitivity, promising a future clinical application for a high-resolution quantitative mapping of elasticity in vivo, non-contact and real time in OCT-accessible tissue, especially in ocular tissues.
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