多谱线光声断层摄影术的癌症异质性光学成像

目的考察多谱线光声断层摄影术(MSOT)在展示目标外源物质的不均匀分布状况和活体样本恶性肿瘤中直径在毫米级的血管的特征等方面的能力。材料与方法实验中涉及的对动物的操作经上巴伐利亚行政区政府批准。研究人员使用一台MSOT装置(产生横断面图像速度为10帧/s,平面内分辨率约为150μm)对小鼠皮下肿瘤进行成像。为了研究动态对比强化,研究人员系统性地对3只患4T1型肿瘤的小鼠进行注射吲哚菁绿(ICG)操作,并在该操作前、注射时及注射后20 min,4 h和24 h对上述小鼠进行成像。荧光显微镜成像结果被用于对比。靶向荧光剂(注射6 h后)和血红蛋白氧合物的MSOT同时进行(4T1型肿瘤:n=3)。冰冻切片的荧光显微镜成像结果被用于验证上述结果。研究人员利用长循环时间金纳米棒对由于渗透性增加和肿瘤(4T1型肿瘤:n=4,HT29型肿瘤:n=3,A2780型肿瘤:n=2)内的滞留产生的积聚效应进行评估(注射前,注射时,注射后1 h,5 h和24 h)。暗场显微镜检查结果被用于验证上述结果。结果吲哚菁绿可用于动态对比强化。与荧光显微镜成像对比,MSOT显示了肿瘤内药剂的不均匀分布。靶向荧光剂和脱氧血红蛋白的同时成像让研究人员除目标药物摄取程度外,还可以了解肿瘤内的血管系统。久而久之在MSOT影像中看到的肿瘤中的金纳米棒的积聚过程,也呈异质性吸收。结论 MSOT技术可用于肿瘤的即时高空间分辨率观测,用以展示目标荧光染料、纳米材料以及肿瘤内部血管网的影像资料。

Highly sensitive miniature needle PVDF-TrFE ultrasound sensor for optoacoustic microscopy

A wideband sensitive needle ultrasound sensor based on a polarized PVDF-TrFE copolymer piezoelectric film has been developed,which is capable of providing a noise equivalent pressure of 14 Pa and a uniform frequency response ranging from 1 to 25 MHz.Its high sensitivity(1.6μV∕Pa)and compact size were achieved by capitalizing on the large electromechanical coupling coefficient of PVDF-TrFE and minimizing parasitic capacitance in a two-stage amplifier structure.The detection sensitivity of the newly designed sensor outperformed commercially available hydrophones with an equivalent sensing element area by a factor of 9.The sensor has been successfully integrated into a light scanning optoacoustic microscopy(OAM)system with a limited working space.Submicrometer resolution images were subsequently attained from living mice without employing signal averaging.The miniature sensor design can readily be integrated into various OAM systems and further facilitate multimodal imaging system implementations.

Functional optoacoustic neuro-tomography for scalable whole-brain monitoring of calcium indicators

Non-invasive observation of spatiotemporal activity of large neural populations distributed over entire brains is a longstanding goal of neuroscience.We developed a volumetric multispectral optoacoustic tomography platform for imaging neural activation deep in scattering brains.It can record 100 volumetric frames per second across scalable fields of view ranging between 50 and 1000 mm^(3) with respective spatial resolution of 35–200μm.Experiments performed in immobilized and freely swimming larvae and in adult zebrafish brains expressing the genetically encoded calcium indicator GCaMP5G demonstrate,for the first time,the fundamental ability to directly track neural dynamics using optoacoustics while overcoming the longstanding penetration barrier of optical imaging in scattering brains.The newly developed platform thus offers unprecedented capabilities for functional whole-brain observations of fast calcium dynamics;in combination with optoacoustics'well-established capacity for resolving vascular hemodynamics,it could open new vistas in the study of neural activity and neurovascular coupling in health and disease.

Transmission-reflection optoacoustic ultrasound(TROPUS)computed tomography of small animals

Rapid progress in the development of multispectral optoacoustic tomography techniques has enabled unprecedented insights into biological dynamics and molecular processes in vivo and noninvasively at penetration and spatiotemporal scales not covered by modern optical microscopy methods.Ultrasound imaging provides highly complementary information on elastic and functional tissue properties and further aids in enhancing optoacoustic image quality.We devised the first hybrid transmission–reflection optoacoustic ultrasound(TROPUS)small animal imaging platform that combines optoacoustic tomography with both reflection-and transmission-mode ultrasound computed tomography.The system features full-view cross-sectional tomographic imaging geometry for concomitant noninvasive mapping of the absorbed optical energy,acoustic reflectivity,speed of sound,and acoustic attenuation in whole live mice with submillimeter resolution and unrivaled image quality.Graphics-processing unit(GPU)-based algorithms employing spatial compounding and bent-ray-tracing iterative reconstruction were further developed to attain real-time rendering of ultrasound tomography images in the full-ring acquisition geometry.In vivo mouse imaging experiments revealed fine details on the organ parenchyma,vascularization,tissue reflectivity,density,and stiffness.We further used the speed of sound maps retrieved by the transmission ultrasound tomography to improve optoacoustic reconstructions via two-compartment modeling.The newly developed synergistic multimodal combination offers unmatched capabilities for imaging multiple tissue properties and biomarkers with high resolution,penetration,and contrast.

Adding fifth dimension to optoacoustic imaging: volumetric time-resolved spectrally enriched tomography

Optoacoustics provides a unique set of capabilities for bioimaging,associated with the intrinsic combination of ultrasound-and light-related advantages,such as high spatial and temporal resolution as well as powerful spectrally enriched imaging contrast in biological tissues.We demonstrate here,for the first time,the acquisition,processing and visualization of five-dimensional optoacoustic data,thus offering unparallel imaging capacities among the current bioimaging modalities.The newly discovered performance is enabled by simultaneous volumetric detection and processing of multispectral data and is further showcased here by attaining time-resolved volumetric blood oxygenation maps in deep human vessels and real-time tracking of contrast agent distribution in a murine model in vivo.

Localization optoacoustic tomography

Localization-based imaging has revolutionized fluorescence optical microscopy and has also enabled unprecedented ultrasound images of microvascular structures in deep tissues.Herein,we introduce a new concept of localization optoacoustic tomography(LOT)that employs rapid sequential acquisition of three-dimensional optoacoustic images from flowing absorbing particles.We show that the new method enables breaking through the spatial resolution barrier of acoustic diffraction while further enhancing the visibility of structures under limited-view tomographic conditions.Given the intrinsic sensitivity of optoacoustics to multiple hemodynamic and oxygenation parameters,LOT may enable a new level of performance in studying functional and anatomical alterations of microcirculation.

Multifocal structured illumination optoacoustic microscopy

Optoacoustic(OA)imaging has the capacity to effectively bridge the gap between macroscopic and microscopic realms in biological imaging.High-resolution OA microscopy has so far been performed via point-by-point scanning with a focused laser beam,thus greatly restricting the achievable imaging speed and/or field of view.Herein we introduce multifocal structured illumination OA microscopy(MSIOAM)that attains real-time 3D imaging speeds.For this purpose,the excitation laser beam is shaped to a grid of focused spots at the tissue surface by means of a beamsplitting diffraction grating and a condenser and is then scanned with an acousto-optic deflector operating at kHz rates.In both phantom and in vivo mouse experiments,a 10mm wide volumetric field of view was imaged with 15 Hz frame rate at 28μm spatial resolution.The proposed method is expected to greatly aid in biological investigations of dynamic functional,kinetic,and metabolic processes across multiple scales.

Non-invasive determination of murine placental and foetal functional parameters with multispectral optoacoustic tomography

Despite the importance of placental function in embryonic development,it remains poorly understood and challenging to characterize,primarily due to the lack of non-invasive imaging tools capable of monitoring placental and foetal oxygenation and perfusion parameters during pregnancy.We developed an optoacoustic tomography approach for real-time imaging through entire ~4 cm cross-sections of pregnant mice.Functional changes in both maternal and embryo regions were studied at different gestation days when subjected to an oxygen breathing challenge and perfusion with indocyanine green.Structural phenotyping of the cross-sectional scans highlighted different internal organs,whereas multi-wavelength acquisitions enabled non-invasive label-free spectroscopic assessment of blood-oxygenation parameters in foeto-placental regions,rendering a strong correlation with the amount of oxygen administered.Likewise,the placental function in protecting the embryo from extrinsically administered agents was substantiated.The proposed methodology may potentially further serve as a probing mechanism to appraise embryo development during pregnancy in the clinical setting.

Single-sweep volumetric optoacoustictomography of whole mice

Applicability of optoacoustic imaging in biology and medicine is determined by several key performance characteristics.In particular,an inherent trade-off exists between the acquired field-of-view(FOV)and temporal resolution of the measurements,which may hinder studies looking at rapid biodynamics at the whole-body level.Here,we report on a single-sweep volumetric optoacoustic tomography(sSVOT)system that attains whole body three-dimensional mouse scans within 1.8 s with better than 200μm spatial resolution.sSVOT employs a spherical matrix array transducer in combination with multibeam illumination,the latter playing a critical role in maximizing the effective FOV and imaging speed performance.The system further takes advantage of the spatial response of the individual ultrasound detection elements to mitigate common image artifacts related to limited-view tomographic geometry,thus enabling rapid acquisitions without compromising image quality and contrast.We compare performance metrics to the previously reported whole-body mouse imaging implementations and alternative image compounding and reconstruction strategies.It is anticipated that sSVOT will open new venues for studying large-scale biodynamics,such as accumulation and clearance of molecular agents and drugs across multiple organs,circulation of cells,and functional responses to stimuli.

Accounting for speed of sound variations in volumetric hand-held optoacoustic imaging

Hand-held implementations of recently intro- duced real-time volumetric tomography approaches repre- sent a promising path toward clinical translation of the optoacoustic technology. To this end, rapid acquisition of optoacoustic image data with spherical matrix arrays has attained exquisite visualizations of three-dimensional vascular morphology and function deep in human tissues. Nevertheless, significant reconstruction inaccuracies may arise from speed of sound （SOS） mismatches between the imaged tissue and the coupling medium used to propagate the generated optoacoustic responses toward the ultra- sound sensing elements. Herein, we analyze the effects of SoS variations in three-dimensional hand-held tomo- graphic acquisition geometries. An efficient graphics processing unit （GPU）-based reconstruction framework is further proposed to mitigate the SoS-related image quality degradation without compromising the high-frame-rate volumetric imaging performance of the method, essential for real-time visualization during hand-held scans.

Spiral volumetric optoacoustic tomography visualizes multi-scale dynamics in mice

Imaging dynamics at different temporal and spatial scales is essential for understanding the biological complexity of living organisms,disease state and progression.Optoacoustic imaging has been shown to offer exclusive applicability across multiple scales with excellent optical contrast and high resolution in deep-tissue observations.Yet,efficient visualization of multi-scale dynamics remained difficult with state-of-the-art systems due to inefficient trade-offs between image acquisition time and effective field of view.Herein,we introduce the spiral volumetric optoacoustic tomography technique that provides spectrally enriched highresolution contrast across multiple spatiotemporal scales.In vivo experiments in mice demonstrate a wide range of dynamic imaging capabilities,from three-dimensional high-frame-rate visualization of moving organs and contrast agent kinetics in selected areas to whole-body longitudinal studies with unprecedented image quality.The newly introduced paradigm shift in imaging of multi-scale dynamics adds to the multifarious advantages provided by the optoacoustic technology for structural,functional and molecular imaging.

Hybrid magnetic resonance and optoacoustic tomography(MROT) for preclinical neuroimaging

Multi-modal imaging is essential for advancing our understanding of brain function and unraveling pathophysiological processes underlying neurological and psychiatric disorders.Magnetic resonance(MR)and optoacoustic(OA)imaging have been shown to provide highly complementary contrasts and capabilities for preclinical neuroimaging.True integration between these modalities can thus offer unprecedented capabilities for studying the rodent brain in action.We report on a hybrid magnetic resonance and optoacoustic tomography(MROT)system for concurrent noninvasive structural and functional imaging of the mouse brain.Volumetric OA tomography was designed as an insert into a high-field MR scanner by integrating a customized MR-compatible spherical transducer array,an illumination module,and a dedicated radiofrequency coil.A tailored data processing pipeline has been developed to mitigate signal crosstalk and accurately register image volumes acquired with T1-weighted,angiography,and blood oxygenation level-dependent(BOLD)sequences onto the corresponding vascular and oxygenation data recorded with the OA modality.We demonstrate the concurrent acquisition of dual-mode anatomical and angiographic brain images with the scanner,as well as real-time functional readings of multiple hemodynamic parameters from animals subjected to oxygenation stress.Our approach combines the functional and molecular imaging advantages of OA with the superb soft-tissue contrast of MR,further providing an excellent platform for cross-validation of functional readings by the two modalities.