Vascular remodeling of the mouse embryonic yolk sac is a highly dynamic process dependent on multiple genetic signaling pathways as well as biomechanical factors regulating proliferation, differentiation, migration, cell-cell, and cell-matrix interactions. During this early developmental window, the initial primitive vascular network of the yolk sac undergoes a dynamic remodeling process concurrent with the onset of blood flow, in which endothelial cells establish a branched, hierarchical structure of large vessels and smaller capillary beds. In this review, we will describe the molecular and biomechanical regulators which guide vascular remodeling in the mouse embryonic yolk sac, as well as live imaging methods for characterizing endothelial cell and hemodynamic function in cultured embryos.
We report on a quantitative optical elastographic method based on shear wave imaging optical coherence tomography (SWI-OCT) for biomechanical characterization of cardiac muscle through noncontact elasticity measurement. The SWI-OCT system employs a focused air-puff device for localized loading of the cardiac muscle and utilizes phase-sensitive OCT to monitor the induced tissue deformation. Phase information from the optical interferometry is used to reconstruct 2-D depth-resolved shear wave propagation inside the muscle tissue. Cross-correlation of the displacement profiles at various spatial locations in the propagation direction is applied to measure the group velocity of the shear waves, based on which the Young's modulus of tissue is quantified. The quantitative feature and measurement accuracy of this method is demonstrated from the experiments on tissue-mimicking phantoms with the verification using uniaxial compression test. The experiments are performed on ex vivo cardiac muscle tissue from mice with normal and genetically altered myocardium. Our results indicate this optical elastographic technique is useful as a noncontact tool to assist the cardiac muscle studies.
The main hypothesis suggested that changes in the external mechanical load would lead to different deformations of the submembranous cytoskeleton and, as a result, dissociation of different proteins from its structure (induced by increased/decreased mechanical stress). The study subjects were fibers of the soleus muscle and cardiomyocytes of Wistar rats. Changes in external mechanical conditions were reconstructed by means of antiorthostatic suspension of the animals by their tails for 6, 12, 18, 24 and 72 hours. Transversal stiffness was measured by atomic force microscopy imaging; beta-, gamma-actin, alpha-actinin 1 and alpha-actinin 4 levels in membranous and cytoplasmic fractions were quantified by Western blot analysis; expression rates of the corresponding genes were studied using RT-PCR.
The recent evolution of genomics and subsequently proteomics offers a major advance in the ability to understand individual human variation in disease and the molecular level changes induced by certain environmental exposures. This original study examines urinary proteome composition to enable the understanding of molecular homeostatic mechanisms in spaceflight and presents the potential for early detection of subclinical disease, microgravity risk mitigation strategies, and countermeasure development for exploration-class missions.
Multimodal imaging offers the potential to improve diagnosis and enhance the specificity of photothermal cancer therapy. Toward this goal, gadolinium-conjugated gold nanoshells are engineered and it is demonstrated that they enhance contrast for magnetic resonance imaging, X-ray, optical coherence tomography, reflectance confocal microscopy, and two-photon luminescence. Additionally, these particles effectively convert near-infrared light to heat, which can be used to ablate cancer cells. Ultimately, these studies demonstrate the potential of gadolinium-nanoshells for image-guided photothermal ablation.
The urine protein composition samples of ten Russian cosmonauts (male, aged of 35 up to 51) performed long flight missions and varied from 169 up to 199 days on the International Space Station (ISS) were analyzed. As a control group, urine samples of six back-up cosmonauts were analyzed. We used proteomic techniques to obtain data and contemporary bioinformatics approaches to perform the analysis. From the total number of identified proteins (238) in our data set, 129 were associated with a known tissue origin. Preflight samples contained 92 tissue-specific proteins, samples obtained on Day 1 after landing had 90 such proteins, while Day 7 samples offered 95 tissue-specific proteins. Analysis showed that consistently present proteins in urine (under physiological conditions and after space flight) are cubilin, epidermal growth factor, kallikrein-1, kininogen-1, megalin, osteopontin, vitamin K-dependent protein Z, uromodulin. Variably present proteins consists of: Na(+)/K(+) ATPase subunit gamma, ?-defensin-1, dipeptidyl peptidase 4, maltasa-glucoamilasa, cadherin-like protein, neutral endopeptidase and vascular cell adhesion protein 1. And only three renal proteins were related to the space flight factors. They were not found in the pre-flight samples and in the back-up cosmonaut urine, but were found in the urine samples after space flight: AFAM (afamin), AMPE (aminopeptidase A) and AQP2 (aquaporin-2). This data related with physiological readaptation of water-salt balance. The proteomic analysis of urine samples in different phases of space missions with bioinformation approach to protein identification provides new data relative to biomechemical mechanism of kidney functioning after space flight.
The extracellular matrix of epithelial tumors undergoes structural remodeling during periods of uncontrolled growth, creating regional heterogeneity and torsional stress. How matrix integrity is maintained in the face of dynamic biophysical forces is largely undefined. Here we investigated the role of fibulin-2, a matrix glycoprotein that functions biomechanically as an inter-molecular clasp and thereby facilitates supra-molecular assembly. Fibulin-2 was abundant in the extracellular matrix of human lung adenocarcinomas and was highly expressed in tumor cell lines derived from mice that develop metastatic lung adenocarcinoma from co-expression of mutant K-ras and p53. Loss-of-function experiments in tumor cells revealed that fibulin-2 was required for tumor cells to grow and metastasize in syngeneic mice, a surprising finding given that other intra-tumoral cell types are known to secrete fibulin-2. However, tumor cells grew and metastasized equally well in Fbln2-null and -wild-type littermates, implying that malignant progression was dependent specifically upon tumor cell-derived fibulin-2, which could not be offset by other cellular sources of fibulin-2. Fibulin-2 deficiency impaired the ability of tumor cells to migrate and invade in Boyden chambers, to create a stiff extracellular matrix in mice, to cross-link secreted collagen, and to adhere to collagen. We conclude that fibulin-2 is a driver of malignant progression in lung adenocarcinoma and plays an unexpected role in collagen cross-linking and tumor cell adherence to collagen.
Understanding the nature and mechanism of congenital defects of the different organ systems in humans has heavily relied on the analysis of the corresponding mutant phenotypes in rodent models. Optical Coherence Tomography (OCT) has recently emerged as a powerful tool to study early embryonic development. This non-invasive optical methodology does not require labeling and allows visualization of embryonic tissues with single cell resolution. Here, we will discuss how OCT can be applied for structural imaging of early mouse and rat embryos in static culture, cardiodynamic and blood flow analysis, and in utero embryonic imaging at later stages of gestation, demonstrating how OCT can be used to assess structural and functional birth defects in mammalian models.
Optical coherence tomography (OCT) allows imaging dynamic structures and fluid flow within scattering tissue, such as the beating heart and blood flow in murine embryos. For any given system, the frame rate, spatial resolution, field-of-view (FOV), and signal-to-noise ratio (SNR) are interconnected: favoring one aspect limits at least one of the others due to optical, instrumentation, and software constraints. Here we describe a spatio-temporal mosaicing technique to reconstruct high-speed, high spatial-resolution, and large-field-of-view OCT sequences. The technique is applicable to imaging any cyclically moving structure and operates on multiple, spatially overlapping tiled image sequences (each sequence acquired sequentially at a given spatial location) and effectively decouples the (rigid) spatial alignment and (non-rigid) temporal registration problems. Using this approach we reconstructed full-frame OCT sequences of the beating embryonic rat heart (11.5 days post coitus) and compared it to direct imaging on the same system, demonstrating a six-fold improvement of the frame rate without compromising spatial resolution, FOV, or SNR.
Although the mouse is a superior model to study mammalian embryonic development, high-resolution live dynamic visualization of mouse embryos remain a technical challenge. We present optical coherence tomography as a novel methodology for live imaging of mouse embryos through the uterine wall thereby allowing for time lapse analysis of developmental processes and direct phenotypic analysis of developing embryos. We assessed the capability of the proposed methodology to visualize structures of the living embryo from embryonic stages 12.5 to 18.5 days postcoitus. Repetitive in utero embryonic imaging is demonstrated. Our work opens the door for a wide range of live, in utero embryonic studies to screen for mutations and understand the effects of pharmacological and toxicological agents leading to birth defects.
Immersion is a useful tool for studying fluid-volume homeostasis. Natriuretic peptides play a vital role in renal, humoral, and cardiovascular regulation under changing environmental conditions. We hypothesized that dry immersion would rapidly induce a new steady state for water and sodium metabolism, and that serum NT-proBNP levels, a proxy measure for brain natriuretic peptide (BNP), would decrease during long-term dry immersion and increase during recovery. Eight healthy young men were studied before, during, and after 7 days of dry immersion. Body weight, water balance, and plasma volume changes were evaluated. Plasma and serum samples were analyzed for active renin, NT-proBNP, aldosterone, electrolytes, osmolality, total protein, and creatinine. Urine samples were analyzed to determine levels of electrolytes, osmolality, creatinine, and free cortisol. A stand test was performed before and after dry immersion to evaluate cardiovascular deconditioning. Long-term dry immersion induced acute changes in water and sodium homeostasis on day 1, followed by a new steady state. Plasma volume decreased significantly during dry immersion. The serum levels of NT-proBNP increased significantly in recovery (10 ± 3 ng/L before dry immersion vs. 26 ± 5 ng/L on the fourth recovery day). Heart rate in the standing position was significantly greater after immersion. Results suggest that chronic dry immersion rapidly induced a new level of water-electrolyte homeostasis. The increase in NT-proBNP levels during the recovery period may be related to greater cardiac work and might reflect the degree of cardiovascular deconditioning.
Dry immersion, which is a ground-based model of prolonged conditions of microgravity, is widely used in Russia but is less well known elsewhere. Dry immersion involves immersing the subject in thermoneutral water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. For a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. Unlike bed rest, dry immersion provides a unique opportunity to study the physiological effects of the lack of a supporting structure for the body (a phenomenon we call supportlessness). In this review, we attempt to provide a detailed description of dry immersion. The main sections of the paper discuss the changes induced by long-term dry immersion in the neuromuscular and sensorimotor systems, fluid-electrolyte regulation, the cardiovascular system, metabolism, blood and immunity, respiration, and thermoregulation. The long-term effects of dry immersion are compared with those of bed rest and actual space flight. The actual and potential uses of dry immersion are discussed in the context of fundamental studies and applications for medical support during space flight and terrestrial health care.
Actual and simulated microgravity induces hypovolemia and cardiovascular deconditioning, associated with vascular dysfunction. We hypothesized that vasoconstriction of skin microcirculatory bed should be altered following 7 days of simulated microgravity in order to maintain cardiovascular homeostasis during active standing. Eight healthy men were studied before and after 7 days of simulated microgravity modeled by dry immersion (DI). Changes of plasma volume and orthostatic tolerance were evaluated. Calf skin blood flow (laser-Doppler flowmetry), ECG and blood pressure signal during a 10-min stand test were recorded, and skin vascular resistance, central hemodynamics, baroreflex sensitivity and heart rate variability were estimated. After DI we observed increased calf skin vascular resistance in the standing position (12.0 ± 1.0 AU-after- vs. 6.8 ± 1.4 AU-before), while supine it was unchanged. Cardiovascular deconditioning was confirmed by greater tachycardia on standing and by hypovolemia (-16 ± 3% at day 7 of DI). Total peripheral resistance and indices of cardiovascular autonomic control were not modified. In conclusion, unchanged autonomic control and total peripheral resistance suggest that increased skin vasoconstriction to standing involves rather local mechanisms-as venoarteriolar reflex-and might compensate insufficient vasoconstriction of other vascular beds.
2D electrophoresis (2-DE) is still a widely used proteomic method despite the availability of high-throughput approaches for protein identification. However, a literature survey only revealed a relatively small number of 2-DE-based studies of human blood proteome. We critically reviewed comparative 2-DE-based proteomic studies, in which groups of patients under examination involved more than ten individuals. Limitation on the number of samples is explained by the requirement to take into account the individual variation of blood proteome. The scanty amount of statistical data on quantitative variations of normal blood proteome may be one of the reasons for the poor applicability of proteomic biomarkers in clinical diagnostics.
Smooth muscle alpha actin (SMA) is a cytoskeletal protein expressed by mesenchymal and smooth muscle cell types, including mural cells (vascular smooth muscle cells and pericytes). Using Bacterial Artificial Chromosome (BAC) recombineering technology, we generated transgenic reporter mice that express a membrane localized cherry red fluorescent protein (mCherry), driven by the full-length SMA promoter and intronic sequences. We determined that the founders and F1 progeny of five independent lines contain 1-3 copies of the mCherry-substituted BAC vector. Furthermore, we characterized the expression of SMA-mCherry in relation to endogenous SMA in the embryo and in adult tissues, and found that the transgenic reporter in each line recapitulated endogenous SMA expression at all time points. We were also able to isolate SMA expressing cells from embryonic tissues using fluorescence-activated cell sorting (FACS). We demonstrated that this marker can be combined with other vital fluorescent reporters and it can be used for live imaging of embryonic cardiodynamics. Therefore, these transgenic mice will be useful for isolating live SMA-expressing cells via FACS and for studying the emergence, behavior, and regulation of SMA-expressing cells, including vascular smooth muscle cells and pericytes throughout embryonic and postnatal development.
A sedentary lifestyle has adverse effects on the cardiovascular system, including impaired endothelial functions. Subjecting healthy men to 7 days of dry immersion (DI) presented a unique opportunity to analyze the specific effects of enhanced inactivity on the endothelium. We investigated endothelial properties before, during, and after 7 days of DI involving eight subjects. Microcirculatory functions were assessed with laser Doppler in the skin of the calf. We studied basal blood flow and endothelium-dependent and -independent vasodilation. We also measured plasma levels of microparticles, a sign of cellular dysfunction, and soluble endothelial factors, reflecting the endothelial state. Basal flow and endothelium-dependent vasodilation were reduced by DI (22 + or - 4 vs. 15 + or - 2 arbitrary units and 29 + or - 6% vs. 12 + or - 6%, respectively, P < 0.05), and this was accompanied by an increase in circulating endothelial microparticles (EMPs), which was significant on day 3 (42 + or - 8 vs. 65 + or - 10 EMPs/microl, P < 0.05), whereas microparticles from other cell origins remained unchanged. Plasma soluble VEGF decreased significantly during DI, whereas VEGF receptor 1 and soluble CD62E were unchanged, indicating that the increase in EMPs was associated with a change in antiapoptotic tone rather than endothelial activation. Our study showed that extreme physical inactivity in humans induced by 7 days of DI causes microvascular impairment with a disturbance of endothelial functions, associated with a selective increase in EMPs. Microcirculatory endothelial dysfunction might contribute to cardiovascular deconditioning as well as to hypodynamia-associated pathologies. In conclusion, the endothelium should be the focus of special care in situations of acute limitation of physical activity.
Recent progress in optical coherence tomography (OCT) allows imaging dynamic structures and fluid flow within scattering tissue, such as the beating heart and blood flow in mouse embryos. Accurate representation and analysis of these dynamic behaviors require reducing the noise of the acquired data. Although noise can be reduced by averaging multiple neighboring pixels in space or time, such operations reduce the effective spatial or temporal resolution that can be achieved. We have developed a computational postprocessing technique to restore image sequences of cyclically moving structures that preserves frame rate and spatial resolution. The signal-to-noise ratio (SNR) is improved by combining images from multiple cycles that have been synchronized with a temporally elastic registration procedure. Here we show how this technique can be applied to OCT images of the circulatory system in cultured mouse embryos. Our technique significantly improves the SNR while preserving temporal and spatial resolution.
The rat has long been considered an excellent system to study mammalian embryonic cardiovascular physiology, but has lacked the extensive genetic tools available in the mouse to be able to create single gene mutations. However, the recent establishment of rat embryonic stem cell lines facilitates the generation of new models in the rat embryo to link changes in physiology with altered gene function to define the underlying mechanisms behind congenital cardiovascular birth defects. Along with the ability to create new rat genotypes there is a strong need for tools to analyze phenotypes with high spatial and temporal resolution. Doppler OCT has been previously used for 3-D structural analysis and blood flow imaging in other model species. We use Doppler swept-source OCT for live imaging of early postimplantation rat embryos. Structural imaging is used for 3-D reconstruction of embryo morphology and dynamic imaging of the beating heart and vessels, while Doppler-mode imaging is used to visualize blood flow. We demonstrate that Doppler swept-source OCT can provide essential information about the dynamics of early rat embryos and serve as a basis for a wide range of studies on functional evaluation of rat embryo physiology.
The most common and lethal birth defects affect the cardiovascular (CV) system. The mouse is a superior model for identifying and understanding mammalian CV birth defects, but there is a great need for tools that can detect early and subtle deficiencies in cardiac function in mouse embryos. We combined swept source optical coherence tomography (SS-OCT) with live mouse embryo culture protocols to generate structural two-dimensional and three-dimensional imaging and hemodynamic measurements in a live 8.5 day embryo just a few hours after the beginning of a heartbeat. Our data show that individual circulating blood cells can be visualized with structural SS-OCT, and using Doppler SS-OCT the velocity of single moving blood cells were measured during different phases of the heartbeat cycle. These results demonstrate that Doppler SS-OCT is an extremely useful tool for structural and hemodynamic analysis at the earliest stages of mammalian blood circulation.
The highly vascularized mouse eye is an excellent model system in which to elucidate the molecular genetic basis of blood vessel development and disease. However, the analysis of ocular vessel defects has traditionally been derived from fixed tissue, which fails to account for dynamic events such as blood flow and cell migration. To overcome the limitations of static analysis, tremendous advances in imaging technology and fluorescent protein reporter mouse lines now enable the direct visualization of developing cells in vivo. Here, we demonstrate that the Flk1-myr::mCherry transgenic mouse is an extremely useful live reporter with broad applicability to retinal, hyaloid, and choroid vascular research.
The development of the cardiovascular system is a highly dynamic process dependent on multiple signaling pathways regulating proliferation, differentiation, migration, cell-cell and cell-matrix interactions. To characterize cell and tissue dynamics during the formation of the cardiovascular system in mice, we generated a novel transgenic mouse line, Tg(Flk1::myr-mCherry), in which endothelial cell membranes are brightly labeled with mCherry, a red fluorescent protein. Tg(Flk1::myr-mCherry) mice are viable, fertile, and do not exhibit any developmental abnormalities. High levels of mCherry are expressed in the embryonic endothelium and endocardium, and expression is also observed in capillaries in adult animals. Targeting of the fluorescent protein to the cell membrane allows for subcellular imaging and cell tracking. By acquiring confocal time lapses of live embryos cultured on the microscope stage, we demonstrate that the newly generated transgenic model beautifully highlights the sprouting behaviors of endothelial cells during vascular plexus formation. We have also used embryos from this line to imaging the endocardium in the beating embryonic mouse heart, showing that Tg(Flk1::myr-mCherry) mice are suitable for the characterization of cardio dynamics. Furthermore, when combined with the previously described Tg(Flk1::H2B-EYFP) line, cell number in addition to cell architecture is revealed, making it possible to determine how individual endothelial cells contribute to the structure of the vessel.
Early embryonic imaging of cardiovascular development in mammalian models requires a method that can penetrate through and distinguish the many tissue layers with high spatial and temporal resolution. In this paper we evaluate the capability of Optical Coherence Tomography (OCT) technique for structural 3D embryonic imaging in mouse embryos at different stages of the developmental process ranging from 7.5 dpc up to 10.5 dpc. Obtained results suggest that the collected data is suitable for quantitative and qualitative measurements to assess cardiovascular function in mouse models, which is likely to expand our knowledge of the complexity of the embryonic heart, and its development into an adult heart.
Mouse models of ocular diseases provide a powerful resource for exploration of molecular regulation of eye development and pre-clinical studies. Availability of a live high-resolution imaging method for mouse embryonic eyes would significantly enhance longitudinal analyses and high-throughput morphological screening. We demonstrate that optical coherence tomography (OCT) can be used for live embryonic ocular imaging throughout gestation. At all studied stages, the whole eye is within the imaging distance of the system and there is a good optical contrast between the structures. We also performed OCT eye imaging in the embryonic retinoblastoma mouse model Pax6-SV40 T-antigen, which spontaneously forms lens and retinal lesions, and demonstrate that OCT allows us to clearly differentiate between the mutant and wild type phenotypes. These results demonstrate that OCTin utero imaging is a potentially useful tool to study embryonic ocular diseases in mouse models.
Current methods to build dynamic optical coherence tomography (OCT) volumes of the beating embryonic heart involve synchronization of 2D+time slice-sequences acquired over separate heartbeats. Temporal registration of these sequences is performed either through gating or postprocessing. While synchronization algorithms that exclusively rely on image- intrinsic signals allow forgoing external gating hardware, they are prone to error accumulation, require operator-supervised correction, or lead to nonisotropic resolution. Here, we propose an image-based, retrospective reconstruction technique that uses two sets of parallel 2D+T slice-sequences, acquired perpendicularly to each other, to yield accurate and automatic reconstructions with isotropic resolution. The method utilizes the similarity of the data at the slice intersections to spatio-temporally register the two sets of slice sequences and fuse them into a high-resolution 4D volume. We characterize our method by using 1) simulated heart phantom datasets and 2) OCT datasets acquired from the beating heart of live cultured E9.5 mouse and E10.5 rat embryos. We demonstrate that while our method requires greater acquisition and reconstruction time compared to methods that use slices from a single direction, it produces more accurate and self-validating reconstructions since each set of reconstructed slices acts as a reference for the slices in the perpendicular set.
Early development of the mammalian cardiovascular system is a highly dynamic process. Live imaging is an essential tool for analyzing normal and abnormal cardiovascular development and dynamics. This article describes two optical approaches for live dynamic imaging of mouse embryonic cardiovascular development: confocal microscopy and optical coherence tomography (OCT). Confocal microscopy, used in combination with fluorescent protein reporter lines, enables visualization of the developing and remodeling cardiovascular system with submicron resolution and even allows visualization of subcellular details of labeled structures. We describe mouse transgenic lines that can be used to image the developing vasculature and characterize hemodynamics by tracking individual blood cells. Confocal microscopy of vital fluorescent markers reveals unique details about cell morphogenesis and movement; however, the imaging depth of this method is limited to ?200 µm. This limitation can be addressed by using OCT, which allows three-dimensional (3D) imaging millimeters into tissue, although this is achieved at the expense of lower spatial resolution (2-10 µm). We describe here how OCT can be applied to the structural analysis of developing mouse embryos and hemodynamic analysis in deep embryonic vessels. These complementary approaches can be used to analyze cardiovascular defects in mutant animals to understand genetic signaling pathways regulating human development.
The most accepted animal model for simulation of the physiological and morphological consequences of microgravity on the cardiovascular system is one of head-down hindlimb unloading. Experimental conditions surrounding this model include not only head-down tilting of rats, but also social and restraint stresses that have their own influences on cardiovascular system function. Here, we studied levels of spontaneous locomotor activity, blood pressure, and heart rate during 14 days under the following experimental conditions: cage control, social isolation in standard rat housing, social isolation in special cages for hindlimb unloading, horizontal attachment (restraint), and head-down hindlimb unloading. General activity and hemodynamic parameters were continuously monitored in conscious rats by telemetry. Heart rate and blood pressure were both evaluated during treadmill running to reveal cardiovascular deconditioning development as a result of unloading. The main findings of our work are that: social isolation and restraint induced persistent physical inactivity, while unloading in rats resulted in initial inactivity followed by normalization and increased locomotion after one week. Moreover, 14 days of hindlimb unloading showed significant elevation of blood pressure and slight elevation of heart rate. Hemodynamic changes in isolated and restrained rats largely reproduced the trends observed during unloading. Finally, we detected no augmentation of tachycardia during moderate exercise in rats after 14 days of unloading. Thus, we concluded that both social isolation and restraint, as an integral part of the model conditions, contribute essentially to cardiovascular reactions during head-down hindlimb unloading, compared to the little changes in the hydrostatic gradient.
Live confocal microscopy of vital fluorescent markers, expressed in mouse embryonic tissues, is a powerful and exciting method to study mammalian embryonic development. This chapter discusses imaging approaches to visualize and characterize dynamic changes of the yolk-sac vasculature and blood flow in mouse embryos. We describe static embryo-culture protocols, which allow maintaining early mouse embryos on the imaging stage for over 24 h. We also describe vital fluorescent-reporter lineages, which can be used to image the developing vasculature and characterize hemodynamics by tracking individual blood cells. Imaging approaches described in this chapter can be used to analyze cardiovascular defects in mutant animals and can provide insights into understanding how genetic signaling pathways and physiological inputs regulate development.
Optical coherence tomography allows for dynamic, three-dimensional (3D+T) imaging of the heart within animal embryos. However, direct 3D+T imaging frame rates remain insufficient for cardiodynamic analysis. Previously, this limitation has been addressed by reconstructing 3D+T representations of the beating heart based on sets of two-dimensional image sequences (2D+T) acquired sequentially at high frame rate and in fixed (and parallel) planes throughout the heart. These methods either require additional hardware to trigger the acquisition of each 2D+T series to the same phase of the cardiac cycle or accumulate registration errors as the slices are synchronized retrospectively by pairs, without a gating signal. Here, we present a sequential turning acquisition and reconstruction (STAR) method for 3D+T imaging of periodically moving structures, which does not require any additional gating signal and is not prone to registration error accumulation. Similarly to other sequential cardiac imaging methods, multiple fast image series are consecutively acquired for different sections but in between acquisitions, the imaging plane is rotated around the center line instead of shifted along the direction perpendicular to the slices. As the central lines of all image-sequences coincide and represent measurements of the same spatial position, they can be used to accurately synchronize all the slices to a single inherent reference signal. We characterized the accuracy of our method on a simulated dynamic phantom and successfully imaged a beating embryonic rat heart. Potentially, this method can be applied for structural or Doppler imaging approaches with any direct space imaging modality such as computed tomography, ultrasound, or light microscopy.
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