Information retrieval from optical speckles is desired yet challenging. Insufficient sampling, especially in sub-Nyquist domain, of speckles significantly destroys the encoded information and correlations among these speckle grains. To address that, we trained a deep neural network to combat the physical imperfection: the sub-Nyquist sampled speckles (~14 below the Nyquist criterion) are interpolated up to a well-resolved level (322 times more pixels to resolve the same FOV) with smoothed morphology fine-textured, and more importantly, lost information retraced. With the FOV-resolution dilemma favorably overcome, it deepens our understanding of the scattering, enabling big and clear imaging in complex scenarios.
A panoramic imaging system has been developed using two afocal lenses and a smart phone that consists of cameras on both sides. An individual afocal lens has been developed with a large field of view (FOV) and a large exit pupil, which can enlarge the FOV of a smart phone camera to above 180 deg. Some issues with the smart phone-based 360-deg panoramic system, such as relative illuminance and assembly tolerance, were analyzed in detail and taken into consideration during the design procedure. A prototype has been developed with a low fabrication cost, yet producing impressive panoramic image quality.
In this paper, a novel method with high-speed angular steering device is presented to realize high angular resolution for the multi-projection based multi-view and light field 3D displays. The state-of-art multi-projection based multi-view and light field 3D displays always employ projector array with multi-layer structure to achieve high angular resolution, but the projector’s physical size still limits the angular resolution of 3D displays. To enhance the angular resolution of multiview and light field displays, a special designed angular steering optical device is integrated into the screen part of the display system, which is capable to deflect rays in a limited angular range to increase the density of projectors equivalently. A high-speed angular steering device is developed to deflect rays in a small angle based on the birefrigent effect of liquid crystal (LC), which mainly includes cascade structure of the pi cell LC and the birefringent LC microprism array. Furthermore, the steering angle control of this device can be well synchronized with the frame rate of projector array. With time-multiplexing of the steering angle, high angular resolution of multi-view and light field 3D displays with single-layer projector array are implemented. In our experiments, the developed angular steering device with steering angles of 0° and ±1° was successfully integrated into twelve-projector based multi-view and light field display systems to enhance the angular resolution respectively. The experimental results show that the angular resolution of the two different types of 3D displays is significantly enhanced to provide better visual experience for users.
Yunqi Luo, Huanhao Li, Ruochong Zhang, Puxiang Lai, and Yuanjin Zheng "Deep learning assisted optical wavefront shaping in disordered medium", Proc. SPIE 10886, Adaptive Optics and Wavefront Control for Biological Systems V, 1088612 (20 February 2019); doi: 10.1117/12.2504425
was published on 17 April 2019.
Details of the revision are provided in the text that accompanies this Erratum. The original paper has been updated.
In this paper, a new imaging modality, named photoacoustic resonance imaging (PARI), is proposed and experimentally demonstrated. Being distinct from conventional single nanosecond laser pulse induced wideband PA signal, the proposed PARI method utilizes multi-burst modulated laser source to induce PA resonant signal with enhanced signal strength and narrower bandwidth. Moreover, imaging contrast could be clearly improved than conventional single-pulse laser based PA imaging by selecting optimum modulation frequency of the laser source, which originates from physical properties of different materials beyond the optical absorption coefficient. Specifically, the imaging steps is as follows: 1: Perform conventional PA imaging by modulating the laser source as a short pulse to identify the location of the target and the background. 2: Shine modulated laser beam on the background and target respectively to characterize their individual resonance frequency by sweeping the modulation frequency of the CW laser source. 3: Select the resonance frequency of the target as the modulation frequency of the laser source, perform imaging and get the first PARI image. Then choose the resonance frequency of the background as the modulation frequency of the laser source, perform imaging and get the second PARI image. 4: subtract the first PARI image from the second PARI image, then we get the contrast-enhanced PARI results over the conventional PA imaging in step 1. Experimental validation on phantoms have been performed to show the merits of the proposed PARI method with much improved image contrast.
KEYWORDS: Signal to noise ratio, Photoacoustic spectroscopy, Signal detection, Optical filters, Electronic filtering, In vivo imaging, Photoacoustic imaging, Ultrasonography, Biomedical optics, Sensing systems
Sensitive detection is always crucial to photoacoustic sensing and imaging applications owing to the extremely low conversion efficiency from light to sound. Conventional approach to enhance the signal-to-noise ratio (SNR) of the photoacoustic signal is data averaging, which is quite time-consuming due to multiple data acquisitions for each photoacoustic measurement. Especially for high power pulsed laser source with only 10-20 pulse repetition rate, multiple data averaging will severely degrade the frame rate. In this paper, we present a simple but efficient way, called adaptive coherent photoacoustic (aCPA) sensing to obviously enhance the detected signal SNR with only single laser pulse. More specifically, The proposed aCPA employs an adaptive matched filter to cross-correlate with the raw time-domain PA signal iteratively. The optimum matched filter could be found after several iterations, leading to improved signal SNR. In vivo experimental results show that the proposed aCPA method improved the signal SNR by about 60 dB with single PA measurement. In conventional data averaging, 106 times PA measurements is required to achieve same SNR improvement. In other words, sensing and imaging speed is improved by 106 times in theory. It demonstrates the potential of aCPA to perform highly sensitive photoacoustic sensing and imaging with significantly accelerated speed.
Blood oxygen saturation (SO2) reflects the oxygenation level in blood transport and tissue. Previous studies have shown the capability of non-invasive quantitative measurements of SO2 by multi-wavelength photoacoustic (PA) spectroscopy for diagnosis of brain, tumor hemodynamics and other pathophysiological phenomena. However, those multi-wavelength methods require a tunable laser or multiple lasers which are relatively expensive and bulky for filed measurement environment and applications. Besides, the operation of multiple wavelengths, calibration procedures and data processing gets system complicated, which reduces the feasibility and flexibility for continuous real-time monitoring. Here we report a newly proposed method by combining PA and scattered light signals wherein imposing a hypothesis that scattering intensity is linear to the concentrations of oxygenated hemoglobin and deoxygenated hemoglobin weighed by blood scattering coefficients. A rigorous theoretical relationship between PA and scattering signals is thus established, making it possible that SO2 can be measured with only one excitation wavelength. To verify the theory basis, both dual-ink phantoms and fresh porcine blood sample have been employed in the experiments. The phantom experiment is able to quantify the concentration of mixed red-green ink that is in precise agreement with pre-set values. The ex vivo experiment with fresh porcine blood was conducted and the results of the proposed single-wavelength method achieved high accuracy of 1% - 4% errors. These demonstrated that the proposed single-wavelength SO2 detection is able to provide non-invasive, accurate measurement of blood oxygenation, and herein create potential for applying it to real clinical applications with low cost and high flexibility.
KEYWORDS: Nanoparticles, Magnetism, Temperature metrology, Imaging systems, Signal to noise ratio, Amplifiers, Electromagnetism, Signal generators, Transducers, Ultrasonography
Low frequency alternating magnetic field (AMF) had been advocated for thermoacoustic imaging to exploit their inherent deeper penetrations. AMF induced thermoacoustic imaging of magnetic nanoparticles is particularly appealing since the system setup is inherently compatible with nanoparticle hyperthermia therapy. More importantly, owing to the capacity of thermoacoustics for accurate temperature measurement, the integration of AMF induced thermoacoustic imaging into nanoparticle hyperthermia therapy will potentially enable a theranostic platform with imaging guidance and temperature monitoring capabilities. We present herein the AMF induced thermoacoustic process of magnetic nanoparticles experimentally and then investigate furthermore its utilization in temperature monitoring for the nanoparticle hyperthermia. To demonstrate the concept of an integrated theranostic system with minimal overhead, a single coil is used for both the hyperthermia heating and thermoacoustic imaging by interleaving the two processes in time domain. In thermoacoustic imaging mode, the power is set at the amplifier's maximum value whereas to avoid excess heating of the coil in hyperthermia-mode, the power is switched to a lower value and the coil is further cooled by static water. Phantom imaging results of the magnetic nanoparticles and the self temperature monitoring with sub-degree accuracy during hyperthermia process are demonstrated. These proof-of-concept experiments showcase the potential to integrate thermoacoustic imaging with nanoparticle hyperthermia system.
By “listening to photons,” photoacoustics allows the probing of chromosomes in depth beyond the optical diffusion limit. Here we report the photoacoustic resonance effect induced by multiburst modulated laser illumination, which is theoretically modeled as a damped mass-string oscillator and a resistor-inductor-capacitor (RLC) circuit. Through sweeping the frequency of multiburst modulated laser, the photoacoustic resonance effect is observed experimentally on phantoms and porcine tissues. Experimental results demonstrate different spectra for each phantom and tissue sample to show significant potential for spectroscopic analysis, fusing optical absorption and mechanical vibration properties. Unique RLC circuit parameters are extracted to quantitatively characterize phantom and biological tissues.
Phasoscopy is a recently proposed concept correlating electromagnetic (EM) absorption and scattering properties based on energy conservation. Phase information can be extracted from EM absorption induced acoustic wave and scattered EM wave for biological tissue characterization. In this paper, a novel imaging modality, termed photoacoustic phasoscopy (PAPS) imaging, is proposed and verified experimentally based on phasoscopy concept with laser illumination. Both endogeneous photoacoustic wave and scattered photons are collected simultaneously to extract the phase information, and phasoscopy image is then reconstructed by mapping phase distribution. The phasoscopy imaging experiments on vessel-mimicking phantom and ex vivo porcine tissues demonstrate significantly improved contrast than conventional photoacoustic imaging.
In this paper, alternating magnetic field is explored for inducing thermoacoustic effect on dielectric objects. Termed as magnetically mediated thermo-acoustic (MMTA) effect that provides a contrast in conductivity, this approach employs magnetic resonance for delivering energy to a desired location by applying a large transient current at radio frequency below 50MHz to a compact magnetically resonant coil. The alternating magnetic field induces large electric field inside conductive objects, which then undergoes joule heating and emanates acoustic signal thermo-elastically. The magnetic mediation approach with low radio frequency can potentially provide deeper penetration than microwave radiation due to the non-magnetic nature of human body and therefore extend thermoacoustic imaging to deep laid organs. Both incoherent time domain method that applies a pulsed radio frequency current and coherent frequency domain approach that employs a linear chirp signal to modulate the envelop of the current are discussed. Owing to the coherent processing nature, the latter approach is capable of achieving much better signal to noise ratio and therefore potential for portable imaging system. Phantom experiments are carried out to demonstrate the signal generation together with some preliminary imaging results. Ex-vivo tissue studies are also investigated.
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