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.

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.

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.

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.

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.