Three-dimensional imaging of vasculature and parenchyma in intact rodent organs with X-ray micro-CT

Microcomputed tomography visualization and quantitation of the pulmonary arterial microvascular tree in mouse models of chronic lung disease

Pulmonary vascular dysfunction is characterized by remodeling and loss of microvessels in the lung and is a major manifestation of chronic lung diseases (CLD). In murine models of CLD, the small arterioles and capillaries are the first and most prevalent vessels that are affected by pruning and remodeling. Thus, visualization of the pulmonary arterial vasculature in three dimensions is essential to define pruning and remodeling both temporally and spatially and its role in the pathogenesis of CLD, aging, and tissue repair. To this end, we have developed a novel method to visualize and quantitate the murine pulmonary arterial circulation using microcomputed tomography (µCT) imaging. Using this perfusion technique, we can quantitate microvessels to approximately 6 µM in diameter. We hypothesize that bleomycin-induced injury would have a significant impact on the arterial vascular structure. As proof of principle, we demonstrated that as a result of bleomycin-induced injury at peak fibrosis, significant alterations in arterial vessel structure were visible in the three-dimensional models as well as quantification. Thus, we have successfully developed a perfusion methodology and complementary analysis techniques, which allows for the reconstruction, visualization, and quantitation of the mouse pulmonary arterial microvasculature in three-dimensions. This tool will further support the examination and understanding of angiogenesis during the development of CLD as well as repair following injury.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

3D Transcranial Ultrasound Localization Microscopy in the Rat Brain with a Multiplexed Matrix Probe

OBJECTIVE

Ultrasound Localization Microscopy (ULM) provides images of the microcirculation in-depth in living tissue. However, its implementation in two-dimension is limited by the elevation projection and tedious plane-by-plane acquisition. Volumetric ULM alleviates these issues and can map the vasculature of entire organs in one acquisition with isotropic resolution. However, its optimal implementation requires many independent acquisition channels, leading to complex custom hardware.

METHODS

In this article, we implemented volumetric ultrasound imaging with a multiplexed 32 x 32 probe driven by a single commercial ultrasound scanner. We propose and compare three different sub-aperture multiplexing combinations for localization microscopy in silico and in vitro with a flow of microbubbles in a canal. Finally, we evaluate the approach for micro-angiography of the rat brain.The "light" combination allows a higher maximal volume rate than the "full" combination while maintaining the field of view and resolution.

RESULTS

In the rat brain, 100,000 volumes were acquired within 7 min with a dedicated ultrasound sequence and revealed vessels down to 31 m in diameter with flows from 4.3 mm/s to 28.4 mm/s.

CONCLUSION

This work demonstrates the ability to perform a complete angiography with unprecedented resolution in the living rats brain with a simple and light setup through the intact skull.

SIGNIFICANCE

We foresee that it might contribute to democratize 3D ULM for both preclinical and clinical studies.

Automatic Quantification of Atherosclerosis in Contrast-Enhanced MicroCT Scans of Mouse Aortas Ex Vivo

Objective

While microCT evaluation of atherosclerotic lesions in mice has been formally validated, existing image processing methods remain undisclosed. We aimed to develop and validate a reproducible image processing workflow based on phosphotungstic acid-enhanced microCT scans for the volumetric quantification of atherosclerotic lesions in entire mouse aortas. Approach and Results. 42 WT and 42 apolipoprotein E knockout mouse aortas were scanned. The walls, lumen, and plaque objects were segmented using dual-threshold algorithms. Aortic and plaque volumes were computed by voxel counting and lesion surface by triangulation. The results were validated against manual and histological evaluations. Knockout mice had a significant increase in plaque volume compared to wild types with a plaque to aorta volume ratio of 0.3%, 2.8%, and 9.8% at weeks 13, 18, and 26, respectively. Automatic segmentation correlated with manual (r ² ≥ 0.89; p < .001) and histological evaluations (r ² > 0.96; p < .001).

Conclusions

The semiautomatic workflow enabled rapid quantification of atherosclerotic plaques in mice with minimal manual work.

Imaging the Renal Microcirculation in Cell Therapy

Renal microvascular rarefaction plays a pivotal role in progressive kidney disease. Therefore, modalities to visualize the microcirculation of the kidney will increase our understanding of disease mechanisms and consequently may provide new approaches for evaluating cell-based therapy. At the moment, however, clinical practice is lacking non-invasive, safe, and efficient imaging modalities to monitor renal microvascular changes over time in patients suffering from renal disease. To emphasize the importance, we summarize current knowledge of the renal microcirculation and discussed the involvement in progressive kidney disease. Moreover, an overview of available imaging techniques to uncover renal microvascular morphology, function, and behavior is presented with the associated benefits and limitations. Ultimately, the necessity to assess and investigate renal disease based on in vivo readouts with a resolution up to capillary level may provide a paradigm shift for diagnosis and therapy in the field of nephrology.

Impaired Hedgehog-Gli1 Pathway Activity Underlies the Vascular Phenotype of Polycystic Kidney Disease

Polycystic kidney disease (PKD) has been linked to abnormal structure/function of ciliary proteins, leading to renal dysfunction. Recently, attention has been focused in the significant vascular abnormalities associated with PKD, but the mechanisms underlying this phenomenon remain elusive. Here, we seek to define the molecular events regulating the angiogenic imbalance observed in PKD. Using micro computed tomography (n=7) and protein expression analysis (n=5), we assessed the vascular density and the angiogenic profile of noncystic organs in a well-established PKD rat model (Polycystic Kidney-PCK rat). Heart and lungs of PCK rats have reduced vascular density and decreased expression of angiogenic factors compared with wild type. Similarly, PCK-vascular smooth muscle cells (VSMCs; n=4) exhibited lower levels of vascular markers. Then, using small interfering RNA (n=4), we determined the role of the ciliary protein fibrocystin in wild type-VSMCs, a critical component/regulator of vascular structure and function. Reduction of fibrocystin in wild type-VSMCs (n=4) led to an abnormal angiogenic potential similar to that observed in PCK-VSMCs. Furthermore, we investigated the involvement of the hedgehog signaling, a pathway closely linked to the primary cilium and associated with vascular development, in PKD. Mechanistically, we demonstrated that impairment of the hedgehog signaling mediates, in part, this abnormal angiogenic phenotype. Lastly, overexpression of Gli1 in PCK-VSMCs (n=4) restored the expression levels of proangiogenic molecules. Our data support a critical role of fibrocystin in the abnormal vascular phenotype of PKD and indicate that a dysregulation of hedgehog may be responsible, at least in part, for these vascular deficiencies.

In vivo quantification of mandibular bone remodeling and vascular changes in a Wistar rat model: A novel HR-MRI and micro-CT fusion technique

Purpose

This study was performed to introduce an in vivo hybrid multimodality technique involving the coregistration of micro-computed tomography (micro-CT) and high-resolution magnetic resonance imaging (HR-MRI) to concomitantly visualize and quantify mineralization and vascularization at follow-up in a rat model.

Materials and Methods

Three adult female rats were randomly assigned as test subjects, with 1 rat serving as a control subject. For 20 weeks, the test rats received a weekly intravenous injection of 30 µg/kg zoledronic acid, and the control rat was administered a similar dose of normal saline. Bilateral extraction of the lower first and second molars was performed after 10 weeks. All rats were scanned once every 4 weeks with both micro-CT and HR-MRI. Micro-CT and HR-MRI images were registered and fused in the same 3-dimensional region to quantify blood flow velocity and trabecular bone thickness at T0 (baseline), T4 (4 weeks), T8 (8 weeks), T12 (12 weeks), T16 (16 weeks), and T20 (20 weeks). Histological assessment was the gold standard with which the findings were compared.

Results

The histomorphometric images at T20 aligned with the HR-MRI findings, with both test and control rats demonstrating reduced trabecular bone vasculature and blood vessel density. The micro-CT findings were also consistent with the histomorphometric changes, which revealed that the test rats had thicker trabecular bone and smaller marrow spaces than the control rat.

Conclusion

The combination of micro-CT and HR-MRI may be considered a powerful non-invasive novel technique for the longitudinal quantification of localized mineralization and vascularization.

Aqueous outflow imaging techniques and what they tell us about intraocular pressure regulation

Recent advances in the medical and surgical management of open-angle glaucoma have increased the number of treatment options available. Several new intraocular pressure (IOP)-lowering treatments target the conventional aqueous outflow (AO) system. However, success rates are variable and outcomes in individual patients are often difficult to predict. Variable treatment responses remain unexplained and highlight deficiencies in our current understanding of AO regulation and IOP homeostasis. Imaging is often relied upon to confirm diagnoses and monitor treatment responses in other ocular and systemic pathologies. As yet no suitable AO imaging tool has been developed to fulfil this role in glaucoma. A variety of imaging techniques have been used to study the AO tracts of humans and animals in ex vivo and in vivo eyes. In this review, results from novel imaging techniques that assess aqueous drainage through the episcleral venous system are considered and we argue these provide new insights into AO regulation. We suggest that the ability to objectively measure AO responses to interventions would be a significant clinical advance, and we have demonstrated that this can be achieved with direct visualisation of aqueous drainage. We predict that the evolution of AO imaging technology will continue to reveal critical components of AO and IOP regulation, and that personalised IOP-lowering treatment in glaucoma care may well become a reality in the near future.

Development of barium-based low viscosity contrast agents for micro CT vascular casting: Application to 3D visualization of the adult mouse cerebrovasculature

Recent advances in three-dimensional (3D) fluorescence microscopy offer the ability to image the entire vascular network in entire organs, or even whole animals. However, these imaging modalities rely on either endogenous fluorescent reporters or involved immunohistochemistry protocols, as well as optical clearing of the tissue and refractive index matching. Conversely, X-ray-based 3D imaging modalities, such as micro CT, can image non-transparent samples, at high resolution, without requiring complicated or expensive immunolabeling and clearing protocols, or fluorescent reporters. Here, we compared two "homemade" barium-based contrast agents to the field standard, lead-containing Microfil, for micro-computed tomography (micro CT) imaging of the adult mouse cerebrovasculature. The perfusion pressure required for uniform vessel filling was significantly lower with the barium-based contrast agents compared to the polymer-based Microfil. Accordingly, the barium agents showed no evidence of vascular distension or rupture, common problems associated with Microfil. Compellingly, perfusion of an aqueous BaCl₂ /gelatin mixture yielded equal or superior visualization of the cerebrovasculature by micro CT compared to Microfil. However, phosphate-containing buffers and fixatives were incompatible with BaCl₂ due to the formation of unwanted precipitates. X-ray attenuation of the vessels also decreased overtime, as the BaCl₂ appeared to gradually diffuse into surrounding tissues. A second, unique formulation composed of BaSO₄ microparticles, generated in-house by mixing BaCl₂ and MgSO₄ , suffered none of these drawbacks. These microparticles, however, were unable to pass small diameter capillary vessels, conveniently labeling only the arterial cerebrovasculature. In summary, we present an affordable, robust, low pressure, non-toxic, and straightforward methodology for 3D visualization of the cerebrovasculature.

SLIME: robust, high-speed 3D microvascular mapping

Three dimensional (3D) microvascular imaging of cubic millimeter to centimeter size volumes often requires much time and expensive instruments. By combining optical clearing with a novel scatter-based optical coherence tomography (OCT) contrast agent, we have greatly extended OCT imaging depth in excised tissues while maintaining a simple and low cost approach that does not require in-depth OCT knowledge. The new method enables fast 3D microvascular mapping in large tissue volumes, providing a promising tool for investigating organ level microvascular abnormalities in large cohorts.

Correlative Detection of Isolated Single and Multi-Cellular Calcifications in the Internal Elastic Lamina of Human Coronary Artery Samples

Histopathology protocols often require sectioning and processing of numerous microscopy slides to survey a sample. Trade-offs between workload and sampling density means that small features can be missed. Aiming to reduce the workload of routine histology protocols and the concern over missed pathology in skipped sections, we developed a prototype x-ray tomographic scanner dedicated to rapid scouting and identification of regions of interest in pathology specimens, thereby allowing targeted histopathology analysis to replace blanket searches. In coronary artery samples of a deceased HIV patient, the scanner, called Tomopath, obtained depth-resolved cross-sectional images at 15 µm resolution in a 15-minute scan, which guided the subsequent histological sectioning and microscopy. When compared to a commercial tabletop micro-CT scanner, the prototype provided several-fold contrast-to-noise ratio in 1/11^th the scan time. Correlated tomographic and histological images revealed two types of micro calcifications: scattered loose calcifications typically found in atherosclerotic lesions; isolated focal calcifications in one or several cells in the internal elastic lamina and occasionally in the tunica media, which we speculate were the initiation of medial calcification linked to kidney disease, but rarely detected at this early stage due to their similarity to particle contaminants introduced during histological processing, if not for the evidence from the tomography scan prior to sectioning. Thus, in addition to its utility as a scouting tool, in this study it provided complementary information to histological microscopy. Overall, the prototype scanner represents a step toward a dedicated scouting and complementary imaging tool for routine use in pathology labs.

Gastropod shell size and architecture influence the applicability of methods used to estimate internal volume

Obtaining accurate and reproducible estimates of internal shell volume is a vital requirement for studies into the ecology of a range of shell-occupying organisms, including hermit crabs. Shell internal volume is usually estimated by filling the shell cavity with water or sand, however, there has been no systematic assessment of the reliability of these methods and moreover no comparison with modern alternatives, e.g., computed tomography (CT). This study undertakes the first assessment of the measurement reproducibility of three contrasting approaches across a spectrum of shell architectures and sizes. While our results suggested a certain level of variability inherent for all methods, we conclude that a single measure using sand/water is likely to be sufficient for the majority of studies. However, care must be taken as precision may decline with increasing shell size and structural complexity. CT provided less variation between repeat measures but volume estimates were consistently lower compared to sand/water and will need methodological improvements before it can be used as an alternative. CT indicated volume may be also underestimated using sand/water due to the presence of air spaces visible in filled shells scanned by CT. Lastly, we encourage authors to clearly describe how volume estimates were obtained.

A guide for effective anatomical vascularization studies: useful ex vivo methods for both CT and MRI imaging before dissection

The objective of this study was to develop a simple and useful injection protocol for imaging cadaveric vascularization and dissection. Mixtures of contrast agent and cast product should provide adequate contrast for two types of ex vivo imaging (MRI and CT) and should harden to allow gross dissection of the injected structures. We tested the most popular contrast agents and cast products, and selected the optimal mixture composition based on their availability and ease of use. All mixtures were first tested in vitro to adjust dilution parameters of each contrast agent and to fine-tune MR imaging acquisition sequences. Mixtures were then injected in 24 pig livers and one human pancreas for MR and computed tomography (CT) imaging before anatomical dissection. Colorized latex, gadobutrol and barite mixture met the above objective. Mixtures composed of copper sulfate (CuSO₄ ) gadoxetic acid (for MRI) and iodine (for CT) gave an inhomogeneous signal or extravasation of the contrast agent. Agar did not harden sufficiently for gross dissection but appears useful for CT and magnetic resonance imaging (MRI) studies without dissection. Silicone was very hard to inject but achieved the goals of the study. Resin is particularly difficult to use but could replace latex as an alternative for corrosion instead of dissection. This injection protocol allows CT and MRI images to be obtained of cadaveric vascularization and anatomical casts in the same anatomic specimen. Post-imaging processing software allow easy 3D reconstruction of complex anatomical structures using this technique. Applications are numerous, e.g. surgical training, teaching methods, postmortem anatomic studies, pathologic studies, and forensic diagnoses.

Whole organ vascular casting and microCT examination of the human placental vascular tree reveals novel alterations associated with pregnancy disease

Experimental methods that allow examination of the intact vascular network of large organs, such as the human placenta are limited, preventing adequate comparison of normal and abnormal vascular development in pregnancy disease. Our aims were (i) to devise an effective technique for three-dimensional analyses of human placental vessels; (ii) demonstrate the utility of the technique in the comparison of placental vessel networks in normal and fetal growth restriction (FGR) complicated pregnancies. Radiopaque plastic vessel networks of normal and FGR placentas (n = 12/group) were created by filling the vessels with resin and corroding the surrounding tissues. Subsequently, each model was scanned in a microCT scanner, reconstructed into three-dimensional virtual objects and analysed in visualisation programmes. MicroCT imaging of the models defined vessel anatomy to our analyses threshold of 100 µm diameter. Median vessel length density was significantly shorter in arterial but longer in venous FGR networks compared to normals. No significant differences were demonstrable in arterial or venous tortuosity, diameter or branch density. This study demonstrates the potential effectiveness of microCT for ex-vivo examination of human placental vessel morphology. Our findings show significant discrepancies in vessel length density in FGR placentas. The effects on fetoplacental blood flow, and hence nutrient transfer to the fetus, are unknown.

Characterization of Continuous and Pulsed Emission modes of a Hybrid Micro Focus X-ray Source for Medical Imaging Applications

The aim of this study was to quantitatively characterize a micro focus x-ray tube that can operate in both continuous and pulsed emission modes. The micro focus x-ray source (Model L9181-06, Hamamatsu Photonics, Japan) has a varying focal spot size ranging from 16-50 μm as the source output power changes from 10-39 W. We measured the source output, beam quality, focal spot sizes, kV accuracy, spectra shapes and spatial resolution. Source output was measured using an ionization chamber for various tube voltages (kVs) with varying current (μA) and distances. The beam quality was measured in terms of half value layer (HVL), kV accuracy was measured with a non-invasive kV meter, and the spectra was measured using a compact integrated spectrometer system. The focal spot sizes were measured using a slit method with a CCD detector with a pixel pitch of 22 μm. The spatial resolution was quantitatively measured using the slit method with a CMOS flat panel detector with a 50 μm pixel pitch, and compared to the qualitative results obtained by imaging a contrast bar pattern. The focal spot sizes in the vertical direction were smaller than that of the horizontal direction, the impact of which was visible when comparing the spatial resolution values. Our analyses revealed that both emission modes yield comparable imaging performances in terms of beam quality, spectra shape and spatial resolution effects. There were no significantly large differences, thus providing the motivation for future studies to design and develop stable and robust cone beam imaging systems for various diagnostic applications.

Depth-resolved 3D visualization of coronary microvasculature with optical microangiography

In this study, we propose a novel implementation of optical coherence tomography-based angiography combined with ex vivo perfusion of fixed hearts to visualize coronary microvascular structure and function. The extracorporeal perfusion of Intralipid solution allows depth-resolved angiographic imaging, control of perfusion pressure, and high-resolution optical microangiography. The imaging technique offers new opportunities for microcirculation research in the heart, which has been challenging due to motion artifacts and the lack of independent control of pressure and flow. With the ability to precisely quantify structural and functional features, this imaging platform has broad potential for the study of the pathophysiology of microvasculature in the heart as well as other organs.

Arterial Wall Perfusion Measured with Photon Counting Spectral X-ray CT

Early atherosclerosis changes perfusion of the arterial wall due to localized proliferation of the vasa vasorum. When contrast agent passes through the artery, some enters the vasa vasorum and increases radiopacity of the arterial wall. Technical challenges to detecting changes in vasa vasorum density include the thin arterial wall, partial volume averaging at the arterial lumen/wall interface and calcification within the wall. We used a photon-counting spectral CT scanner to study carotid arteries of anesthetized pigs and micro-CT of these arteries to quantify vasa vasorum density. The left carotid artery wall was injected with autologous blood to stimulate vasa vasorum angiogenesis. The scans were performed at 25-120 keV; the tube-current-time product was 550 mAs. A 60 mL bolus of iodine contrast agent was injected into the femoral vein at 5mL/s. Two seconds post injection, an axial scan was acquired at every 3 s over 60 s (i.e., 20 time points). Each time point acquired 28 contiguous transaxial slices with reconstructed voxels 0.16 × 0.16 × 1 mm³. Regions-of-interest in the outer 2/3 of the arterial wall and in the middle 2/3 of the lumen were drawn and their enhancements plotted versus time. Lumenal CT values peaked several seconds after injection and then returned towards baseline. Arterial wall CT values peaked concurrent to the lumen. The peak arterial wall enhancement in the left carotid arterial wall correlated with increased vasa vasorum density observed in micro-CT images of the isolated arteries.

Synchrotron Imaging Assessment of Bone Quality

Bone is a complex hierarchical structure, and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence, analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen-mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in situ testing in bone research.

Growth, ageing and scaling laws of coronary arterial trees

Despite the well-known design principles of vascular systems, it is unclear whether the vascular arterial tree obeys some scaling constraints during normal growth and ageing in a given species. Based on the micro-computed tomography measurements of coronary arterial trees in mice at different ages (one week to more than eight months), we show a constant exponent of 3/4, but age-dependent scaling coefficients in a length-volume scaling law (Lc=K(length-volume) · Vc³/⁴; Lc is the crown length, Vc is the crown volume, K(length-volume) is the age-dependent scaling coefficient) during normal growth and ageing. The constant 3/4 exponent represents the self-similar fractal-like branching pattern (i.e. basic mechanism to regulate the development of vascular trees within a species), whereas the age-dependent scaling coefficients characterize the structural growth or resorption of vascular trees during normal growth or ageing, respectively. This study enhances the understanding of age-associated changes in vascular structure and function.

Effect of intraspecimen spatial variation in tissue mineral density on the apparent stiffness of trabecular bone

This study investigated the effects of intraspecimen variations in tissue mineral density(TMD) on the apparent-level stiffness of human trabecular bone. High-resolution finite element (FE) models were created for each of 12 human trabecular bone specimens,using both microcomputed tomography (lCT) and “gold-standard” synchrotron radiation lCT (SRlCT) data. Our results confirm that incorporating TMD spatial variation reduces the calculated apparent stiffness compared to homogeneous TMD models. This effect exists for both lCT- and SRlCT-based FE models, but is exaggerated in lCT based models. This study provides a direct comparison of lCT to SRlCT data and is thereby able to conclude that the influence of including TMD heterogeneity is overestimated in lCT-based models.

Myocardial Perfusion: Characteristics of Distal Intramyocardial Arteriolar Trees

A combination of experimental, theoretical, and imaging methodologies is used to examine the hierarchical structure and function of intramyocardial arteriolar trees in porcine hearts to provide a window onto a region of myocardial microvasculature which has been difficult to fully explore so far. A total of 66 microvascular trees from 6 isolated myocardial specimens were analyzed, with a cumulative number of 2438 arteriolar branches greater than or equal to 40 μm lumen diameter. The distribution of flow rates within each tree was derived from an assumed power law relationship for that tree between the diameter of vessel segments and flow rates that are consistent with that power law and subject to conservation of mass along hierarchical structure of the tree. The results indicate that the power law index increases at levels of arteriolar vasculature closer to the capillary level, consistent with a concomitant decrease in shear stress acting on endothelial tissue. These results resolve a long standing predicament which could not be resolved previously because of lack of data about the 3D, interconnected, arterioles. In the context of myocardial perfusion, the results indicate that the coefficient of variation of flow rate in pre-capillary distal arterioles is high, suggesting that heterogeneity of flow rate in these arterioles is not entirely random but may be due at least in part to active control.

NUFFT-Based Iterative Image Reconstruction via Alternating Direction Total Variation Minimization for Sparse-View CT

Sparse-view imaging is a promising scanning method which can reduce the radiation dose in X-ray computed tomography (CT). Reconstruction algorithm for sparse-view imaging system is of significant importance. The adoption of the spatial iterative algorithm for CT image reconstruction has a low operation efficiency and high computation requirement. A novel Fourier-based iterative reconstruction technique that utilizes nonuniform fast Fourier transform is presented in this study along with the advanced total variation (TV) regularization for sparse-view CT. Combined with the alternating direction method, the proposed approach shows excellent efficiency and rapid convergence property. Numerical simulations and real data experiments are performed on a parallel beam CT. Experimental results validate that the proposed method has higher computational efficiency and better reconstruction quality than the conventional algorithms, such as simultaneous algebraic reconstruction technique using TV method and the alternating direction total variation minimization approach, with the same time duration. The proposed method appears to have extensive applications in X-ray CT imaging.

Earl Wood--a research career noted for development of novel instruments driven by the power of the indicator dilution concept

During World War 2, Earl Wood was charged with elucidating the biomedical factors in acceleration-induced loss of consciousness experienced by pilots in high-performance aircraft. For this, he developed devices for measurement and recording of blood pressure and tissue blood content. Those data lead to the design and fabrication of successful countermeasures to acceleration-induced loss of consciousness with an inflatable "G-suit" and "M1" breath-holding maneuver. After World War 2, he utilized and modified these instruments and made use of indicator dilution techniques by continuous intracardiac blood sampling to greatly increase the specificity and sensitivity of diagnosis of intracardiac anatomic and functional abnormalities in patients with congenital heart disease. This contributed to the greatly increased success rate of open-heart surgery in the 1950s. In the 1960s, he built on the then recently available video-coupled electronic X-ray image intensifier to develop X-ray fluoroscopy-based recording of indicator dilution signals in all cardiac chambers and surrounding great vessels without the need for placing catheter tips at those locations for blood sampling. However, these blood flow-related data were of limited value, as they were not measured concurrent with myocardial functional demand for perfusion. In the 1970s, he overcame this limitation by developing a high-speed multislice X-ray imaging scanner to provide tomographic images of concurrent dynamic cardiac anatomy and the indicator dilution-based estimates of blood flow distributions. On his retirement at age 70 in 1982, he had accomplished his 2 decade-old goal of the ability to make accurate concurrent, minimally invasive, and indicator dilution-based measurement of cardiovascular structure to function relationships.

Twenty-fold acceleration of 3D projection reconstruction MPI

We experimentally demonstrate a 20-fold improvement in acquisition time in projection reconstruction (PR) magnetic particle imaging (MPI) relative to the state-of-the-art PR MPI imaging results. We achieve this acceleration in our imaging system by introducing an additional Helmholtz electromagnet pair, which creates a slow shift (focus) field. Because of magnetostimulation limits in humans, we show that scan time with three-dimensional (3D) PR MPI is theoretically within the same order of magnitude as 3D MPI with a field free point; however, PR MPI has an order of magnitude signal-to-noise ratio gain.

Anatomy of hepatic arteriolo-portal venular shunts evaluated by 3D micro-CT imaging

The liver differs from other organs in that two vascular systems deliver its blood - the hepatic artery and the portal vein. However, how the two systems interact is not fully understood. We therefore studied the microvascular geometry of rat liver hepatic artery and portal vein injected with the contrast polymer Microfil(®). Intact isolated rat livers were imaged by micro-CT and anatomic evidence for hepatic arteriolo-portal venular shunts occurring between hepatic artery and portal vein branches was found. Simulations were performed to rule out the possibility of the observed shunts being artifacts resulting from image blurring. In addition, in the case of specimens where only the portal vein was injected, only the portal vein was opacified, whereas in hepatic artery injections, both the hepatic artery and portal vein were opacified. We conclude that mixing of the hepatic artery and portal vein blood can occur proximal to the sinusoidal level, and that the hepatic arteriolo-portal venular shunts may function as a one-way valve-like mechanism, allowing flow only from the hepatic artery to the portal vein (and not the other way around).

Atherosclerosis and atheroma plaque rupture: imaging modalities in the visualization of vasa vasorum and atherosclerotic plaques

Invasive angiography has been widely accepted as the gold standard to diagnose cardiovascular pathologies. Despite its superior resolution of demonstrating atherosclerotic plaque in terms of degree of lumen stenosis, the morphological assessment for the plaque is insufficient for the analysis of plaque components, and therefore, unable to predict the risk status or vulnerability of atherosclerotic plaque. There is an increased body of evidence to show that the vasa vasorum play an important role in the initiation, progression, and complications of atherosclerotic plaque leading to major adverse cardiac events. This paper provides an overview of the evidence-based reviews of various imaging modalities with regard to their potential value for comprehensive characterization of the composition, burden, and neovascularization of atherosclerotic plaque.

A perfusion procedure for imaging of the mouse cerebral vasculature by X-ray micro-CT

BACKGROUND

Micro-CT is a novel X-ray imaging modality which can provide 3D high resolution images of the vascular network filled with contrast agent. The cerebrovascular system is a complex anatomical structure that can be imaged with contrast enhanced micro-CT. However, the morphology of the cerebrovasculature and many circulatory anastomosis in the brain result in high variations in the extent of contrast agent filling in the blood vessels and as a result, the vasculature of different subjects appear differently in the acquired images. Specifically, the posterior circulation is not consistently perfused with the contrast agent in many brain specimens and thus, many major vessels that perfuse blood to the midbrain and hindbrain are not visible in the micro-CT images acquired from these samples.

NEW METHOD

In this paper, we present a modified surgical procedure of cerebral vasculature perfusion through the left ventricle with Microfil contrast agent, in order to achieve a more uniform perfusion of blood vessels throughout the brain and as a result, more consistent images of the cerebrovasculature. Our method consists of filling the posterior cerebral circulation with contrast agent, followed by the perfusion of the whole cerebrovasculature.

RESULTS

Our histological results show that over 90% of the vessels in the entire brain, including the cerebellum, were filled with contrast agent.

COMPARISON WITH EXISTING METHOD

Our results show that the new technique of sample perfusion decreases the variability of the posterior circulation in the cerebellum in micro-CT images by 6.9%.

CONCLUSIONS

This new technique of sample preparation improves the quality of cerebrovascular images.

Changes in CT angiographic opacification of porcine coronary artery wall with patchy altered flow in vasa vasorum

To evaluate the potential of whole-body CT to detect localized areas of decreased or increased vascularity in coronary arterial walls. We used both microsphere embolization of coronary artery vasa vasorum to generate small areas of hypoperfusion and surrounding hyperperfusion of the arterial wall and diet-induced hypercholesterolemia. As a stimulus for localized angiogenesis, such as occurs in early plaque formation in the coronary arterial wall, microspheres were injected selectively into the LAD coronary artery lumens of anesthetized pigs. Fourteen pigs (acute) then had a segment of their LAD harvested during injection of contrast medium and snap-frozen for subsequent cryo-static micro-CT. An additional thirteen pigs (chronic) were allowed to recover, fed a high cholesterol diet and 3 months later were again anesthetized and a segment of the LAD artery harvested and scanned. The spatial distribution of the contrast agent within the arterial wall was measured in contiguous micro-CT images at right angles to the lumen axis with the area of wall in each cross-sectional image being approximately (0.1 mm)(3) in size. In the acute animals there were no localized areas of increased contrast around the hypoperfused embolized perfusion territories in the arterial wall, but in the chronic animals the hypoperfused areas were surrounded by increased contrast. These results suggest that CT might be able to detect localized regions of increased vascularity in the arterial wall as an indicator of early atherosclerotic stimulation of vasa vasorum proliferation.

Vascularity of myocardium and gastrocnemius muscle in rats selectively bred for endurance running capacity

We tested the hypothesis that changes in the arteriolar branching architecture contributed to increased running capacity of rats subjected to two-way artificial selection for intrinsic aerobic endurance treadmill running capacity resulting in strains of low-capacity and high-capacity endurance rats. Hearts and gastrocnemius muscles were harvested from each strain, and the microvasculature's branching geometry measured from micro-CT images. The vascular branching geometry of the hearts and skeletal muscle from the high capacity was indistinguishable from low-capacity rats. Our hypothesis was not supported. Neither remodeling nor an increase in arteriolar microvasculature branching appears to play a role in the enhanced performance of the high capacity rats. We are led to speculate that endothelial tolerance for shear stress and/or increased coupling of myocardial muscle fiber metabolic-to-contractile function is increased in the high-capacity runner strain to the effect of allowing either higher flow rate per unit volume of muscle or more efficient use of oxygen and nutrients in the high-capacity endurance rats.

3D Imaging of vascular networks for biophysical modeling of perfusion distribution within the heart

One of the main determinants of perfusion distribution within an organ is the structure of its vascular network. Past studies were based on angiography or corrosion casting and lacked quantitative three dimensional, 3D, representation. Based on branching rules and other properties derived from such imaging, 3D vascular tree models were generated which were rather useful for generating and testing hypotheses on perfusion distribution in organs. Progress in advanced computational models for prediction of perfusion distribution has raised the need for more realistic representations of vascular trees with higher resolution. This paper presents an overview of the different methods developed over time for imaging and modeling the structure of vascular networks and perfusion distribution, with a focus on the heart. The strengths and limitations of these different techniques are discussed. Episcopic fluorescent imaging using a cryomicrotome is presently being developed in different laboratories. This technique is discussed in more detail, since it provides high-resolution 3D structural information that is important for the development and validation of biophysical models but also for studying the adaptations of vascular networks to diseases. An added advantage of this method being is the ability to measure local tissue perfusion. Clinically, indices for patient-specific coronary stenosis evaluation derived from vascular networks have been proposed and high-resolution noninvasive methods for perfusion distribution are in development. All these techniques depend on a proper representation of the relevant vascular network structures.

Detection and early phase assessment of radiation-induced lung injury in mice using micro-CT

Radiation therapy is an important therapeutic modality for thoracic malignancies. However, radiation-induced pulmonary injuries such as radiation pneumonitis and fibrosis are major dose-limiting factors. Previous research shows that micro-computed tomography (micro-CT) can detect radiation-induced lung injuries a few months following irradiation, but studies to assess the early response of lung tissue are lacking. The aim of this study was to determine if micro-CT could be used to detect and assess early-phase radiation–induced lung injury in mice. Twenty-one animals were divided into three groups: normal (n = 7), one day after x-ray exposure (n = 7), and at four days after x-ray exposure (n = 7). The x-ray-exposed groups received a single dose of 20 Gy, to the whole lung. Histology showed enlargements of the air space (Lm: mean chord length) following irradiation. 40.5±3.8 µm and 60.0±6.9 µm were observed after one and four days, respectively, compared to 26.5±3.1 µm in normal mice. Three-dimensional micro-CT images were constructed and histograms of radiodensity - Hounsfield Units (HU) - were used to assess changes in mouse lungs. Radiation-induced lung injury was observed in irradiated mice, by the use of two parameters which were defined as shifts in peak HU between −200 to −800 HU (Peak_HU) and increase in the number of pixels at −1000 HU (Number_-1000). These parameters were correlated with histological changes. The results demonstrate that micro-CT can be used for the early detection and assessment of structural and histopathological changes resulting from radiation-induced lung injury in mice. Micro-CT has the advantage, over traditional histological techniques, of allowing longitudinal studies of lung disease progression and assessment of the entire lung, while reducing the number of animals required for such studies.

Optimization-based reconstruction of sparse images from few-view projections

In this work, we investigate optimization-based image reconstruction from few-view (i.e. less than ten views) projections of sparse objects such as coronary-artery specimens. Using optimization programs as a guide, we formulate constraint programs as reconstruction programs and develop algorithms to reconstruct images through solving the reconstruction programs. Characterization studies are carried out for elucidating the algorithm properties of 'convergence' (relative to designed solutions) and 'utility' (relative to desired solutions) by using simulated few-view data calculated from a discrete FORBILD coronary-artery phantom, and real few-view data acquired from a human coronary-artery specimen. Study results suggest that carefully designed reconstruction programs and algorithms can yield accurate reconstructions of sparse images from few-view projections.

Cardiac micro-computed tomography imaging of the aging coronary vasculature

BACKGROUND

Alterations at the level of the coronary circulation with aging may play an important role in the evolution of age-associated changes in left ventricular (LV) fibrosis and function. However these age-associated changes in the coronary vasculature remain poorly defined primarily due to the lack of high resolution imaging technologies. The current study was designed to utilize cardiac micro-computed tomography (micro-CT) technology as a novel imaging strategy, to define the 3-dimensional coronary circulation in the young and aged heart and its relationship to LV fibrosis and function.

METHODS AND RESULTS

Young (2 months old; n=10) and aged (20 months old; n=10) Fischer rats underwent cardiac micro-CT imaging as well as echocardiography, blood pressure, and fibrosis analysis. Importantly, when indexed to LV mass, which increased with age, the total and intramyocardial vessel volumes were lower, whereas the epicardial vessel volume, with and without indexing to LV mass, was significantly higher in the aged hearts compared with the young hearts. Moreover, the aged hearts had a significantly lower percentage of intramyocardial vessel volume and a significantly higher percentage of epicardial vessel volume, when normalized to the total vessel volume, compared with the young hearts. Further, the aged hearts had significant LV fibrosis and mild LV dysfunction compared with the young hearts.

CONCLUSIONS

This micro-CT imaging study reports the reduction in normalized intramyocardial vessel volume within the aged heart, in association with increased epicardial vessel volume, in the setting of increased LV fibrosis, and mild LV dysfunction.

Retrograde perfusion and filling of mouse coronary vasculature as preparation for micro computed tomography imaging

Visualization of the vasculature is becoming increasingly important for understanding many different disease states. While several techniques exist for imaging vasculature, few are able to visualize the vascular network as a whole while extending to a resolution that includes the smaller vessels. Additionally, many vascular casting techniques destroy the surrounding tissue, preventing further analysis of the sample. One method which circumvents these issues is micro-Computed Tomography (μCT). μCT imaging can scan at resolutions <10 microns, is capable of producing 3D reconstructions of the vascular network, and leaves the tissue intact for subsequent analysis (e.g., histology and morphometry). However, imaging vessels by ex vivo μCT methods requires that the vessels be filled with a radiopaque compound. As such, the accurate representation of vasculature produced by μCT imaging is contingent upon reliable and complete filling of the vessels. In this protocol, we describe a technique for filling mouse coronary vessels in preparation for μCT imaging. Two predominate techniques exist for filling the coronary vasculature: in vivo via cannulation and retrograde perfusion of the aorta (or a branch off the aortic arch), or ex vivo via a Langendorff perfusion system. Here we describe an in vivo aortic cannulation method which has been specifically designed to ensure filling of all vessels. We use a low viscosity radiopaque compound called Microfil which can perfuse through the smallest vessels to fill all the capillaries, as well as both the arterial and venous sides of the vascular network. Vessels are perfused with buffer using a pressurized perfusion system, and then filled with Microfil. To ensure that Microfil fills the small higher resistance vessels, we ligate the large branches emanating from the aorta, which diverts the Microfil into the coronaries. Once filling is complete, to prevent the elastic nature of cardiac tissue from squeezing Microfil out of some vessels, we ligate accessible major vascular exit points immediately after filling. Therefore, our technique is optimized for complete filling and maximum retention of the filling agent, enabling visualization of the complete coronary vascular network--arteries, capillaries, and veins alike.

Quantitative imaging of cartilage and bone morphology, reactive oxygen species, and vascularization in a rodent model of osteoarthritis

OBJECTIVE

To assess temporal changes in cartilage and bone morphology, reactive oxygen species (ROS), and vascularization in rats with monosodium iodoacetate (MIA)-induced osteoarthritis (OA), using advanced imaging methodologies.

METHODS

Right knees of 8-week-old male Wistar rats were injected with 1 mg MIA in 50 μl saline and left knees were injected with 50 μl saline as controls. After 1, 2, and 3 weeks (n = 5 at each time point), changes in cartilage morphology and composition were quantified using equilibrium partitioning of an ionic contrast agent microfocal computed tomography (μCT), and changes in subchondral and trabecular bone were assessed by standard μCT. ROS were characterized by in vivo fluorescence imaging at 1, 11, and 21 days (n = 5 at each time point). Three weeks following fluorescence imaging, alterations in knee joint vascularity were quantified with μCT after perfusion of a vascular contrast agent.

RESULTS

Femoral cartilage volume, thickness, and proteoglycan content were significantly decreased in MIA-injected knees compared with control knees, accompanied by loss of trabecular bone and erosion of subchondral bone surface. ROS quantities were significantly increased 1 day after MIA injection and subsequently decreased gradually, having returned to normal by 21 days. Vascularity in whole knees and distal femora was significantly increased at 21 days after MIA injection.

CONCLUSION

Contrast-enhanced μCT and fluorescence imaging were combined to characterize articular cartilage, subchondral bone, vascularization, and ROS, providing unprecedented 3-dimensional joint imaging and quantification in multiple tissues during OA progression. These advanced imaging techniques have the potential to become standardized methods for comprehensive evaluation of articular joint degeneration and evaluation of therapeutic efficacy.

Evaluation of bone scaffolds by micro-CT

This paper reviews the possibilities offered by X-ray micro-CT in bone tissue engineering. This technique provides a fast, nondestructive, and 3D quantification of bone scaffolds, bone ingrowth, and microvascularization. Synchrotron radiation absorption and phase micro-CT offer additional advantages to image newly formed bone in bioceramic scaffolds and pre-bone matrix.

Relationship between surface area of nonperfused myocardium and extravascular extraction of contrast agent following coronary microembolization

Myocardial microvascular permeability and coronary sinus concentration of muscle metabolites have been shown to increase after myocardial ischemia due to epicardial coronary artery occlusion and reperfusion. However, their association with coronary microembolization is not well defined. This study tested the hypothesis that acute coronary microembolization increases microvascular permeability in the porcine heart. The left anterior descending perfusion territories of 34 anesthetized pigs (32 ± 3 kg) were embolized with equal volumes of microspheres of one of three diameters (10, 30, or 100 μm) and at three different doses for each size. Electron beam computed tomography (EBCT) was used to assess in vivo, microvascular extraction of a nonionic contrast agent (an index of microvascular permeability) before and after microembolization with microspheres at baseline and during adenosine infusion. A high-resolution three-dimensional microcomputed tomography (micro-CT) scanner was subsequently used to obtain ex vivo, the volume and corresponding surface area of the embolized myocardial islands within the perfusion territories of the microembolized coronary artery. EBCT-derived microvascular extraction of contrast agent increased within minutes after coronary microembolization (P < 0.001 vs. baseline and vs. control values). The increase in coronary microvascular permeability was highly correlated to the micro-CT-derived total surface area of the nonperfused myocardium (r = 0.83, P < 0.001). In conclusion, myocardial extravascular accumulation of contrast agent is markedly increased after coronary microembolization and its magnitude is in proportion to the surface area of the interface between the nonperfused and perfused territories.

Relating function to branching geometry: a micro-CT study of the hepatic artery, portal vein, and biliary tree

Utilizing micro-computed tomography images, the hierarchical structure, interbranch segment lengths and diameters of a hepatic artery, a portal vein, and two biliary trees from intact rat liver lobes were characterized. The data were investigated by analyzing the geometric properties of the vascular structures, such as how interbranch segment diameters change at bifurcation points. In the case of the hepatic artery and portal vein trees (in which the flow rate is high by comparison with that in the biliary tree), the vascular geometry is consistent with a fluid transport system which aims to simultaneously minimize both the power loss of laminar flow, and a cost function proportional to the total volume of material needed to maintain the system (lumenal contents). In comparison, the biliary tree (which has a low flow rate and an opposite flow direction to that of the hepatic artery and portal vein) was found to have a geometry in which the lumen cross-sectional area is maintained at bifurcations. These findings imply that the histological makeup and therefore the pathophysiology of biliary tree vasculature are likely very different from that of the vasculature within the systemic arterial tree. The extent to which the characteristic variability/scatter in the data may have resulted from imaging and/or measurement errors was examined by simulating such errors in a theoretical tree model and comparing the results with the measured data.

Direct three-dimensional coherently scattered x-ray microtomography

PURPOSE

It has been shown that coherently scattered x rays can be used to discriminate and identify specific components in a mixture of low atomic weight materials. The authors demonstrated a new method of doing coherently scattered x-ray tomography with a thin sheet of x ray.

METHODS

A collimated x-ray fan-beam, a parallel polycapillary collimator, and a phantom consisting of several biocompatible materials of low attenuation-based contrast were used to investigate the feasibility of the method. Because of the particular experimental setup, only the phantom translation perpendicular to the x-ray beam is needed and, thus, there is no need of Radon-type tomographic reconstruction, except for the correction of the attenuation to the primary and scattered x rays, which was performed by using a conventional attenuation-based tomographic image data set. The coherent scatter image contrast changes with momentum transfer among component materials in the specimen were investigated with multiple x-ray sources with narrow bandwidth spectra generated with anode and filter combinations of Cu/Ni (8 keV), Mo/Zr (18 keV), and Ag/Pd (22 keV) and at multiple scatter angles by orienting the detector and polycapillary collimator at different angles to the illuminating x ray.

RESULTS

The contrast among different materials changes with the x-ray source energy and the angle at which the image was measured. The coherent scatter profiles obtained from the coherent scatter images are consistent with the published results.

CONCLUSIONS

This method can be used to directly generate the three-dimensional coherent scatter images of small animal, biopsies, or other small objects with low atomic weight biological or similar synthetic materials with low attenuation contrast. With equipment optimized, submillimeter spatial resolution may be achieved.

Three-dimensional reconstruction of the human capillary network and the intramyocardial micronecrosis

Three-dimensional reconstruction of the human heart was performed to define the structure of the intramyocardial microvasculature. A total of 200 consecutive serial sections of 6 μm each were prepared from the left ventricular tissue of an autopsied human heart with normal coronary arteries. The corresponding arteriole, venule, and all capillaries were reconstructed using three-dimensional software. The capillary network extended right and left along the cardiomyocyte with major and minor axes of about 130 and 120 μm, respectively. The capillary length from an arteriole to an adjacent venule was about 350 μm. Two types of sack-like structures, the precapillary sinus and the capillary sinus, were present in the capillary network, and many capillaries diverged from these sinuses. The cardiomyocytes were covered with reticular capillaries. In contrast, the precapillary and capillary sinuses were surrounded by many cardiomyocytes. The arterial and venous capillaries were positioned alternately, forming a lattice pattern. Intramyocardial microcirculatory units forming a capillary network from an arteriole to adjacent venules on both sides were present. The sizes of myocardial micronecroses corresponded to that of the intramyocardial microcirculatory unit. These results show that the capillary network is an ordered and anatomically regulated structure and that the microcirculatory unit and the precapillary and capillary sinuses may play an important role in maintaining the intramyocardial microcirculation during contraction and relaxation.

Algorithm-enabled low-dose micro-CT imaging

Micro-computed tomography (micro-CT) is an important tool in biomedical research and preclinical applications that can provide visual inspection of and quantitative information about imaged small animals and biological samples such as vasculature specimens. Currently, micro-CT imaging uses projection data acquired at a large number (300-1000) of views, which can limit system throughput and potentially degrade image quality due to radiation-induced deformation or damage to the small animal or specimen. In this work, we have investigated low-dose micro-CT and its application to specimen imaging from substantially reduced projection data by using a recently developed algorithm, referred to as the adaptive-steepest-descent-projection-onto-convex-sets (ASD-POCS) algorithm, which reconstructs an image through minimizing the image total-variation and enforcing data constraints. To validate and evaluate the performance of the ASD-POCS algorithm, we carried out quantitative evaluation studies in a number of tasks of practical interest in imaging of specimens of real animal organs. The results show that the ASD-POCS algorithm can yield images with quality comparable to that obtained with existing algorithms, while using one-sixth to one quarter of the 361-view data currently used in typical micro-CT specimen imaging.

Automation of Hessian-Based Tubularity Measure Response Function in 3D Biomedical Images

The blood vessels and nerve trees consist of tubular objects interconnected into a complex tree- or web-like structure that has a range of structural scale 5 μm diameter capillaries to 3 cm aorta. This large-scale range presents two major problems; one is just making the measurements, and the other is the exponential increase of component numbers with decreasing scale. With the remarkable increase in the volume imaged by, and resolution of, modern day 3D imagers, it is almost impossible to make manual tracking of the complex multiscale parameters from those large image data sets. In addition, the manual tracking is quite subjective and unreliable. We propose a solution for automation of an adaptive nonsupervised system for tracking tubular objects based on multiscale framework and use of Hessian-based object shape detector incorporating National Library of Medicine Insight Segmentation and Registration Toolkit (ITK) image processing libraries.

Fine structure of breast tissue on micro computed tomography a feasibility study

RATIONALE AND OBJECTIVES

To evaluate the feasibility of micro computed tomography (CT) to assess the fine structure of breast tissue.

METHODS AND MATERIALS

Breast core needle biopsy specimens (0.8 to 1.2 mm diameter) from fifteen women with clustered microcalcifications were examined using micro CT with isotropic voxels of 8.4 μm. Reconstructed two- and three-dimensional images were compared with the corresponding histological slices. Gray-scale measurements were performed in adipose tissue, fibroglandular tissue, fibrous tissue, microcalcifications, and tumor. The Tukey-Kramer method was applied to test the statistically significant differences between gray-scale attenuation values of breast tissue components.

RESULTS

Soft-tissue architecture appearance at micro CT closely approximated that obtained by light microscopy at low power field. The Tukey-Kramer method revealed statistically significant differences for attenuation values for all combinations of breast tissue components with the exception of fibroglandular tissue versus fibrous tissue.

CONCLUSIONS

Micro CT is feasible for the differentiation of breast tissue components from core needle specimens.

Theoretical models for coronary vascular biomechanics: progress & challenges

A key aim of the cardiac Physiome Project is to develop theoretical models to simulate the functional behaviour of the heart under physiological and pathophysiological conditions. Heart function is critically dependent on the delivery of an adequate blood supply to the myocardium via the coronary vasculature. Key to this critical function of the coronary vasculature is system dynamics that emerge via the interactions of the numerous constituent components at a range of spatial and temporal scales. Here, we focus on several components for which theoretical approaches can be applied, including vascular structure and mechanics, blood flow and mass transport, flow regulation, angiogenesis and vascular remodelling, and vascular cellular mechanics. For each component, we summarise the current state of the art in model development, and discuss areas requiring further research. We highlight the major challenges associated with integrating the component models to develop a computational tool that can ultimately be used to simulate the responses of the coronary vascular system to changing demands and to diseases and therapies.