This Conference Presentation, Deep learning and photoacoustic image formation: promises and challenges, was recorded at Photonic West 2023 held in San Francisco, CA, United States.

This Conference Presentation, Sound of light: optoacoustic vs. optical imaging, was recorded at Photonic West 2023 held in San Francisco, CA, United States.

This Conference Presentation, Non-genetic photoacoustic neural stimulation, was recorded at Photonic West 2023 held in San Francisco, CA, United States.

This work presents initial findings from the first-in-the world clinical trial examining the feasibility of photoacoustic imaging for assessing the quality of kidney transplants.

Ionizing radiation acoustic imaging (iRAI) provides the potential to map the radiation dose during radiotherapy in real time. Described here is our recent development of an iRAI volumetric imaging system in mapping the three-dimensional (3D) radiation dose deposition of a complex clinical radiotherapy treatment plan. Temporal 3D dose accumulation of a treatment plan was first imaged in a phantom. Then, semi-quantitative iRAI measurements were verified with rabbit liver model in vivo. Finally, for the first time, real-time visualization of radiation dose delivered deep in a patient with liver metastases was successfully performed. These studies demonstrate the potential of iRAI to map the dose distribution in deep body during radiotherapy, potentially leading to personalized radiotherapy with optimal efficacy and safety.

In this study, we developed a prototype interstitial all-optical needle photoacoustic sensing probe for clinical translation of prostate cancer. The performance of the PA needle probe was examined on intact human prostates ex vivo to simulate the transrectal ultrasound (US) guided transperineal prostate biopsy procedures. Analysis based on PA spectrum analysis in 8-28 MHz range of acquired RF signals at multi-wavelengths shows statistical difference between benign and cancerous regions (n=49, p<0.05). Multivariate SVM analysis using linear and midbandfit parameters can obtain an accuracy close to 90%.

IPASC organized a roadmapping exercise in 2022 encompassing over 50 participants, which identified eight barriers to clinical translation of PAI: 1) scientific and technological limitations; 2) gaps between technological push and clinical pull; 3) lack of interface with existing standards; 4) poor uptake of phantoms; 5) limited community outreach; 6) poor complementarity of animal models with clinical testing; 7) translation of data-driven methods; and 8) quantitative photoacoustics. Participants defined the scope of each barrier and compared the current state against envisioned goals and outcomes. The resulting roadmaps that define IPASC deliverables in standards development and community engagement will be presented.

We present results of rectal cancer treatment response assessment using co-registered ultrasound and photoacoustic imaging from over 20 in vivo patients. We develop a deep learning model based on co-registered dual-modality images with individualized prior information. Compared to models using only ultrasound images, our model identifies complete treatment responders with significantly higher accuracy. We achieve a 3-class classification accuracy (normal, cancer, and image artifact) of 89.1±0.8%. To facilitate surgeons’ decision-making, we generate localized hotspots to indicate suspicious cancer regions based on model predictions. We conclude that the addition of photoacoustic imaging to conventional ultrasound improves treatment response assessment.

A 3D high resolution Fabry Perot photoacoustic scanner has been developed for clinical use. The system now employs a novel 64-channel optical scanning architecture and compressed sensing methods providing up to three orders of magnitude faster acquisition than previous pre-clinical embodiments. To demonstrate the rapid, high quality volumetric imaging capabilities, and the versatility of the scanner, images from different regions of the body that are known to exhibit distinctive vascular anatomy were acquired using healthy volunteers as participants. In addition, to illustrate potential clinical applicability, imaging studies of patients suffering from diseases characterised by abnormal vascular anatomy were conducted.

In OAT breast imaging, the optical fluence distribution in the breast under the skin layer is influenced by the melanin concentration in the epidermis. However, the extent to which skin color affects the ability to detect lesions and estimate physiological parameters in OAT breast imaging remains relatively unexplored. To address this, for the first time, realistic virtual imaging studies were conducted to assess the impact of skin color on 3D breast OAT. These studies quantitatively revealed the extent to which skin color diminishes the optical fluence within breast tissue and degrades the signal-to-noise ratio of lesions at various depths.

Fabry-Perot (FP) ultrasound sensors are widely used for Photoacoustic Tomography (PAT), affording high resolution (<100 μm) images, with a penetration depth of about 1 cm, limited by system's sensitivity. The sensitivity is, in turn, limited by the shape of the Gaussian beam typically used to interrogate the FP sensor, which is not well "confined" inside the FP cavity. To overcome this limitation, a novel PAT system employing Bessel beam to interrogate the FP sensor was prototyped. Unlike Gaussian beams, Bessel beams are well confined in the FP cavity, increasing the system's sensitivity by multiple orders of magnitude, paving the way to multi-centimetre clinical PAT imaging with high resolution

To extend the depth of field (DOF) in optical-resolution photoacoustic microscopy (OR-PAM), we propose the needle-shaped beam photoacoustic microscopy (NB-PAM) via customized diffractive optical elements to extend the DOF, featuring a well-maintained beam diameter, a uniform axial intensity distribution, and negligible sidelobes. The advantage of using NB-PAM with an improved DOF has been demonstrated by both histology-like imaging of fresh slide-free organs using 266 nm laser and in vivo mouse brain vasculature imaging using 532 nm laser. Our approach provides new perspectives for slide-free intraoperative pathological imaging and various in vivo organ-level imaging applications.

In adoptive cell therapy (ACT) of solid tumors, only a small fraction of T cells typically accumulates at the target. Therefore, methods to noninvasively assess adoptive T cell infiltration are critical for ACT success. Here we present an approach based on photoacoustic (PA) and ultrasound (US) imaging to visualize nanoparticle (NP)-tagged adoptive T cells within tumor region. Our results indicate feasibility of the T cell tagging with NPs and US/PA imaging of adoptive T cells with clinically relevant spatial resolution and imaging depth thus providing critical imaging feedback to expedite development, translation, and expansion of ACT.

We present the developments on a simple multiple-view dual-mode photoacoustic/ultrasound system for in-vivo, non-invasive, whole-body small-animal imaging and based on planar Fabry-Pérot sensor-based tomography systems to overcome present challenges. Single planar Fabry-Pérot sensors suffer from an incomplete view of the acoustic fields, which leads to blurring and artefacts in tissue sample images. Increasing the fields of view would relax this limitation. Another contribution to the degradation of the image quality are wavefront aberrations stemming from spatially-varying sound speeds in a tissue sample and which limit the imaging depth. These can however be corrected by carrying out ultrasound computed tomography.

In vivo imaging of blood flow is the key for mapping circulatory system function. While photoacoustic computed tomography (PACT) is well-established for imaging deep blood vessels, its feasibility for measuring blood flow beyond the optical diffusion limit (one millimeter) has not been demonstrated. Herein, we report, to our knowledge, the first use of PACT to image deep blood flow in humans. We achieved a penetration depth greater than five millimeters and obtained both the speed and direction as a vector flow map. This work establishes PACT as a powerful tool to study the rich contrast of blood and its hemodynamics.

In this work, we evaluated the acoustic and optical properties of silk protein-based hydrogels to investigate its potential as a phantom material. Acoustic properties include the speed of sound and acoustic attenuation of silk scaffolds at various concentrations. Optical properties include optical absorption and reduced scattering measured between 400 nm to 1200 nm to coincide with common photoacoustic imaging bandwidths. The results indicate that silk is an acceptable phantom material for ultrasound and photoacoustic systems as it inherently displays similar acoustic properties and reduced scattering as various tissue types while displaying low absorption.

To understand the stability of photoacoustic imaging for longitudinal imaging, a repeatability study needs to be performed. In longitudinal imaging, instrumental drifts or other changes over time, are likely to affect images in complex ways. In this study, inter- and intra-day variations of the photoacoustic-ultrasound breast imager are measured with a specially developed test phantom as ground truth. The phantom mimics the breast temperature to be able to measure the coupling medium’s temperature stability and homogeneity in a as realistic as possible setting. Moreover, photoacoustic targets are used to measure the pressure correlated to the pulse-by-pulse laser output energy.

Presented here is an application of the new approach of chemical imaging, performing an in-vivo chemical analysis, to predict a given tumor’s response to radiation therapy. Cancer tumors’ oxygen distributions in PDX mice was imaged by photoacoustic imaging with tumor-targeted oxygen sensor nanoparticles. Following radiation therapy, we established a quantitatively significant correlation between the spatial distribution of the initial oxygen levels and the spatial distribution of the therapy’s efficacy: the higher the local oxygen, the higher the local radiation therapy efficacy. The presented cancer chemical imaging provides a non-invasive method to predict the efficacy of radiotherapy for a given tumor.

We developed an indocyanine green J-aggregated (ICG-JA) nanoparticle platform for near infrared photoacoustic imaging (NIR-PAI). This platform achieves a facile synthesis, size tunability and direct functionalization. In an in vitro setting, we compared the PA signal of ICG-JA (at its optical absorption peak of 895 nm) to be two times that of whole blood. We then imaged HeLa cells with ICG-JA functionalized with RGD-peptide using NIR-PAI. Using a multi-wavelength NIR-PAI system, TriTom™, volumetric whole-body images were acquired of mice administed with RGD-peptide functionalized ICG-JA. Results indicated enhanced visualization of the liver, spleen and thoracic arteries with a contrast-to-noise-ratio of 2.42.

Polymer-based nanoparticles are promising contrast agents for photoacoustic (PA) imaging as their properties can be tailored to maximize detection sensitivity against the overwhelming endogenous background, while pump-probe excitation and fluence-dependent image acquisition may provide alternative approaches for contrast agent detection instead of multispectral imaging and unmixing. In this study, PA signals were measured in single-chain nanoparticle (SCNP) suspensions at pump and probe wavelengths of 690 nm and 730 nm and showed a strong nonlinear fluence dependence, which provides a unique contrast mechanism for molecular PA imaging.

Stromal cells play an active role in tumor proliferation, invasion, and metastasis. Fibroblast is a common stromal cell that aids in the production of collagen. Collagen accumulation in the tumor can result in squeezing blood vessels and reducing treatment efficiency. In this work, we present photoacoustic imaging of tumor stroma, analyzing the blood and collagen content. We imaged tumors from two small animal groups, one induced with tumor cells alone and another with tumor cells and fibroblast cells. Our results show significant differences in blood and collagen content in these two tumor types highlighting the effect of tumor stroma.

Quantification of fibrosis is critical for the management of inflammatory bowel disease. In this study, two measurements, collagen-to-Hb ratio quantified by spectroscopic analysis and tissue stiffness quantified by PA-strain, measured by our PA-US balloon catheter were employed to quantify intestinal fibrosis in 23 rabbits in vivo. Results show that both measurements can distinguish the low histological fibrosis (0-2) and high histological fibrosis (3-5) with statistical significance (p-value<0.001). Collagen-to-Hb ratio and PA-strain are highly correlated with the fibrosis stages with correlation of 0.67 and 0.64, respectively. PA-strain is positively correlated to Young’s Modulus measured ex vivo using microelastometer with correlation 0.81.

We developed an open-source python toolkit for photoacoustic image (PAI) reconstruction and processing. The toolkit implements GPU-accelerated processing algorithms including preprocessing, image reconstruction (backprojection and model-based) and multispectral analysis (linear spectral unmixing and learned spectral decolouring). We implemented methods for the advanced analysis of longitudinal PA data, including standardised analysis of oxygen-enhanced and dynamic contrast enhanced MSOT data. The toolkit currently works with pre-clinical, clinical and simulated PA systems, integrating with the IPASC open data format, simulated datasets from the SIMPA toolkit and iThera Medical MSOT devices. It can easily be extended to support other algorithms and systems.

Non-alcoholic fatty liver disease (NAFLD) starts with the accumulation of lipids in liver tissues before progressing into liver cirrhosis and hepatocellular carcinoma. Transmission-reflection optoacoustic ultrasound (TROPUS) can simultaneously interrogate biological tissues with three ultrasound-based imaging modalities based on different contrast mechanisms. We propose TROPUS imaging for the assessment of NAFLD in vivo and ex vivo. Multispectral optoacoustic tomography resolves the oxy- and deoxy-hemoglobin, lipid and melanin content in the tissues. Reflection ultrasound computed tomography facilitates segmenting the liver by providing anatomical information. Transmission ultrasound computed tomography quantifies changes in speed of sound due to lipid accumulation.

This work presents a novel method for performing respiratory corrections for photoacoustic imaging of kidney and liver oxygenation and collagen.

Delay-and-sum beamformation (DAS), i.e., back-projection is the most common PAI image reconstruction algorithm. Here we propose a novel PAI image reconstruction technique – hyper-beamformation (HBF), which reaches significantly low sidelobes compared with DAS, outperforms delay-multiply-and-sum (DMAS) with lower complexity, and offers tunability on lateral resolution, precision, and contrast. Via the subtraction of the beam-pattern difference of the left and right sub-arrays from their beam-pattern sum, a hyper beam with narrow mainlobe, low sidelobes, and suppressed grating-lobe artifact can be obtained. Experimental results show that our proposed HBF has significant improvement on precision and contrast.

IPASC has initiated the creation of an open-source library for image reconstruction algorithms that are compatible with the IPASC data format. The goals of the project are to: (1) create a testing framework for evaluation of newly developed image reconstruction algorithms to identify their context-dependent strengths and weaknesses; (2) enable insight into algorithm behavior under different conditions; (3) develop an open-access dataset comprising both simulated and experimental data; (4) facilitate collaboration among all stakeholders associated with photoacoustic imaging; and (5) accelerate developments in the field by making the project deliverables available open-source, lowering the barrier of entry for new researchers.

Optoacoustics (OA) is overwhelmingly implemented in the Time Domain (TD) to achieve high signal-to-noise ratios (SNR) by maximizing the excitation light energy transient. Implementations in the Frequency Domain (FD) have been proposed, but suffer from low SNR and have not offered competitive advantages over TD methods. It is therefore commonly believed that TD is the optimal way to perform optoacoustics. Here we introduce an optoacoustic concept based on pulse train illumination and FD multiplexing and theoretically demonstrate the superior merits of the approach compared to the TD. Then, using recent advances in laser diode illumination, we launch Frequency Wavelength Multiplexing Optoacoustic Tomography (FWMOT), at multiple wavelengths, and experimentally showcase how FWMOT optimizes the SNR of spectral measurements over TD methods in phantoms and in vivo. We further find that FWMOT offers the fastest multi-spectral operation ever demonstrated in optoacoustics.

IPASC has recently published a data format through a consensus-based process which includes a defined metadata structure that describes: (1) PAI system design parameters such as the illumination and detection geometry; (2) container format metadata; and (3) data acquisition including the optical wavelengths, sampling frequency, or timestamps. The container format is designed to store time-series data and internal quality control mechanisms are included to ensure completeness and consistency. Furthermore, a Python-based open-source software application programming interface (API) was developed to facilitate using the IPASC data format and we aim to partner with prospective users to make improvements.

Localization optoacoustic tomography (LOT) can significantly enhance the optoacoustic imaging capabilities by providing a spatial resolution beyond the acoustic diffraction barrier and further enabling mapping the blood flow velocity. Higher resolution results in an enhanced sensitivity to cardiac and breathing motion, which can degrade the LOT imaging performance even if the animal is constrained. We suggest a new approach based on aligning the motion-affected frames of the acquired sequence with a reference frame. Localization and tracking of particles is then performed in the corrected sequence. This results in an enhanced imaging performance and more accurate velocity readings.

The most clinically compatible PAT configuration usually employs a linear ultrasound array, which often has a limited detection view and poor image fidelity. Exogenous contrast agents such as nanoparticles can be employed but lacks clinical translation potential. We have developed a new methodology by using clinically-approved microbubble as virtual point sources that strongly scatter the local pressure waves from surround hemoglobin, preserving PAT’s functional capability and clinical translation potential. We can overcome the limited-detection-view problem and achieve high-fidelity functional PAT in deep tissue. We have investigated the working principle and demonstrated proof-of-concept applications using simulations, phantoms, and in vivo small-animal studies.

Detailed vasculature imaging is a critical tool for understanding tissue health especially for applications in cancer and ophthalmic diagnostics. Photoacoustic remote sensing (PARS), a novel imaging technology, has previously been successfully applied for both structural and functional imaging of vasculature including in dermatologic and ophthalmic imaging while remaining non-contact and label-free. To provide better molecular specificity, this work demonstrates a total-absorption PARS imaging system which incorporates sensitivity to both non-radiative and radiative contrast. This additional contrast enables more advanced molecular unmixing (e.g. between melanin, hemoglobin, and oxyhemoglobin) which will prove essential for all PARS vasculature imaging systems.

Demonstrations of acousto-optic effects in fluorescent samples are widespread but their utility is generally limited due to the small amplitude modulations achievable and concurrently, long acquisition times. Here, we report the observation of a novel, gigantic acousto-optic modulation of two-photon excited fluorescence. The effect’s magnitude when applying low intensity ultrasound allows high SNR modulation of fluorescence in standard multiphoton systems without sophisticated detection schemes and without the need for extensive temporal averaging or signal processing. We observe this effect in the brain of awake behaving mice, demonstrating its utility for future advanced AO applications in vivo.

Acousto-Optics (AO) imaging is a bimodal imaging technique which couples ultrasounds (US) to Infrared (IR) light inside a scattering medium. The photons which paths cross with a controlled MHz-ultrasound pulse undergo the acousto-optic effect, resulting in the frequency shift that can be selectively detected using holography-based detection methods. The spatio-temporal profile of US is crucial in the imaging step, and various approaches from direct imaging using focused US to indirect imaging using plane waves have been described in the literature. Here, we present an indirect imaging approach designated as Fourier-Transform Acousto-Optic (FTAO). The technique is based on digital holography for the detection of tagged photons. In FTAO, long-lasting US pulses are spatio-temporally structured in order to fetch the Fourier components of the AO image. We present an integrated setup where images at acquired at video rate and fully compabtible with the constraints of in-vivo imaging.

We present an experimental ischemic stroke study using our newly-developed multimodal imaging system that integrates photoacoustic computed tomography (PACT), high-frequency ultrasound imaging, and acoustic angiographic tomography, or PAUSAT. PAUSAT is capable of three-dimensional high-frequency ultrasound imaging of the brain morphology, micro-bubble-enabled acoustic angiography of the brain blood perfusion, and multispectral PACT of brain blood oxygenation. PAUSAT was able to clearly show the brain vascular changes after ischemic stroke, including significantly reduced blood perfusion and oxygenation. Using PAUSAT, stroke infarct volume was reliably measured. The PAUSAT results were confirmed by laser speckle imaging and histology.

As medical advances allow the maternal age to rise, the risk of ectopic calcification and placental vascular dysfunction increases, both associated with preeclampsia. We investigated Slc20a2 mice models through non-invasive commercial ultrasound and photoacoustic imaging. This model exhibits increased ectopic placental vascular calcification, reduced fetal growth, and decreased postnatal bone mineral density. Our experiments established a significant difference in both placental function and structural differences between normal and diseased placentas. Dual-wavelength images and radio frequency data provided oxygen saturation and quantitative ultrasound spectral parameters that proved the control placentas can be distinguished from knockout placentas.

Portable LED-based systems attempt to replace the bulky laser-based photoacoustic (PA) systems. The problem with LEDs is their low energy which generates low signal-to-noise-ratio (SNR) images. To obtain a high SNR image in real-time, we built a deep learning U-net model which transforms a low no. of frame-averaged image into a high no. of frame-averaged quality image. Both laser-based Vevo LAZR-X system and immunofluorescence histology staining show similar vascular organizations with hypoxic cores. We also achieved high SNR by running the algorithm on acoustic-resolution PA microscopy captured images. This generic network can be implemented in multiple scenarios.

Our study exploits Rhodopseudomonas palustris BphP1 bacterial phytochrome to generate a near-infrared (NIR) loxP-BphP1 photoswitchable transgenic mouse model that enables deep-tissue optogenetics and photoacoustic tomography (PAT). BphP1 incorporates biliverdin and reversibly switches between the ground state and activated state, with distinct optical absorption spectra in the NIR window. We validated the optogenetic performance of the BphP1-encoded mouse model to trigger gene transcription, and demonstrated its superior capability of deep-tissue optogenetics. Then, taking advantage of BphP1's photoswitching properties, we can suppress the non-switching signals from background blood and improve the molecular detection sensitivity of PAT by three orders of magnitude.

In this study, we developed a label-free photoacoustic computed tomography system to monitor the visually-evoked hemodynamic changes in response to retinal photostimulation by flickering white light. The acoustic signals were collected by a 256-element linear ultrasound transducer array with a 10MHz central frequency, and a 750nm pulsed laser with a 10Hz repetition rate was used as the excitation source to avoid stimulating retinal photoreceptors. During the stimulation, the hemodynamic responses within the visual regions, such as the primary visual cortex, superior colliculus, and suprachiasmatic nucleus, have been observed. This demonstrates that our system can examine visually-evoked brain responses, and has the potential to study the brain activities in mouse models of retinal diseases.

Reliable and more accessible biomarkers along with advanced imaging methods are essential for early diagnosis to achieve effective therapeutic interventions of Alzheimer's disease (AD). In this study, an integrated photoacoustic microscopy (PAM) and optical coherence tomography (OCT) dual-modality ocular biomarkers imaging system was developed, and its performance was evaluated with an Alzheimer's disease mouse model. The beta amyloid deposition in retinal microvasculature were imaging by dual-wavelength PAM with near-infrared absorbing gold nanochains conjugated with anti-beta amyloid antibodies. The multi-layer retinal structure changes were investigated via OCT. With the unique ability of imaging the multiple ocular biomarkers via a single scan, the proposed system provides a new tool for investigating AD in animal models.

A longitudinal study on both 3D and 2D photoacoustic and Doppler ultrasound images of rat leg rheumatoid arthritis development has been performed using an automatic imaging system based on a GE HealthCare VividTM E95 unit with a L8-18i-D probe, an OPOTEK tunable laser system, and a Universal Robots UR3 robotic arm. Daily imaging of ankle bones was performed starting from day 0 when the lyophilized Mycobacterium butyricum was injected to induce the disease. Although both photoacoustic and Doppler ultrasound can confirm the disease development, photoacoustic imaging is more sensitive to microvasculature and enables earlier detection of inflammation than Doppler ultrasound.

Here, we assess the capabilities of photoacoustic imaging (PAI) biomarkers to shed light into perfusion-limited hypoxia, a key driver of tumor malignancy. Using two breast cancer xenograft models, we found that photoacoustic tomography could detect higher fluctuations in oxygen saturation (sO2MSOT) in models with higher disease aggressiveness, supported by an overall lower sO2MSOT and greater spatial heterogeneity in sO2MSOT. Photoacoustic mesoscopy revealed differences in vascular architecture and perfusion dynamics between the models. The results were validated using immunohistochemistry and RNA sequencing, highlighting the potential of PAI to provide non-invasive insight on dynamic phenomena associated with perfusion-limited hypoxia in vivo.

Optoacoustic tomography (OAT) in the first near infrared window (NIR I) can capture much of the mouse brain with high temporal and spatial (mesoscale) resolutions, making it an excellent candidate for functional neuroimaging studies. Here, we introduce and demonstrate two complementary advances in this emerging technology: functional OAT neuro-imaging in awake, head-fixed mice and simultaneous imaging of the real time dynamics of both the vascular and glymphatic systems. We demonstrate our system’s new capabilities by imaging functional responses to odor stimuli throughout the olfactory system and characterizing brain-wide clearance dynamics.

Traditional deconvolution methods can improve the spatial resolution of photoacoustic computed tomography (PACT) systems but are often sensitive to noise. We propose a novel approach to enhance the resolution of PACT, by modeling the system’s point spread function (PSF) and performing deep-learning-based deconvolution. We train a robust deep learning model without the need for ground truth, using a self-supervised method on a mixed dataset of simulation, phantom, and in vivo data, in combination with various data augmentation techniques. We demonstrate that our deep learning deconvolution achieves superior spatial resolution, image contrast, and artifact suppression, when compared to traditional deconvolution methods.

Machine learning-based approaches have shown promise for quantitative photoacoustic oximetry, however, the impact of learned methods is hampered by challenges of usability and generalisability, caused by the strong dependence of learned methods on the training data sets. To address these issues we developed a deep learning-based approach with higher flexibility. The method is trained on a suite of training data sets representing a range of general assumptions. The performance is systematically compared to linear unmixing methods and is validated on in silico, in vitro, and in vivo data representing different use cases.

Significant efforts are being made to reduce histology turnaround times. Total-Absorption Photoacoustic Remote Sensing (TA-PARS) is the first independent all-optical, label-free optical microscope to provide radiative and non-radiative absorption and optical scattering in a single acquisition. Such array of contrasts enables TA-PARS to rapidly capture most diagnostic elements. Here, a deep learning model, Pix2Pix, is trained within an end-to-end virtual staining framework, utilizing such contrasts. Virtually stained thin and fresh tissue exhibit high concordance when compared against histochemical staining. The proposed work paves the way for developing TA-PARS slide-free histology, which may revolutionize intraoperative microscopic diagnosis and margin assessment.

While photoacoustic imaging can reach depths of several centimeters in soft tissue, bone tissue is hard to penetrate. Which is why so far, transcranial photoacoustic imaging has proved challenging to implement - with the main challenge being acoustic losses in the skull. Our overall goal is to investigate the feasibility of transcranial photoacoustic sensing and imaging, and to study its usefulness for monitoring hemodynamics. In this study we focus on the acoustic constraints imposed by the skull and present the initial results from our ex vivo human skull phantoms.

High-intensity focused ultrasound (HIFU) capitalizes on both heating and cavitation effects for the treatment of several conditions. Optoacoustic (OA) imaging has previously been shown to provide high sensitivity to temperature changes and coagulation in HIFU-ablated tissues. In this work, we demonstrate the feasibility of real-time monitoring of heating and cavitation with a hybrid optoacoustic-ultrasound (OPUS) imaging system based on a multi-segment transducer array. The OPUS results in experiments with liver tissues ex-vivo and a mouse post-mortem were validated with thermal camera measurements and with cryo-sections of the mouse. The suggested approach thus holds promise to be clinically translated.

Kidney transplantation is the treatment of choice for most patients with end-stage kidney disease. Before transplantation, the kidney has to be carefully evaluated. In this study, we investigate the added value of photoacoustic imaging (PA) employed for kidney quality evaluation. Specifically, the oxygenation of the pig kidney was quantified and used as the quality metric. We quantified the oxygenation of perfused kidneys separated between control and experimental (with induced necrosis) groups. The preliminary results suggest that the oxygenation level can be a valuable metric of kidney quality.

A new ultrasound-detection technology is developed for ultrahigh-resolution optoacoustic tomography and is experimentally demonstrated with bandwidths exceeding 200 MHz and lateral resolutions beyond 20 µm. Our technology is based on an optical resonator fabricated in a silicon-photonics platform, which is coated by a sensitivity-enhancing polymer, which also eliminates the parasitic effect of surface acoustic waves. Further improvement in sensitivity is achieved by a low-noise interferometric setup, which eliminates the effect of laser frequency noise on the measurement. In vivo optoacoustic tomography is performed on a mouse ear, revealing its vasculature at detail that has been previously reserved to optoacoustic microscopy.

Deep tissue applications (>1 cm) for photoacoustic imaging are limited for traditional Fabry-Perot (FP) ultrasound transducers interrogated by tightly focused Gaussian beams due to beam walk-off, but are in principle feasible for plano-concave optical microresonator (PCMR) sensors. However, in practice, making PCMR sensors with sufficiently high sensitivity is challenging. We explore several approaches to maximise sensitivity and overcome the limitations associated with using high-Q PCMR sensors. The results show an improvement in the sensitivity and the minimum detectable pressure, enabling an increase of the penetration depth in tomographic photoacoustic imaging.

Planar Fabry-Pérot (FP) ultrasound sensor arrays are capable of high fidelity photoacoustic images. This is due to their ability to sample very densely with small element sizes which exhibit high sensitivity over a very wide bandwidth. However, their planar geometry results in limited-view image artefacts, as well as limiting the visualisation of deeper lying anatomical structures required in some preclinical studies. To address this limitation, a multi-view FP photoacoustic (PA) scanner was developed, enabling full-field detection, thereby overcoming the limited-view restriction while retaining the significant advantages of the FP sensor. This enabled the acquisition of 3-D whole-body PA images of a mouse anatomy with unprecedented quality.

We present a novel microscopy technique called photoacoustic remote sensing combined with autofluorescence with surface excitation (PARS-AMUSE) to generate virtual hematoxylin and eosin (H&E) images with simultaneous metabolic measurements to predict cancer aggression. PARS uses absorption and scattering contrast for the virtual H&E images to visualize structural information, perform margin assessment and grade cancers. AMUSE utilizes the same light source used in PARS to excite NADH and FAD autofluorescence for quantifying the optical redox ratio (ORR), an important indicator of tissue metabolism. Using our system, we aim to differentiate receptor status and predict cancer aggression.

Fabry-Perot tomographs have captured some of the most compelling photoacoustic images as they combine small element sizes with high acoustic sensitivity and a broad frequency response. A major fabrication challenge is the homogenization across large sensor areas. In this study, a spin coated photopolymer is used as spacer material. Its thickness can be modified spatially using UV light source leading to homogenization over areas of 2 x 2 cm2. The optical transfer function, acoustic sensitivity, and frequency response were measured using a camera-based tomograph. The imaging capabilities were demonstrated by capturing acoustic fields emitted by a transducer and PA phantoms.

Fabry-Perot scanners are typically read-out in a sequential manner. An alternative approach is to use a widefield illumination and measure the reflected light in parallel using a camera. This approach allows for a finer spatial sampling of the Fabry-Perot sensor and can speed up the image acquisition. In a first instance, the capability of the camera-based approach to finely spatially sample the sensor, with the means of improving image resolution, was demonstrated. In a second instance, the ability of the camera-based system to acquire 3D photoacoustic images in 200 ms when operating at a PRF of 1 kHz was demonstrated.

Histological analysis of tissues is the current gold standard utilized by pathologists in reviewing excised tumor specimen margins. However, as a result of time-consuming and labor-intensive pre-processing steps this approach leads to postponed post-operative feedback to surgeons resulting in worsened patient prognosis. In this work we introduce a combined ultraviolet confocal reflectance and photoacoustic remote sensing microscopy system that allows tightly optically sectioned high-resolution virtual histology imaging of freshly excised thick tissues label-free. By removing tissue preparation steps, this technique has real potential to translate post-operative feedback into the surgical suite.

We demonstrate a rapid photoacoustic remote sensing (PARS) microscopy system with voice-coil stage scanning, capable of acquiring 1cm2 virtual histology images at 800nm x 800nm lateral sampling density in 3.75 minutes, high-resolution (300nm x 300nm sampling density) images at 1mm2 in 20 seconds and 300μm x 300μm in 3 seconds. The combined resolution and scanning speed that can be achieved by this system may pave way for clinical translation to rapidly assess resected tumor margins in the surgical suite.

An automated label-free virtual histology microscope using Photoacoustic Remote Sensing (PARS) microscopy is presented. This device features an optimized architecture providing additional contrasts, and enhancements in image quality and SNR over previous PARS virtual histology embodiments. Concurrently, developments in software and signal processing enable automated scanning of tissue specimens within minutes. Finally, AI-based virtual staining facilitates visualizations analogous to current histochemical staining. The diagnostic utility is demonstrated in unprocessed human tissues. Results validated through clinical efficacy studies demonstrate comparable contrast and diagnostic quality to gold standard histological preparations. This represents a significant step towards a clinical system for virtual pathology.

Purposed at validating the hypothesis that overly stiff sclera undermines the passive and adaptive mechanisms of the aqueous outflow pathway in regulating IOP, we combined photoacoustic microscopy (PAM) and finite element analysis (FEA) technologies to resolve and quantify the strains in the aqueous veins and surrounding perilimbal sclera in human and porcine eyes at high resolution in 3D in our previous study. In this study, we introduced large dynamic range of scleral stiffness in intact porcine eyes by crosslinking and observed the correlations between the principal strains in sclera and aqueous veins during IOP elevations, and between the principal strains and the steady state IOP. The results showed strong correlations in both cases.

Photoacoustic imaging (PAI) has highly desirable features but has struggled with clinical translation. Photothermal therapy (PTT) is a new minimally invasive treatment that facilitates thermal tumor destruction using NIR lasers and thin optical fibers placed into the tumor. Here we show that bulk tissue temperature imaging for PTT guidance is achievable at centimeters of depth when a task-specific instrument is designed and built. Furthermore, we highlight a PTT guidance platform prototype including PAI thermometry and MRI-compatible diffuse optical treatment response probe, which when combined with tumor localizing nanoparticles (Porphysomes) provide the 3 main features required for clinical translation of PTT, i.e., tumor localization, tissue temperature, and treatment response. Visualization of pure temperature contrast in tissue mimicking coagulating phantoms and ex-vivo tissues is shown, as well as clinical in-patient optical monitoring of PTT for prostate cancer.

Focusing light into an arbitrary pattern through multimode fiber is highly desired in energy delivery-related biomedical applications and has been demonstrated feasible with wavefront shaping. Here, the strategy relying on natural gradient ascent-based parameter optimization is shown to search the optimal wavefront rapidly towards high-quality pattern projection through a multimode fiber. Meanwhile, a new fitness function based on cosine similarity is adopted to replace the commonly used Pearson correlation coefficient, which leads to higher pattern contrast without sacrificing the fidelity with the target. With the proposed scheme, long-distance projection of arbitrary pattern was demonstrated through a 15-meter unfixed multimode fiber, showing fast convergence and better anti-interference ability. The superior performance of our approach for generating arbitrary pattern may gains special interest in multimode fiber based deep-tissue photon therapy and optogenetics.

In this study, a computationally efficient integration of delay-multiply-and-sum (DMAS) photoacoustic (PA) image reconstruction and minimum-variance beamformation (MV), named as MV-HDMAS, is developed to drastically improve the lateral resolution and suppress sidelobes; thus significantly improving the contrast. Here, a novel Hilbert transform based DMAS (H-DMAS) is adopted, which allows seamless integration with MV. MV here is used to optimize the aperture apodization for H-DMAS. No oversampling and band pass filtering as in radio frequency DMAS are required. Experimental results confirm not only the superior lateral resolution in the proposed MV-HDMAS but also comparable image contrast to DMAS counterpart.

We previously demonstrated that temporarily induced bubbles in ultrasound energy can be used to increase the penetration of light into biological tissue by acting as an optical scattering agent in the biological tissue. In this paper, we study the effect of light fluence on the bubble concentration in the bubble cloud region using monte carlo simulation and tissue mimicking phantom. As a result, we found that optical scattering increased and the fluctuation in the light intensity became stronger as the bubble concentration decrease.

High-frequency photoacoustic (PA) imaging (<20 MHz) requires data acquisition (DAQ) with commensurately high sampling rate, which leads to hardware challenges and increased costs. We report a new method—interleave-sampled PA imaging that enables high-frequency imaging with a relatively low sampling rate, e.g., a 30-MHz transducer with 40-MHz sampling rate. This method harnesses two acquisitions at a low sampling rate to effectively double the sampling rate. It modulates the delay of the light pulses and can thus be applied to any PA DAQ system.

Photoacoustic tomography has great potential; however, limited detector coverage is a key issue that results in artifacts. While analytical and simulation studies regarding this issue are extensive, experimental setups are lacking. A ring-shaped detector array was rotated and translated to achieve near-full view angle coverage. Following system optimization, phantom imaging of star shape, synthetic breast tumor specimen, and vascular phantoms was performed. Approximately 4000 detectors were needed for high quality images, and phantoms were clearly imaged with minimal artifacts. A near full-view spherical system has been developed, allowing for future work validating experimentally the theoretical advantages of using a full-view setup.

The spatial resolution limit in photoacoustic/thermal imaging is derived from the irreversibility of attenuation of the pressure wave and of heat diffusion during propagation of the signals from the imaged subsurface structures to the sample surface, respectively. The acoustic or temperature signals are converted into so-called virtual waves, which are their reversible counterparts, and which can be used for image reconstruction by well-known ultrasound reconstruction methods, which is an ill-posed inverse problem. The resolution from entropy production is equal to the diffraction limit -which is noise limited. Incorporating sparsity and non-negativity in iterative regularization methods gives a significant resolution enhancement.

We present the development of a multimodal photoacoustic and ultrasound imaging arrangement to investigate various conditioned pig livers during ex-vivo machine perfusion. Light and acoustic wave propagation simulation were performed with realistic optical and acoustical organ properties. Based on the simulation results, an optimized photoacoustic excitation and detection schemes were developed. Since the temperature of used perfusion liquids can be controlled, also temperature inhomogeneities were considered in the simulation. Preliminary experiments were performed with two single element detectors and a 2D-PA/US linear array probe.

Blood supply in bone plays a crucial role in bone growth and fracture healing. However, to accurately reconstruct photoacoustic images of blood in bone, we must consider the refraction experienced by acoustic waves when passing through bone. We utilise ultrasound to determine the heterogeneous wave speed model which is then used for refraction-corrected photoacoustic imaging. We further extend new photoacoustic velocimetry techniques by accounting for refraction to generate maps showing the location, speed and direction of flowing optical absorbers in bone models. This technique is validated on in vitro experimental data obtained from a blood-vessel phantom beneath a bone-mimicking plate.

In photoacoustic images with mechanical scanning of single-element ultrasound transducers, respiratory movements generate distortion in data due to slow imaging speed. To overcome this technical issue, we propose an ultrasound-guided breath-compensation method for volumetric photoacoustic data. We have successfully corrected the breath-related distortion by using simultaneously acquired ultrasound data. The resulting three-dimensional photoacoustic images can visualize volumetric hemoglobin oxygen saturation map in the whole body of mice. We believe that these results can provide a more accurate analytical perspective for biomedical imaging studies.

Photoacoustic imaging technology using multi-wavelength can achieve functional image that provide information about a singularity in an image target. We developed a wavelength tunable light source pumped by few tens kHz pulsed laser with 532 nm wavelength for single scan functional photoacoustic imaging. The laser has individual output pulses with about 200 nsec time delay between the original 532 nm pump pulse and the wavelength tunable pulse. By using the ping-pong pulse output, we have make enable to obtain a functional photoacoustic image in a single laser scanning and demonstrated functional photoacoustic microscopy imaging to show a mouse activity.

Ultrasound (US) imaging is commonly used to guide minimally invasive surgeries but has poor contrast of the invasive devices such as clinical needles. Photoacoustic (PA) imaging promises to be efficient for visualising needles. Elastomeric coatings can also be applied on the needle surface to improve its visibility, however, strong signals generated from the highly absorbing coatings sometimes introduce image artefacts which affect needle identification. In this work, we developed a deep learning-based method to enhance the needle visualisation by removing the artefacts. We anticipated that the proposed methods could be useful for guiding percutaneous needle insertions.

Photoacoustic (PA) imaging has demonstrated tremendous potential for various clinical and pre-clinical applications in the past two decades. Laser diodes and light-emitting diodes can be used as substitutes for solid-state lasers with the benefits of low cost and compact size. However, PA signals generated by such light sources have relatively low signal-to-noise ratios due to the low output energy. Here, we proposed a spatiotemporal singular value decomposition denoising method for PA radiofrequency data acquired at high frame rates. Within silico and in vivo experiments, it outperformed frame averaging and could be used for real-time in vivo applications.

The long-term objective of the program is to develop a highly innovative platform to measure the health of human calcaneus in vivo by using our recently invented photoacoustic techniques. To better calibrate the platform and investigate the bone properties, a phantom which simulates the optical, ultrasound and architectural properties of human calcaneus is required. In this work, a semi-anthropomorphic photoacoustic calcaneus phantom is developed based on micro-CT and SLA 3D printing techniques. The measured microarchitectural, optical and ultrasound properties of the phantom are all consistent with those in human calcaneus in vivo.

Translation of photoacoustic (PA) imaging for abdominal imaging requires an optimized optical illumination for deep tissue light delivery. Simulations-based optimization of laser beam size has not been tested for deep imaging depths (< 0.5 cm). Additionally, while conventional PA imaging uses wavelengths in the first near infrared (NIR) window, tissue attenuation is minimized in the NIR-2 window, allowing for greater fluence penetration. In this study, Monte-Carlo simulated fluence maps were validated using PA images acquired of a lead-polystyrene phantom with lead positioned at multiple depths (1-4 cm) and illuminated with a 750 nm beam of varying widths (0.8-2.0 cm). At imaging depths of 4 cm, a 2× increase in fluence deposition when increasing beam diameter by a factor of 1.5, was consistently observed between MC simulations and experimental imaging. Using an optimized 1064 nm beam with a 1.6 cm beam, an 8× increase in deposited fluence at similar depths is observed.

Peripheral artery disease (PAD) is widespread among the elderly population where narrowing arteries in lower limbs are causing a lack of perfusion. This work explores the benefit of volumetric photoacoustic imaging (v-PAI) over conventional 2D PAI for PAD diagnosis and monitoring. To this end, we leverage the recently proposed approach of Tattoo tomography, which generates a v-PAI representation from a set of 2D PAI slices. Preliminary results of the ongoing study indicate that v-PAI can increase the sensitivity of early-stage PAD detection. Conclusively our Tattoo approach has the potential to become a valuable tool in PAD diagnostics.

Optical and acoustic imaging techniques enable noninvasive visualization of structural and functional tissue properties. Data-driven approaches for quantification of these properties are promising, but they rely on highly accurate simulations due to the lack of ground truth knowledge. We recently introduced the open-source simulation and image processing for photonics and acoustics (SIMPA) Python toolkit that has quickly been adopted by the community in the context of the IPASC consortium for standardized reconstruction. We present new developments in the toolkit including e.g. improved tissue and device modeling and provide an outlook on future directions aiming at improving the realism of simulations.

While laser can acquire ultra-high-resolution image at desired area, the penetration depth of light is limited due to tissue scattering, making it difficult to reach deep depths. For this, we previously proposed a technique that uses ultrasonic energy to temporarily generate bubbles in the ultrasonic path to suppress scattering and increase the penetration depth. However, it is hard to accurately create bubbles in a preferred position due to randomly generated within the depth of focus. In this study, we introduce a Laser-induced bubble generation technique combined with ultrasound that can make bubbles at precise locations while maintaining high light transmittance.

Neoadjuvant chemotherapy (NAC) is a systemic therapy used to treat breast cancer prior to surgery. Multispectral photoacoustic (PA) imaging has been showing promising results in breast cancer. However, in order to use PA imaging in NAC response monitoring registration of the serial PA images is needed. In this study we propose and validate an automatic image registration algorithm to align intra-patient repeated breast PA images that can correct for patient repositioning and local non-rigid tissue deformation. Thanks to this algorithm, PA imaging can prove to be a non-invasive technique capable of monitoring the tumour functionality over time.

High-quality photoacoustic compatible phantoms can facilitate the imaging standardization and clinical translation of this emerging technique. We optimized the receipt of a copolymer-in-oil material, which has been recently proposed as a candidate photoacoustic-compatible material. Moreover, we proposed the methodology to fabricate a realistic, durable, and photoacoustic-compatible phantom by combining image-based modeling and 3D-printing techniques for clinical application. Beyond the fabrication, a detailed optical and acoustic characterization is also provided. The proposed tissue-mimicking phantom offers a tradeoff between manufacturing abilities, durability, reproducibility, and compatibility of the material. Furthermore, the phantom is durable and stable over time under storage and repeated use.

In photoacoustic tomography, the target object is illuminated by a short-pulsed light and multiple ultrasonic transducers are used to measure PA waves. Image reconstruction is needed to create a map of the initial acoustic pressure. In case of insufficient number of projections (views) around the object, the reconstructed image suffers from lower quality. We trained a CNN to improve the quality of less-view breast PA images, using the full-view reconstructions as ground-truth. The proposed network can reduce the acquisition time while preserving image quality.