arXiv subjects

Lihong V. Wang

Publications and source records attributed to Lihong V. Wang.

At least 37 records · Page 2Linked to original sources

arXiv2024

Functional photoacoustic noninvasive Doppler angiography in humans

Optical imaging of blood flow yields critical functional insights into the circulatory system, but its clinical implementation has typically been limited to shallow depths (~1 millimeter) due to light scattering in biological tissue. Here, we present photoacoustic noninvasive Doppler angiography (PANDA) for deep blood flow imaging. PANDA synergizes the photoacoustic and Doppler effects to generate color Doppler velocity and power Doppler blood flow maps of the vascular lumen. Our results demonstrate PANDA's ability to measure blood flow in vivo up to one centimeter in depth, marking approximately an order of magnitude improvement over existing high-resolution pure optical modalities. PANDA enhances photoacoustic flow imaging by increasing depth and enabling cross-sectional blood vessel imaging. We also showcase PANDA's clinical feasibility through three-dimensional imaging of blood flow in healthy subjects and a patient with varicose veins. By integrating the imaging system onto a mobile platform, we have designed PANDA to be a portable modality that is primed for expedient clinical translation. PANDA offers noninvasive, single modality imaging of hemoglobin and blood flow with three-dimensional capability, facilitating comprehensive assessment of deep vascular dynamics in humans.

physics.med-ph↗

arXiv2024

Score-Based Diffusion Models for Photoacoustic Tomography Image Reconstruction

Photoacoustic tomography (PAT) is a rapidly-evolving medical imaging modality that combines optical absorption contrast with ultrasound imaging depth. One challenge in PAT is image reconstruction with inadequate acoustic signals due to limited sensor coverage or due to the density of the transducer array. Such cases call for solving an ill-posed inverse reconstruction problem. In this work, we use score-based diffusion models to solve the inverse problem of reconstructing an image from limited PAT measurements. The proposed approach allows us to incorporate an expressive prior learned by a diffusion model on simulated vessel structures while still being robust to varying transducer sparsity conditions.

physics.med-ph↗

arXiv2023

Single-shot 3D photoacoustic computed tomography with a densely packed array for transcranial functional imaging

Photoacoustic computed tomography (PACT) is emerging as a new technique for functional brain imaging, primarily due to its capabilities in label-free hemodynamic imaging. Despite its potential, the transcranial application of PACT has encountered hurdles, such as acoustic attenuations and distortions by the skull and limited light penetration through the skull. To overcome these challenges, we have engineered a PACT system that features a densely packed hemispherical ultrasonic transducer array with 3072 channels, operating at a central frequency of 1 MHz. This system allows for single-shot 3D imaging at a rate equal to the laser repetition rate, such as 20 Hz. We have achieved a single-shot light penetration depth of approximately 9 cm in chicken breast tissue utilizing a 750 nm laser (withstanding 3295-fold light attenuation and still retaining an SNR of 74) and successfully performed transcranial imaging through an ex vivo human skull using a 1064 nm laser. Moreover, we have proven the capacity of our system to perform single-shot 3D PACT imaging in both tissue phantoms and human subjects. These results suggest that our PACT system is poised to unlock potential for real-time, in vivo transcranial functional imaging in humans.

physics.med-ph↗

arXiv2023

Numerical modeling of the multi-stage Stern$\unicode{x2013}$Gerlach experiment by Frisch and Segrè using co-quantum dynamics via the Bloch equation

We numerically study the spin flip in the Frisch$\unicode{x2013}$Segrè experiment, the first multi-stage Stern$\unicode{x2013}$Gerlach experiment, within the context of the novel co-quantum dynamics theory. We model the middle stage responsible for spin rotation by sampling the atoms with the Monte Carlo method and solving the dynamics of the electron and nuclear magnetic moments numerically according to the Bloch equation. Our results show that, without using any fitting parameters, the co-quantum dynamics closely reproduces the experimental observation reported by Frisch and Segrè in 1933, which has so far lacked theoretical predictions.

quant-ph↗

arXiv2023

Numerical modeling of the multi-stage Stern$\unicode{x2013}$Gerlach experiment by Frisch and Segrè using co-quantum dynamics via the Schrödinger equation

We use a theory termed co-quantum dynamics (CQD) to numerically model spin flip in the multi-stage Stern$\unicode{x2013}$Gerlach (SG) experiment conducted by R. Frisch and E. Segrè. This experiment consists of two Stern$\unicode{x2013}$Gerlach apparatuses separated by an inner rotation chamber that varies the fraction of spin flip. To this day, quantum mechanical treatments inadequately predict the Frisch$\unicode{x2013}$Segrè experiment. Here, we account for electron-nuclear interactions according to CQD and solve the associated Schrödinger equation. Our simulation outcome agrees with the Frisch$\unicode{x2013}$Segrè experimental observation and supports CQD as a potential model for electron spin evolution and collapse.

quant-ph↗

arXiv2023

Noninvasive in vivo photoacoustic measurement of internal jugular venous oxygenation in humans

In many clinical conditions, such as head trauma, stroke, and low cardiac output states, the brain is at risk for hypoxic-ischemic injury. The metabolic rate and oxygen consumption of the brain are reflected in internal jugular venous oxygen saturation (sijvO2). The current gold standard for monitoring brain oxygenation is invasive; it requires jugular vein catheterization under fluoroscopic guidance and therefore is rarely used. Photoacoustic (PA) measurement, on the other hand, can estimate the oxygen consumption of the brain non-invasively in real time. Such a convenient method can potentially aid earlier detection and prevention of impending hypoxic brain injury. A dual-wavelength photoacoustic tomography (PAT) and ultrasound imaging (US) system was used to image the internal jugular vein (IJV) and estimate the sijvO2 in seven healthy volunteers. The system captured simultaneous co-registered PAT and US images at a rate of five frames per second. For each volunteer, the internal jugular vein was identified under ultrasound guidance, then, additional PA images from two optical wavelengths were collected and used to estimate the oxygen saturation of the internal jugular vein. For each volunteer, the oxygen saturation was calculated from transverse and longitudinal views of the internal jugular vein. The average sijvO2 was 72 +/- 7 %. The preliminary results are encouraging and agree with those reported in the literature. Photoacoustic images were successfully used to calculate the blood hemoglobin oxygen saturation in the internal jugular vein. These results raise confidence that this emerging technology can be used clinically for accurate, noninvasive estimation of sijvO2. In addition, the fast co-registration with US images makes the technique suitable for studying the temporal variations of oxygen saturation in response to physiologic challenges in clinical settings.

physics.med-ph↗

arXiv2023

Quantification of cervical elasticity during pregnancy based on transvaginal ultrasound imaging and stress measurement

Objective: Strain elastography and shear wave elastography are two commonly used methods to quantify cervical elasticity; however, they have limitations. Strain elastography is effective in showing tissue elasticity distribution in a single image, but the absence of stress information causes difficulty in comparing the results acquired from different imaging sessions. Shear wave elastography is effective in measuring shear wave speed (an intrinsic tissue property correlated with elasticity) in relatively homogeneous tissue, such as in the liver. However, for inhomogeneous tissue in the cervix, the shear wave speed measurement is less robust. To overcome these limitations, we develop a quantitative cervical elastography system by adding a stress sensor to an ultrasound imaging system. Methods: In an imaging session for quantitative cervical elastography, we use the transvaginal ultrasound imaging system to record B-mode images of the cervix showing its deformation and use the stress sensor to record the probe-surface stress simultaneously. We develop a correlation-based automatic feature tracking algorithm to quantify the deformation, from which the strain is quantified. After each imaging session, we calibrate the stress sensor and transform its measurement to true stress. Applying a linear regression to the stress and strain, we obtain an approximation of the cervical Young's modulus. Results: We validate the accuracy and robustness of this elastography system using phantom experiments. Applying this system to pregnant participants, we observe significant softening of the cervix during pregnancy (p-value < 0.001) with the cervical Young's modulus decreasing 3.95% per week. We estimate that geometric mean values of cervical Young's moduli during the first (11 to 13 weeks), second, and third trimesters are 13.07 kPa, 7.59 kPa, and 4.40 kPa, respectively.

physics.med-ph↗

arXiv2023

Quantum imaging of biological organisms through spatial and polarization entanglement

Quantum imaging can potentially provide certain advantages over classical imaging. Thus far, however, the signal-to-noise ratios (SNRs) are poor; the resolvable pixel counts are low; biological organisms have not been imaged; birefringence has not been quantified. Here, we introduce quantum imaging by coincidence from entanglement (ICE). Utilizing spatially and polarization entangled photon pairs, ICE exhibits higher SNRs, greater resolvable pixel counts, imaging of biological organisms, and ghost birefringence quantification; it also enables 25 times greater suppression of stray light than classical imaging. ICE can potentially empower quantum imaging towards new applications in life sciences and remote sensing.

quant-ph↗

arXiv2022

Photoacoustic vector tomography for deep hemodynamic imaging

Non-invasive imaging of deep blood vessels for mapping hemodynamics remains an open quest in biomedical optical imaging. Although pure optical imaging techniques offer rich optical contrast of blood and have been reported to measure blood flow, they are generally limited to surface imaging within the optical diffusion limit of about one millimeter. Herein, we present photoacoustic vector tomography (PAVT), breaking through the optical diffusion limit to image deep blood flow with speed and direction quantification. PAVT synergizes the spatial heterogeneity of blood and the photoacoustic contrast; it compiles successive single-shot, wide-field photoacoustic images to directly visualize the frame-to-frame propagation of the blood with pixel-wise flow velocity estimation. We demonstrated in vivo that PAVT allows hemodynamic quantification of deep blood vessels at five times the optical diffusion limit (more than five millimeters), leading to vector mapping of blood flow in humans. By offering the capability for deep hemodynamic imaging with optical contrast, PAVT may become a powerful tool for monitoring and diagnosing vascular diseases and mapping circulatory system function.

physics.med-ph↗

arXiv2022

Transcranial photoacoustic computed tomography of human brain function

Herein we report the first in-human transcranial imaging of brain function using photoacoustic computed tomography. Functional responses to benchmark motor tasks were imaged on both the skull-less and the skull-intact hemispheres of a hemicraniectomy patient. The observed brain responses in these preliminary results demonstrate the potential of photoacoustic computed tomography for achieving transcranial functional imaging.

physics.med-ph↗

arXiv2020

Learning-based super interpolation and extrapolation for speckled image reconstruction

Speckles arise when coherent light interacts with biological tissues. Information retrieval from speckles is desired yet challenging, requiring understanding or mapping of the multiple scattering process, or reliable capability to reverse or compensate for the scattering-induced phase distortions. In whatever situation, insufficient sampling of speckles undermines the encoded information, impeding successful object reconstruction from speckle patterns. In this work, we propose a deep learning method to combat the physical limit: the sub-Nyquist sampled speckles (~14 below the Nyquist criterion) are interpolated up to a well-resolved level (1024 times more pixels to resolve the same FOV) with smoothed morphology fine-textured. More importantly, the lost information can be retraced, which is impossible with classic interpolation or any existing methods. The learning network inspires a new perspective on the nature of speckles and a promising platform for efficient processing or deciphering of massive scattered optical signals, enabling widefield high-resolution imaging in complex scenarios.

eess.IV↗

arXiv2017

A forward-adjoint operator pair based on the elastic wave equation for use in transcranial photoacoustic tomography

Photoacoustic computed tomography (PACT) is an emerging imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the photoacoustically induced initial pressure distribution within tissue. The PACT reconstruction problem corresponds to an inverse source problem in which the initial pressure distribution is recovered from measurements of the radiated wavefield. A major challenge in transcranial PACT brain imaging is compensation for aberrations in the measured data due to the presence of the skull. Ultrasonic waves undergo absorption, scattering and longitudinal-to-shear wave mode conversion as they propagate through the skull. To properly account for these effects, a wave-equation-based inversion method should be employed that can model the heterogeneous elastic properties of the skull. In this work, a forward model based on a finite-difference time-domain discretization of the three-dimensional elastic wave equation is established and a procedure for computing the corresponding adjoint of the forward operator is presented. Massively parallel implementations of these operators employing multiple graphics processing units (GPUs) are also developed. The developed numerical framework is validated and investigated in computer-simulation and experimental phantom studies whose designs are motivated by transcranial PACT applications.

physics.med-ph↗

arXiv2017

Mitigation of artifacts due to isolated acoustic heterogeneities in photoacoustic computed tomography using a variable data truncation-based reconstruction method

Photoacoustic computed tomography (PACT) is an emerging computed imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the absorbed optical energy density within tissue. If the object possesses spatially variant acoustic properties that are unaccounted for by the reconstruction method, the estimated image can contain distortions. While reconstruction methods have recently been developed to compensate for this effect, they generally require the object's acoustic properties to be known a priori. To circumvent the need for detailed information regarding an object's acoustic properties, we previously proposed a half-time reconstruction method for PACT. A half-time reconstruction method estimates the PACT image from a data set that has been temporally truncated to exclude the data components that have been strongly aberrated. However, this method can be improved upon when the approximate sizes and locations of isolated heterogeneous structures, such as bones or gas pockets, are known. To address this, we investigate PACT reconstruction methods that are based on a variable data truncation (VDT) approach. The VDT approach represents a generalization of the half-time approach, in which the degree of temporal truncation for each measurement is determined by the distance between the corresponding ultrasonic transducer location and the nearest known bone or gas void location. Computer-simulated and experimental data are employed to demonstrate the effectiveness of the approach in mitigating artifacts due to acoustic heterogeneities.

physics.med-ph↗

arXiv2016

Sub-Nyquist sampling boosts targeted light transport through opaque scattering media

Optical time-reversal techniques are being actively developed to focus light through or inside opaque scattering media. When applied to biological tissue, these techniques promise to revolutionize biophotonics by enabling deep-tissue non-invasive optical imaging, optogenetics, optical tweezers and photodynamic therapy. In all previous optical time-reversal experiments, the scattered light field was well-sampled during wavefront measurement and wavefront reconstruction, following the Nyquist sampling criterion. Here, we overturn this conventional practice by demonstrating that even when the scattered field is under-sampled, light can still be focused through or inside opaque media. Even more surprisingly, we show both theoretically and experimentally that the focus achieved by under-sampling is usually about one order of magnitude brighter than that achieved by conventional well-sampling conditions. Moreover, sub-Nyquist sampling improves the signal-to-noise ratio and the collection efficiency of the scattered light. We anticipate that this newly explored under-sampling scheme will transform the understanding of optical time reversal and boost the performance of optical imaging, manipulation, and communication through opaque scattering media.

physics.bio-ph↗

arXiv2015

Joint Reconstruction of Absorbed Optical Energy Density and Sound Speed Distribution in Photoacoustic Computed Tomography: A numerical Investigation

Photoacoustic computed tomography (PACT) is a rapidly emerging bioimaging modality that seeks to reconstruct an estimate of the absorbed optical energy density within an object. Conventional PACT image reconstruction methods assume a constant speed-of-sound (SOS), which can result in image artifacts when acoustic aberrations are significant. It has been demonstrated that incorporating knowledge of an object's SOS distribution into a PACT image reconstruction method can improve image quality. However, in many cases, the SOS distribution cannot be accurately and/or conveniently estimated prior to the PACT experiment. Because variations in the SOS distribution induce aberrations in the measured photoacoustic wavefields, certain information regarding an object's SOS distribution is encoded in the PACT measurement data. Based on this observation, a joint reconstruction (JR) problem has been proposed in which the SOS distribution is concurrently estimated along with the sought-after absorbed optical energy density from the photoacoustic measurement data. A broad understanding of the extent to which the JR problem can be accurately and reliably solved has not been reported. In this work, a series of numerical experiments is described that elucidate some important properties of the JR problem that pertain to its practical feasibility. To accomplish this, an optimization-based formulation of the JR problem is developed that yields a non-linear iterative algorithm that alternatingly updates the two image estimates. Heuristic analytic insights into the reconstruction problem are also provided. These results confirm the ill-conditioned nature of the joint reconstruction problem that will present significant challenges for practical applications.

physics.med-ph↗

arXiv2015

Fast binarized time-reversed adapted-perturbation (b-TRAP) optical focusing inside scattering media

Light scattering inhibits high-resolution optical imaging, manipulation and therapy deep inside biological tissue by preventing focusing. To form deep foci, wavefront-shaping and time-reversal techniques that break the optical diffusion limit have been developed. For in vivo applications, such focusing must provide high gain, high speed, and a large number of spatial modes. However, none of the previous techniques meet these requirements simultaneously. Here, we overcome this challenge by rapidly measuring the perturbed optical field within a single camera exposure followed by adaptively time-reversing the phase-binarized perturbation. Consequently, a phase-conjugated wavefront is synthesized within a millisecond, two orders of magnitude shorter than the digitally achieved record. We demonstrated real-time focusing in dynamic scattering media, and extended laser speckle contrast imaging to new depths. The unprecedented combination of fast response, high gain, and large mode count makes this work a major stride toward in vivo deep tissue optical imaging, manipulation, and therapy.

physics.optics↗

arXiv2015

A constrained variable projection reconstruction method for photoacoustic computed tomography without accurate knowledge of transducer responses

Photoacoustic computed tomography (PACT) is an emerging computed imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the absorbed optical energy density within tissue. When the imaging system employs conventional piezoelectric ultrasonic transducers, the ideal photoacoustic (PA) signals are degraded by the transducers' acousto-electric impulse responses (EIRs) during the measurement process. If unaccounted for, this can degrade the accuracy of the reconstructed image. In principle, the effect of the EIRs on the measured PA signals can be ameliorated via deconvolution; images can be reconstructed subsequently by application of a reconstruction method that assumes an idealized EIR. Alternatively, the effect of the EIR can be incorporated into an imaging model and implicitly compensated for during reconstruction. In either case, the efficacy of the correction can be limited by errors in the assumed EIRs. In this work, a joint optimization approach to PACT image reconstruction is proposed for mitigating errors in reconstructed images that are caused by use of an inaccurate EIR. The method exploits the bi-linear nature of the imaging model and seeks to refine the measured EIR during the process of reconstructing the sought-after absorbed optical energy density. Computer-simulation and experimental studies are conducted to investigate the numerical properties of the method and demonstrate its value for mitigating image distortions and enhancing the visibility of fine structures.

physics.med-ph↗

arXiv2014

Tracking and imaging of dynamic objects in scattering media by time-reversed adapted-perturbation (TRAP) optical focusing

The ability to steer light propagation inside scattering media has long been sought-after due to its potential widespread applications. To form optical foci inside scattering media, the only feasible strategy is to guide photons by using either implanted or virtual guide stars. However, all of these guide stars must be introduced extrinsically, either invasively or by physical contact, limiting the scope of their application. Here, we focus light inside scattering media by employing intrinsic dynamics as guide stars. By time-reversing the perturbed component of the scattered light adaptively, we concentrate light to the origin of the perturbation, where the permittivity varied spontaneously. We demonstrate dynamic light focusing onto moving targets and imaging of a time-variant object obscured by highly scattering media, without invasiveness and physical contact. Anticipated applications include all-weather optical communication with airplanes or satellites, tracking vehicles in thick fogs, and imaging and photoablation of angiogenic vessels in tumors.

physics.optics↗