Realization of augmented reality (AR) solutions is key towards the much-needed integration of digital content into the real world. This seamless integration of digital content with the real world in AR devices is achieved by displaying the information using a suitable projector in the field-of-view (FOV) of the user. One of the most practical solutions to realize this is a laser beam scanner (LBS) projector combined with a diffractive optical waveguide. Features such as a small form factor, high brightness, large color gamut, and low power-consumption make LBS a popular choice as the light engine for the emerging consumer market for AR displays where the primary focus is on obtaining a stylish wearable rather than an unwieldly head mounted device. As should be the case for any AR/VR/MR display, LBS plus waveguide solution must be evaluated against the IEC 60825- 1:2014 standard for a typical use case. In this manuscript, we will first describe a typical AR solution, a TriLite Trixel® 3 LBS plus a waveguide combiner. We will discuss the operating principle of such a device. Based on that we shall highlight stepwise the key considerations in such a system for ensuring a Class 1 operation in a typical AR use case as per the IEC 60825-1:2014 requirements.
KEYWORDS: Optical coherence tomography, Wavelets, Digital filtering, Speckle, Signal to noise ratio, Denoising, Image filtering, Skin, Optical filters, Imaging systems
Significance: Speckle noise limits the diagnostic capabilities of optical coherence tomography (OCT) images, causing both a reduction in contrast and a less accurate assessment of the microstructural morphology of the tissue.
Aim: We present a speckle-noise reduction method for OCT volumes that exploits the advantages of adaptive-noise wavelet thresholding with a wavelet compounding method applied to several frames acquired from consecutive positions. The method takes advantage of the wavelet representation of the speckle statistics, calculated properly from a homogeneous sample or a region of the noisy volume.
Approach: The proposed method was first compared quantitatively with different state-of-the-art approaches by being applied to three different clinical dermatological OCT volumes with three different OCT settings. The method was also applied to a public retinal spectral-domain OCT dataset to demonstrate its applicability to different imaging modalities.
Results: The results based on four different metrics demonstrate that the proposed method achieved the best performance among the tested techniques in suppressing noise and preserving structural information.
Conclusions: The proposed OCT denoising technique has the potential to adapt to different image OCT settings and noise environments and to improve image quality prior to clinical diagnosis based on visual assessment.
Laser beam scanners (LBS) are an emerging micro-display technology for augmented reality (AR) head-mounted displays (HMD), enabling small-form-factor and low-power display units with large field of view (FOV) and daylight-bright luminance, that are compatible with a large range of optical combiner technologies such as waveguide or holographic combiners. We have developed an ultra-compact and lightweight LBS comprising an integrated laser module, a single 2D micro-electro-mechanical systems (MEMS) mirror, and a molded interconnect device (MID). The compact integrated laser module contains red, green, and blue (RGB) semiconductor laser diodes (LDs) and a common system of microlenses for beam collimation, all enclosed in a single hermetically sealed package. The three LDs are mounted onto a single submount using a novel high-precision laser die bonding technique. This high-precision LD placement allows the use of collimation lenses that collimate all three laser beams simultaneously in contrast to separate lenses with additional active alignment steps for each color. No additional optical components such as mirrors and dichroic beam combiners are required—instead, the color channels are overlapped on a pixel-by-pixel basis by a “software beam combination” laser pulse timing algorithm. Both laser module and MEMS mirror are assembled on an MID with printed circuit board (PCB), which is connected to a driver board including video interface. We also give an outlook to future generations of fully mass manufacturable LBS systems with even smaller form factor.
All optical photoacoustic tomography (PAT) using a planar Fabry-Perot interferometer polymer film sensor has been demonstrated for in vivo human palm imaging with an imaging penetration depth of 5 mm. The relatively larger vessels in the superficial plexus and the vessels in the dermal plexus are visible in PAT. However, due to both resolution and sensitivity limits, all optical PAT cannot reveal the smaller vessels such as capillary loops and venules. Melanin absorption also sometimes causes difficulties in PAT to resolve vessels. Optical coherence tomography (OCT) based angiography, on the other hand, has been proven suitable for microvasculature visualization in the first couple millimeters in human. In our work, we combine an all optical PAT system with an OCT system featuring a phase stable akinetic swept source. This multimodal PAT/OCT/OCT-angiography system provides us co-registered human skin vasculature information as well as the structural information of cutaneous. The scanning units of the sub-systems are assembled into one probe, which is then mounted onto a portable rack. The probe and rack design gives six degrees of freedom, allowing the multimodal optical imaging probe to access nearly all regions of human body. Utilizing this probe, we perform imaging on patients with various skin disorders as well as on healthy controls. Fused PAT/OCT-angiography volume shows the complete blood vessel network in human skin, which is further embedded in the morphology provided by OCT. A comparison between the results from the disordered regions and the normal regions demonstrates the clinical translational value of this multimodal optical imaging system in dermatology.
Studies have proven the relationship between cutaneous vasculature abnormalities and dermatological disorders, but to image vasculature noninvasively in vivo, advanced optical imaging techniques are required. In this study, we imaged a palm of a healthy volunteer and three subjects with cutaneous abnormalities with photoacoustic tomography (PAT) and optical coherence tomography with angiography extension (OCTA). Capillaries in the papillary dermis that are too small to be discerned with PAT are visualized with OCTA. From our results, we speculate that the PA signal from the palm is mostly from hemoglobin in capillaries rather than melanin, knowing that melanin concentration in volar skin is significantly smaller than that in other areas of the skin. We present for the first time OCTA images of capillaries along with the PAT images of the deeper vessels, demonstrating the complementary effective imaging depth range and the visualization capabilities of PAT and OCTA for imaging human skin in vivo. The proposed imaging system in this study could significantly improve treatment monitoring of dermatological diseases associated with cutaneous vasculature abnormalities.
The combination of photoacoustic tomography (PAT) with optical coherence tomography (OCT) has seen steady progress over the past few years. With the benchtop and semi-benchtop configurations, preclinical and clinical results have been demonstrated, paving the way for wider applications using dual modality PAT/OCT systems. However, as for the most updated semi-benchtop PAT/OCT system which employs a Fabry-Perot polymer film sensor, it is restricted to only human palm imaging due to the limited flexibility of the probe. The passband limit of the polymer film sensor further restricts the OCT source selection and reduces the sensitivity of the combined OCT system. To tackle these issues, we developed an articulated PAT/OCT probe for both preclinical and clinical applications. In the probe design, the sample arm of OCT sub-system and the interrogation part of the PAT sub-system are integrated into one compact unit. The polymer film sensor has a quick release function so that before each OCT scan, the sensor can be taken off to avoid the sensitivity drop and artefacts in OCT. The holding mechanism of the sensor is also more compact compared to previous designs, permitting access to uneven surfaces of the subjects. With the help of the articulated probe and a patient chair, we are able to perform co-registered imaging on human subjects on both upper and lower extremities while they are at rest positions. An increase in performance characteristics is also achieved. Patients with skin diseases are currently being recruited to test its clinical feasibility.
We present a novel akinetic optical ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-P´erot interferometer (FPI) with a central opening. The sensing principle relies exclusively on the detection of pressure-induced changes of the refractive index in the liquid located between the cavity mirrors. This enables resonance-free, inherently linear signal detection over a large bandwidth. We demonstrate that the sensor allows to realize exceedingly low noise equivalent pressure (NEP) values of 2 Pa over a 20 MHz measurement bandwidth, while maintaining a large full field of view of 2,7mm × 1,3mm as well as a flat frequency response. Imaging tests on phantoms and biological tissue show the suitability of the XARION-sensor for optical resolution photoacoustic microscopy (OR-PAM) applications. Transparent in axial direction, the sensor facilitates the implementation of highly sensitive fast-scanning reflection-mode OR-PAM setups, as well as easy integration with other imaging modalities such as confocal microscopy or OCT.
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