Acute Rat Lung Injury: Feasibility of Assessment with Micro-CT

Three-Dimensional Whole-Organ Characterization of the Regional Alveolar Morphology in Normal Murine Lungs

Alveolar architecture plays a fundamental role in the processes of ventilation and perfusion in the lung. Alterations in the alveolar surface area and alveolar cavity volume constitute the pathophysiological basis of chronic respiratory diseases such as pulmonary emphysema. Previous studies based on micro-computed tomography (micro-CT) of lung samples have allowed the geometrical study of acinar units. However, our current knowledge is based on the study of a few tissue samples in random locations of the lung that do not give an account of the spatial distributions of the alveolar architecture in the whole lung. In this work, we combine micro-CT imaging and computational geometry algorithms to study the regional distribution of key morphological parameters throughout the whole lung. To this end, 3D whole-lung images of Sprague–Dawley rats are acquired using high-resolution micro-CT imaging and analyzed to estimate porosity, alveolar surface density, and surface-to-volume ratio. We assess the effect of current gold-standard dehydration methods in the preparation of lung samples and propose a fixation protocol that includes the application of a methanol-PBS solution before dehydration. Our results show that regional porosity, alveolar surface density, and surface-to-volume ratio have a uniform distribution in normal lungs, which do not seem to be affected by gravitational effects. We further show that sample fixation based on ethanol baths for dehydration introduces shrinking and affects the acinar architecture in the subpleural regions. In contrast, preparations based on the proposed dehydration protocol effectively preserve the alveolar morphology.

The biology of human hair greying

Hair greying (canities) is one of the earliest, most visible ageing-associated phenomena, whose modulation by genetic, psychoemotional, oxidative, senescence-associated, metabolic and nutritional factors has long attracted skin biologists, dermatologists, and industry. Greying is of profound psychological and commercial relevance in increasingly ageing populations. In addition, the onset and perpetuation of defective melanin production in the human anagen hair follicle pigmentary unit (HFPU) provides a superb model for interrogating the molecular mechanisms of ageing in a complex human mini-organ, and greying-associated defects in bulge melanocyte stem cells (MSCs) represent an intriguing system of neural crest-derived stem cell senescence. Here, we emphasize that human greying invariably begins with the gradual decline in melanogenesis, including reduced tyrosinase activity, defective melanosome transfer and apoptosis of HFPU melanocytes, and is thus a primary event of the anagen hair bulb, not the bulge. Eventually, the bulge MSC pool becomes depleted as well, at which stage greying becomes largely irreversible. There is still no universally accepted model of human hair greying, and the extent of genetic contributions to greying remains unclear. However, oxidative damage likely is a crucial driver of greying via its disruption of HFPU melanocyte survival, MSC maintenance, and of the enzymatic apparatus of melanogenesis itself. While neuroendocrine factors [e.g. alpha melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH), ß-endorphin, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH)], and micropthalmia-associated transcription factor (MITF) are well-known regulators of human hair follicle melanocytes and melanogenesis, how exactly these and other factors [e.g. thyroid hormones, hepatocyte growth factor (HGF), P-cadherin, peripheral clock activity] modulate greying requires more detailed study. Other important open questions include how HFPU melanocytes age intrinsically, how psychoemotional stress impacts this process, and how current insights into the gerontobiology of the human HFPU can best be translated into retardation or reversal of greying.

Knockdown of TFPI-Anchored Endothelial Cells Exacerbates Lipopolysaccharide-Induced Acute Lung Injury Via NF-κB Signaling Pathway

As activation of the coagulation system is both a consequence and contributor to acute lung injury (ALI), pulmonary coagulopathy has become a potential target for therapeutic intervention in ALI patients. We investigated the effects and possible mechanisms of endothelial cell (EC)-anchored tissue factor pathway inhibitor (TFPI) on lipopolysaccharide (LPS)-induced ALI in mice. To assess the effect of EC-anchored TFPI deletion on ALI indices, TFPI knockout (cKO) mice were generated. Mice were instilled by direct intratracheal injection LPS for the preparation of an ALI model. Evans blue dye (EBD) was injected intravenously 2 h prior to animal sacrifice (48 h post-LPS). Lungs were fixed for histopathology and the prepared tissue was homogenized or used to extract bronchoalveolar lavage fluid (BALF) or detect EBD concentration. TFPI knockdown mice with ALI were compared to wild-type (WT) mice with ALI to assess the effect of TFPI on endothelial barrier function and inflammation. TFPI deletion markedly exacerbated LPS histopathological changes in lung, and the LPS changes in protein, EBD extravasation, proinflammatory cytokines TNF-α, IL-1β, and IL-6 in BALF in lung. The number and infiltration of white blood cells (WBCs) from BALF and lung tissue of TFPI cKO mice with LPS-challenged ALI was increased compared to WT mice with LPS-challenged ALI. We also found further increased toll-like receptor 4 and nuclear factor kappa-light-chain-enhancer of activated B cells activation and additional expression of vascular cell adhesion molecule 1 and reduction of angiotensin converting enzyme 2 expression in TFPI cKO+LPS mice compared with WT+LPS mice. Endothelial-specific TFPI deficiency promoted LPS-induced pulmonary inflammation and endothelial barrier permeability possibly via toll-like receptor 4-mediated nuclear factor kappa-light-chain-enhancer of activated B cells signaling pathway activation.

The role of three-dimensionality and alveolar pressure in the distribution and amplification of alveolar stresses

Alveolar stresses are fundamental to enable the respiration process in mammalians and have recently gained increasing attention due to their mechanobiological role in the pathogenesis and development of respiratory diseases. Despite the fundamental physiological role of stresses in the alveolar wall, the determination of alveolar stresses remains challenging, and our current knowledge is largely drawn from 2D studies that idealize the alveolar septal wall as a spring or a planar continuum. Here we study the 3D stress distribution in alveolar walls of normal lungs by combining ex-vivo micro-computed tomography and 3D finite-element analysis. Our results show that alveolar walls are subject to a fully 3D state of stresses rather than to a pure axial stress state. To understand the contributions of the different components and deformation modes, we decompose the stress tensor field into hydrostatic and deviatoric components, which are associated with isotropic and distortional stresses, respectively. Stress concentrations arise in localized regions of the alveolar microstructure, with magnitudes that can be up to 27 times the applied alveolar pressure. Interestingly, we show that the stress amplification factor strongly depends on the level of alveolar pressure, i.e, stresses do not scale proportional to the applied alveolar pressure. In addition, we show that 2D techniques to assess alveolar stresses consistently overestimate the stress magnitude in alveolar walls, particularly for lungs under high transpulmonary pressure. These findings take particular relevance in the study of stress-induced remodeling of the emphysematous lung and in ventilator-induced lung injury, where the relation between transpulmonary pressure and alveolar wall stress is key to understand mechanotransduction processes in pneumocytes.

MRI and CT lung biomarkers: Towards an in vivo understanding of lung biomechanics

BACKGROUND

The biomechanical properties of the lung are necessarily dependent on its structure and function, both of which are complex and change over time and space. This makes in vivo evaluation of lung biomechanics and a deep understanding of lung biomarkers, very challenging. In patients and animal models of lung disease, in vivo evaluations of lung structure and function are typically made at the mouth and include spirometry, multiple-breath gas washout tests and the forced oscillation technique. These techniques, and the biomarkers they provide, incorporate the properties of the whole organ system including the parenchyma, large and small airways, mouth, diaphragm and intercostal muscles. Unfortunately, these well-established measurements mask regional differences, limiting their ability to probe the lung's gross and micro-biomechanical properties which vary widely throughout the organ and its subcompartments. Pulmonary imaging has the advantage in providing regional, non-invasive measurements of healthy and diseased lung, in vivo. Here we summarize well-established and emerging lung imaging tools and biomarkers and how they may be used to generate lung biomechanical measurements.

METHODS

We review well-established and emerging lung anatomical, microstructural and functional imaging biomarkers generated using synchrotron x-ray tomographic-microscopy (SRXTM), micro-x-ray computed-tomography (micro-CT), clinical CT as well as magnetic resonance imaging (MRI).

FINDINGS

Pulmonary imaging provides measurements of lung structure, function and biomechanics with high spatial and temporal resolution. Imaging biomarkers that reflect the biomechanical properties of the lung are now being validated to provide a deeper understanding of the lung that cannot be achieved using measurements made at the mouth.

Progressive Vascular Functional and Structural Damage in a Bronchopulmonary Dysplasia Model in Preterm Rabbits Exposed to Hyperoxia

Bronchopulmonary dysplasia (BPD) is caused by preterm neonatal lung injury and results in oxygen dependency and pulmonary hypertension. Current clinical management fails to reduce the incidence of BPD, which calls for novel therapies. Fetal rabbits have a lung development that mimics humans and can be used as a translational model to test novel treatment options. In preterm rabbits, exposure to hyperoxia leads to parenchymal changes, yet vascular damage has not been studied in this model. In this study we document the early functional and structural changes of the lung vasculature in preterm rabbits that are induced by hyperoxia after birth. Pulmonary artery Doppler measurements, micro-CT barium angiograms and media thickness of peripheral pulmonary arteries were affected after seven days of hyperoxia when compared to controls. The parenchyma was also affected both at the functional and structural level. Lung function testing showed higher tissue resistance and elastance, with a decreased lung compliance and lung capacity. Histologically hyperoxia leads to fewer and larger alveoli with thicker walls, less developed distal airways and more inflammation than normoxia. In conclusion, we show that the rabbit model develops pulmonary hypertension and developmental lung arrest after preterm lung injury, which parallel the early changes in human BPD. Thus it enables the testing of pharmaceutical agents that target the cardiovascular compartment of the lung for further translation towards the clinic.

Modern Imaging Technologies in Toxicologic Pathology: An Overview

Modern imaging technology, now utilized in most biomedical research areas (bioimaging), enables the detection and visualization of biological processes at various levels of the molecule, organelle, cell, tissue, organ and/or whole body. In toxicologic pathology, the impact of modern imaging technology is becoming apparent from digital histopathology to novel molecular imaging for in vivo studies. This overview summarizes recent progresses in digital microscopy imaging and newly developed digital slide techniques. Applications of virtual microscopy imaging are discussed and compared to traditional optical microscopy reading. New generation digital pathology approaches, including automatic slide inspection, digital slide databases and image management are briefly introduced. Commonly used in vivo preclinical imaging technologies are also summarized. While most of these new imaging techniques are still undergoing rapid development, it is important that toxicologic pathologists embrace and utilize these technologies as advances occur.

Melatonin alleviates acute lung injury through inhibiting the NLRP3 inflammasome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are clinically severe respiratory disorders, and there are currently no Food and Drug Administration-approved drug therapies. Melatonin is a well-known anti-inflammatory molecule, which has proven to be effective in ALI induced by many conditions. Emerging studies suggest that the NLRP3 inflammasome plays a critical role during ALI. How melatonin directly blocks activation of the NLRP3 inflammasome in ALI remains unclear. In this study, using an LPS-induced ALI mouse model, we found intratracheal (i.t.) administration of melatonin markedly reduced the pulmonary injury and decreased the infiltration of macrophages and neutrophils into lung. During ALI, the NLRP3 inflammasome is significantly activated with a large amount of IL-1β and the activated caspase-1 occurring in the lung. Melatonin inhibits the activation of the NLRP3 inflammasome by both suppressing the release of extracellular histones and directly blocking histone-induced NLRP3 inflammasome activation. Notably, i.t. route of melatonin administration opens a more efficient therapeutic approach for treating ALI.

Sonothrombolysis with BR38 Microbubbles Improves Microvascular Patency in a Rat Model of Stroke

Background

Early recanalization of large cerebral vessels in ischemic stroke is associated with improved clinical outcome, however persisting hypoperfusion leads to poor clinical recovery despite large vessel recanalization. Limited experimental sonothrombolysis studies have shown that addition of microbubbles during treatment can improve microvascular patency. We aimed to determine the effect of two different microbubble formulations on microvascular patency in a rat stroke model.

Methods

We tested BR38 and SonoVue® microbubble-enhanced sonothrombolysis in Wistar rats submitted to 90-minute filament occlusion of the middle cerebral artery. Rats were randomized to treatment (n = 6/group): control, rt-PA, or rt-PA+3-MHz ultrasound insonation with BR38 or SonoVue® at full or 1/3 dose. Treatment duration was 60 minutes, beginning after withdrawal of the filament, and sacrifice was immediately after treatment. Vascular volumes were evaluated with microcomputed tomography.

Results

Total vascular volume of the ipsilateral hemisphere was reduced in control and rt-PA groups (p<0.05), but was not significantly different from the contralateral hemisphere in all microbubble-treated groups (p>0.1).

Conclusions

Microbubble-enhanced sonothrombolysis improves microvascular patency. This effect is not dose- or microbubble formulation-dependent suggesting a class effect of microbubbles promoting microvascular reopening. This study demonstrates that microbubble-enhanced sonothrombolysis may be a therapeutic strategy for patients with persistent hypoperfusion of the ischemic territory.

Optical coherence tomography in respiratory science and medicine: from airways to alveoli

Optical coherence tomography is a rapidly maturing optical imaging technology, enabling study of the in vivo structure of lung tissue at a scale of tens of micrometers. It has been used to assess the layered structure of airway walls, quantify both airway lumen caliber and compliance, and image individual alveoli. This article provides an overview of the technology and reviews its capability to provide new insights into respiratory disease.

Serial micro-CT assessment of the therapeutic effects of rosiglitazone in a bleomycin-induced lung fibrosis mouse model

Objective

The aim of this study was to assess the therapeutic effects of rosiglitazone with serial micro-CT findings before and after rosiglitazone administration in a lung fibrosis mouse model induced with bleomycin.

Materials and Methods

We instilled the bleomycin solution directly into the trachea in twenty mice (female, C57BL/6 mice). After the instillation with bleomycin, mice were closely observed for 3 weeks and then all mice were scanned using micro-CT without sacrifice. At 3 weeks, the mice were treated with rosiglitazone on days 21 to 27 if they had abnormal CT findings (n = 9, 45%). For the mice treated with rosiglitazone, we performed micro-CT with mouse sacrifice 2 weeks after the rosiglitazone treatment completion. We assessed the abnormal CT findings (ground glass attenuation, consolidation, bronchiectasis, reticular opacity, and honeycombing) using a five-point scale at 3 and 6 weeks using Wilcoxon-signed ranked test. The micro-CT findings were correlated with the histopathologic results.

Results

One out of nine (11.1%) mice improved completely. In terms of consolidation, all mice (100%) showed marked decrease from 3.1 ± 1.4 at 3 weeks to 0.9 ± 0.9 at 6 weeks (p = 0.006). At 6 weeks, mild bronchiectasis (n = 6, 66.7%), mild reticular opacity (n = 7, 77.8%) and mild honeycomb patterns (n = 3, 33.3%) appeared.

Conclusion

A serial micro-CT enables the evaluation of drug effects in a lung fibrosis mouse model.

Validation of noninvasive morphological and diffusion imaging in mouse emphysema by micro-computed tomography and hyperpolarized (129)Xe magnetic resonance imaging

Animal disease models are pivotal in investigating the pathogenesis of emphysema and developing novel drugs, but the modalities to evaluate murine emphysema models have been of limited validity and sensitivity. In this study, we evaluated hyperpolarized (129)Xe magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) compared with traditional methods, such as plethysmography and histology. Elastase-treated mice and adiponectin knockout mice were used as murine emphysema models to evaluate these modalities. Three weeks after elastase administration, significant and heterogeneous emphysema was evaluated according to the mean linear intercept and plethysmography parameters. Notably, the distribution of low-density areas, as examined by micro-CT, correlated with the mean linear intercept and plethysmography parameters in whole lungs. These correlations were also observed in regional areas. Furthermore, we introduced hyperpolarized (129)Xe MRI, which can evaluate gas exchange between the alveoli and blood during spontaneous breathing. Parameters of gas exchange (fD) and alveolar size (Vs/Va) were significantly decreased in elastase-treated mice, and moderately correlated with the plethysmography parameters. Of importance, we could detect a decrease of the fD value in low-density areas with micro-CT, suggesting that gas exchange decreased in emphysematous lesions. Likewise, these parameters (fD and Vs/Va) were also decreased in adiponectin knockout mice, which exhibit emphysema with a homogeneous distribution. We demonstrated the feasibility of (129)Xe MRI and micro-CT in combination with traditional modalities. These noninvasive modalities provide complementary data that can be used for repeated estimations of regional gas exchange and lung morphology.

A Quantitative Study of Airway Changes on Micro-CT in a Mouse Asthma Model: Comparison With Histopathological Findings

Purpose

To evaluate airway changes in ovalbumin-induced asthmatic mice in terms of postmortem micro-CT images and pathological findings.

Methods

Asthma was induced in mice by intraperitoneal injection and nasal instillation of ovalbumin aluminium hydroxide into mice (experimental group, n=6), and another group of mice received intraperitoneal injection and nasal instillation of distilled phosphate-buffered saline (control group, n=6). Bronchial lumen area was measured in the main bronchial lumen of the distal third bronchial branch level (6 parts per each mouse) on axial scans of Micro-CT, using a Lucion's smart pen (semi-automated) and a curve pen (manual). Bronchial wall thickness was obtained in 4 sections (2 levels on either side) after the third bronchial branch by measuring the diameter which was perpendicular to the longitudinal axis of the main bronchus on curved Multi-planar reconstruction (MPR) images. Histologic slides were obtained from the lesion that was matched with its CT images, and bronchial wall thicknesses were determined.

Results

The mean bronchial lumen area was 0.196±0.072 mm² in the experimental group and 0.243±0.116 mm² in the control group; the difference was significant. Bronchial wall thickness on micro-CT images (mean, 0.119±0.01 vs. 0.108±0.013 mm) and in pathological specimens (mean, 0.066±0.011 vs. 0.041±0.009 mm) were thicker in the experimental group than in the control group; bronchial wall thickness on micro-CT images correlated well with pathological thickness (for the experimental group, r=0.712; for the control group, r=0.46). The thick bronchial wall in the experimental group demonstrated submucosal hypertrophy along with goblet cell hyperplasia and smooth muscle hyperplasia.

Conclusions

The results of this study suggest that asthma may induce thickening of bronchial wall and narrowing of the lumen area on micro-CT images and that these results may significantly correlate with pathological findings.

Static and dynamic imaging of alveoli using optical coherence tomography needle probes

Imaging of alveoli in situ has for the most part been infeasible due to the high resolution required to discern individual alveoli and limited access to alveoli beneath the lung surface. In this study, we present a novel technique to image alveoli using optical coherence tomography (OCT). We propose the use of OCT needle probes, where the distal imaging probe has been miniaturized and encased within a hypodermic needle (as small as 30-gauge, outer diameter 310 μm), allowing insertion deep within the lung tissue with minimal tissue distortion. Such probes enable imaging at a resolution of ∼12 μm within a three-dimensional cylindrical field of view with diameter ∼1.5 mm centered on the needle tip. The imaging technique is demonstrated on excised lungs from three different species: adult rats, fetal sheep, and adult pigs. OCT needle probes were used to image alveoli, small bronchioles, and blood vessels, and results were matched to histological sections. We also present the first dynamic OCT images acquired with an OCT needle probe, allowing tracking of individual alveoli during simulated cyclical lung inflation and deflation.

Ex vivo imaging of mouse brain using micro-CT with non-ionic iodinated contrast agent: a comparison with myelin staining

OBJECTIVE

We investigated the use of micro-CT with contrast agent for the non-invasive characterisation of fixed mouse brain tissue specimens as a means to differentiate between grey and white matter.

METHODS

Nine mice were divided into two groups for micro-CT (n=6) and myelin staining (n=3) experiments. Six mice underwent in vivo micro-CT and were then prepared for brain specimens by transcardiac perfusion with paraformaldehyde. The six mouse brains were soaked in two different concentrations of non-ionic iodinated contrast agents (60 and 150 mg ml(-1)). Immersion times used for each concentration of iodine were for 3, 7 and 14 days. Three-dimensional ex vivo micro-CT images were acquired with a resolution of 39 μm(3) to create isotropic images. The other three mice were stained for evaluation of the myelin structure.

RESULTS

Soaking the brains in non-ionic iodinated contrast agent resulted in clear differences in signal between the grey matter, the white matter and the ventricular spaces. The 150 mg ml(-1) contrast agent solution yielded images with better contrast-to-noise ratio (CNR) than 60 mg ml(-1) iodine contrast agent solution. 14 days of soaking yielded images with better CNR than 3 and 7 days. The CT contrast of grey and white matter derived from the iodine-soaked fixed brains was strongly related to tissue myelin.

CONCLUSION

The present study demonstrated that micro-CT can be used to detect the mouse brain myelin structure at 3, 7 and 14 days after fixation using a CT contrast agent.

Fetal hyperglycemia alters lung structural development in neonatal rat

Maternal diabetes is associated with increased risk for abnormal fetal organogenesis, but its effects on the developing lungs are still insufficiently known. To determine the effect of maternal hyperglycemia on postnatal lung development, we studied lung structural and cellular changes in newborn rats exposed to intrauterine hyperglycemia. We induced hyperglycemia in Sprague-Dawley rats with i.p. streptozotocin before pregnancy and allowed the hyperglycemic and control dams deliver at term. Lungs were obtained on postnatal day (d) 0, d7, and d14 and analyzed for lung weight and morphology, as well as cellular apoptosis (TUNEL staining) and proliferation (PCNA staining). Quantitative micro-CT analysis of the lung vasculature was additionally performed at d14. At birth, maternal hyperglycemia resulted in decreased relative lung weight, thinner alveolar septa and increased cellular apoptosis and proliferation, when compared to controls. At 1 and 2 weeks of age pulmonary cell apoptosis and alveolar chord length remained unchanged, but cell proliferation and number of secondary crests were increased in the hyperglycemia-exposed neonatal lungs in comparison with the controls. Density of small arterioles on histological examination and the structure of pulmonary arterial vasculature in micro-CT analysis of the neonatal lungs were not influenced by maternal hyperglycemia. Our results suggest, that maternal hyperglycemia is related to developmental structural alterations in postnatal rat lungs. These early changes may reflect aberrant maturational adaptation in response to the hyperglycemic fetal environment.

Histochemical analyses and quantum dot imaging of microvascular blood flow with pulmonary edema in living mouse lungs by "in vivo cryotechnique"

Light microscopic imaging of blood vessels and distribution of serum proteins is essential to analyze hemodynamics in living animal lungs under normal respiration or respiratory diseases. In this study, to demonstrate dynamically changing morphology and immunohistochemical images of their living states, "in vivo cryotechnique" (IVCT) combined with freeze-substitution fixation was applied to anesthetized mouse lungs. By hematoxylin-eosin staining, morphological features, such as shapes of alveolar septum and sizes of alveolar lumen, reflected their respiratory conditions in vivo, and alveolar capillaries were filled with variously shaped erythrocytes. Albumin was usually immunolocalized in the capillaries, which was confirmed by double-immunostaining for aquaporin-1 of endothelium. To capture accurate time-courses of blood flow in peripheral pulmonary alveoli, glutathione-coated quantum dots (QDs) were injected into right ventricles, and then IVCT was performed at different time-points after the QD injection. QDs were localized in most arterioles and some alveolar capillaries at 1 s, and later in venules at 2 s, reflecting a typical blood flow direction in vivo. Three-dimensional QD images of microvascular networks were reconstructed by confocal laser scanning microscopy. It was also applied to lungs of acute pulmonary hypertension mouse model. Erythrocytes were crammed in blood vessels, and some serum components leaked into alveolar lumens, as confirmed by mouse albumin immunostaining. Some separated collagen fibers and connecting elastic fibers were still detected in edematous tunica adventitia near terminal bronchioles. Thus, IVCT combined with histochemical approaches enabled us to capture native images of dynamically changing structures and microvascular hemodynamics of living mouse lungs.

Phenotypic characterization of skeletal abnormalities of Osteopotentia mutant mice by micro-CT: a descriptive approach with emphasis on reconstruction techniques

PURPOSE

The novel protein osteopotentia (Opt) has recently been described as an essential regulator of postnatal osteoblast maturation and might possibly be responsible for some of the rarer types of osteogenesis imperfecta. Our aim was the evaluation of micro CT for the qualitative morphological assessment of skeletal abnormalities of Osteopotentia-mutant mice in comparison to radiography and histology.

MATERIALS AND METHODS

Four homozygous mice with insertional mutations in the Opt gene and three wild-type controls were examined ex vivo using radiography and micro-CT. Two of the homozygous animals were evaluated histologically (trichrome reagent). For the micro-CT evaluation three-dimensional (3D) surface reconstructions and two-dimensional (2D) multiplanar reformations (MPRs) were applied.

RESULTS

The Opt-homozygous mice exhibited severe growth. The radiographic examinations showed osteopenia and fractures with hypertrophic callus formation and pseudarthroses of the forelimbs and ribs. Micro-CT confirmed these findings and was able to demonstrate additional fractures especially at smaller bones such as the metacarpals and phalanges. Additional characterization and superior delineation of cortices and fracture fragments was achieved by 2D MPRs. Histological correlation verified several of these imaging findings.

CONCLUSION

Micro-CT is able to screen Opt-mutant mice for osseous pathologies and furthermore characterize these anomalies. The modality seems superior to conventional radiography, but is not able to demonstrate cellular pathology. However, histology is destructive and more time- and material-consuming than micro-CT. Additional information may be gathered by 2D MPRs.

Whole animal imaging

Translational research plays a vital role in understanding the underlying pathophysiology of human diseases, and hence development of new diagnostic and therapeutic options for their management. After creating an animal disease model, pathophysiologic changes and effects of a therapeutic intervention on them are often evaluated on the animals using immunohistologic or imaging techniques. In contrast to the immunohistologic techniques, the imaging techniques are noninvasive and hence can be used to investigate the whole animal, oftentimes in a single exam which provides opportunities to perform longitudinal studies and dynamic imaging of the same subject, and hence minimizes the experimental variability, requirement for the number of animals, and the time to perform a given experiment. Whole animal imaging can be performed by a number of techniques including x-ray computed tomography, magnetic resonance imaging, ultrasound imaging, positron emission tomography, single photon emission computed tomography, fluorescence imaging, and bioluminescence imaging, among others. Individual imaging techniques provide different kinds of information regarding the structure, metabolism, and physiology of the animal. Each technique has its own strengths and weaknesses, and none serves every purpose of image acquisition from all regions of an animal. In this review, a broad overview of basic principles, available contrast mechanisms, applications, challenges, and future prospects of many imaging techniques employed for whole animal imaging is provided. Our main goal is to briefly describe the current state of art to researchers and advanced students with a strong background in the field of animal research.

Angioarchitectural changes in subacute cerebral venous thrombosis. A synchrotron-based micro- and nano-CT study

It is well known that recanalization of thrombosed cerebral sinuses occurs early but without marked influence on the long-term outcome and on final venous infarct volume on magnetic resonance imaging. To better understand the possible microvascular mechanisms behind these clinical observations, we evaluated the sequels of subacute superior sagittal sinus (SSS) thrombosis in rats using micro- and nano-CT imaging of the same specimen to provide large volume and high resolution CT image data respectively. SSS thrombosis was induced in 11 animals which were euthanized after 6h (n=4) or 6 weeks (n=7). Eight sham-operated rats served as controls. After infusion of contrast into the vasculature of the brains, these were isolated and scanned using micro-, nano-, and synchrotron-based micro-CT ((8 μm³), (900 nm)³, and (1.9 μm³) voxel sizes). The cross-sectional area of the superior sagittal sinus, microvessels and cortical veins were quantified. Tissue sections were stained against VEGF antigen. Immunohistochemistry was confirmed using quantitative rtPCR. SSS thrombosis led to a congestion of the bridging veins after 6h. After 6 weeks, a network of small vessels surrounding the occluded SSS was present with concurrent return towards the diameter of the draining bridging veins of controls. This microvascular network connected to cortical veins as demonstrated by nano- and synchrotron-based micro-CT. Also the volume fraction and number of cortical veins increased significantly. Immunohistochemistry in the region of the microsvascular network demonstrated a strong immunoreactivity against VEGF, confirmed by rtPCR. The sequel of subacute SSS thrombosis induced a network of microvessels ("venogenesis") draining the bridging veins. Also the volume fraction of cortical veins increased significantly.

Combined contrast-enhanced ultrasound and rt-PA treatment is safe and improves impaired microcirculation after reperfusion of middle cerebral artery occlusion

In monitoring of recanalization and in sonothrombolysis, contrast-enhanced ultrasound (CEUS) is applied in extended time protocols. As extended use may increase the probability of unwanted effects, careful safety evaluation is required. We investigated the safety profile and beneficial effects of CEUS in a reperfusion model. Wistar rats were subjected to filament occlusion of the right middle cerebral artery (MCA). Reperfusion was established after 90 minutes, followed by recombinant tissue-type plasminogen activator (rt-PA) treatment and randomization to additional CEUS (contrast agent: SonoVue; 60 minutes). Blinded outcome evaluation consisted of magnetic resonance imaging (MRI), neurologic assessment, and histology and, in separate experiments, quantitative 3D nano-computed tomography (CT) angiography (900 nm(3) voxel size). Nano-CT revealed severely compromised microcirculation in untreated animals after MCA reperfusion. The rt-PA partially improved hemispheric perfusion. Impairment was completely reversed in animals receiving rt-PA and CEUS. This combination was more effective than treatment with either CEUS without rt-PA or rt-PA and ultrasound or ultrasound alone. In MRI experiments, CEUS and rt-PA treatment resulted in a significantly reduced ischemic lesion volume and edema formation. No unwanted effects were detected on MRI, histology, and intracranial temperature assessment. This study shows that CEUS and rt-PA is safe in the situation of reperfusion and displays beneficial effects on the level of the microvasculature.

Evaluation of the middle cerebral artery occlusion techniques in the rat by in-vitro 3-dimensional micro- and nano computed tomography

Background

Animal models of focal cerebral ischemia are widely used in stroke research. The purpose of our study was to evaluate and compare the cerebral macro- and microvascular architecture of rats in two different models of permanent middle cerebral artery occlusion using an innovative quantitative micro- and nano-CT imaging technique.

Methods

4h of middle cerebral artery occlusion was performed in rats using the macrosphere method or the suture technique. After contrast perfusion, brains were isolated and scanned en-bloc using micro-CT (8 μm)³ or nano-CT at 500 nm³ voxel size to generate 3D images of the cerebral vasculature. The arterial vascular volume fraction and gray scale attenuation was determined and the significance of differences in measurements was tested with analysis of variance [ANOVA].

Results

Micro-CT provided quantitative information on vascular morphology. Micro- and nano-CT proved to visualize and differentiate vascular occlusion territories performed in both models of cerebral ischemia. The suture technique leads to a remarkable decrease in the intravascular volume fraction of the middle cerebral artery perfusion territory. Blocking the medial cerebral artery with macrospheres, the vascular volume fraction of the involved hemisphere decreased significantly (p < 0.001), independently of the number of macrospheres, and was comparable to the suture method. We established gray scale measurements by which focal cerebral ischemia could be radiographically categorized (p < 0.001). Nano-CT imaging demonstrates collateral perfusion related to different occluded vessel territories after macrosphere perfusion.

Conclusion

Micro- and Nano-CT imaging is feasible for analysis and differentiation of different models of focal cerebral ischemia in rats.

Micro-CT of corrosion casts for use in the computer-aided design of microvasculature

Two-dimensional micro-computed tomography (micro-CT) slices can be reconstructed into three-dimensional (3D) models that demonstrate capillary beds. This study focused on the acquisition of data necessary to create scaffolding that directly mimics the unique structural patterns of a microvascular tree system. The Microfil vascular contrasting method was compared to the Baston's methylmethacrylate corrosion casting (BMCC) method to determine which provided the most accurate and high-resolution results for 3D micro-CT reconstruction derived from the two-dimensional micro-CT slices of the capillary beds. It was determined that the BMCC, a method traditionally used in the scanning electron microscopic analysis of the microvasculature, was the best method for representing capillary lumina for micro-CT scanning. The removal of tissues from the BMCC cast resulted in samples that eliminated background material, thus increasing the X-ray contrast levels of the CT images. This provided for a more complete and more distinguishable high-resolution image of the represented capillary lumina. Images created with this BMCC method were reconstructed in a stereolithography file format as 3D mesh structure for later importing into computer-aided design (CAD) software. The resulting Bio-CAD, then, can be used to guide the more accurate fabrication of the microvascular scaffolding and then serve as the framework for tissue engineering of microvascular structures. Results from this study clearly indicated that the BMCC method is superior to the Microfil method for accurate and complete high-resolution imaging of capillary beds.

In vitro evaluation of the sinus sagittalis superior thrombosis model in the rat using 3D micro- and nanocomputed tomography

INTRODUCTION

Thrombosis of the cerebral veins and sinus are common causes of stroke. Animal models help us to understand the underlying pathophysiology of this condition. Therefore, the purpose of our study was to evaluate a well-established model for sinus sagittalis (SSS) thrombosis using micro- and nanocomputed tomography (CT) imaging.

METHODS

SSS thrombosis was performed in four rats. After contrast perfusion, brains were isolated and scanned using micro-CT at (8 microm)(3) voxel size to generate 3D images of the cerebral vasculature. For more detailed information on vascular perfusion territories, nano-CT imaging was performed to investigate the boundary layer of contrast-enhanced vessels and the occluded veins. The venous and arterial vascular volume fraction and gray scale measurements were obtained in the SSS thrombosis group and compared to controls. The significance of differences in vascular volume fraction and gray scale measurements was tested with analysis of variance. Results were complemented with histology.

RESULTS

Micro-CT proved to accurately visualize and differentiate vascular occlusion territories performed in the SSS thrombosis model. Moreover, 3D micro-CT provided quantitative information on arterial and venous vascular volume fraction. Micro-CT imaging enables a total 3D visualization of complications (ventricle rupture) in the SSS thrombosis model. We established gray scale measurements by which focal cerebral ischemia could be radiographically categorized (p < 0.001).

CONCLUSIONS

Using nano-CT, the interface of contrast-perfused and occluded veins can be visualized. Micro-CT is feasible for analysis and differentiation of perfusion territories in an animal model of focal cerebral ischemia.

Computer-aided design of microvasculature systems for use in vascular scaffold production

In vitro biomedical engineering of intact, functional vascular networks, which include capillary structures, is a prerequisite for adequate vascular scaffold production. Capillary structures are necessary since they provide the elements and compounds for the growth, function and maintenance of 3D tissue structures. Computer-aided modeling of stereolithographic (STL) micro-computer tomographic (micro-CT) 3D models is a technique that enables us to mimic the design of vascular tree systems containing capillary beds, found in tissues. In our first paper (Mondy et al 2009 Tissue Eng. at press), using micro-CT, we studied the possibility of using vascular tissues to produce data capable of aiding the design of vascular tree scaffolding, which would help in the reverse engineering of a complete vascular tree system including capillary bed structures. In this paper, we used STL models of large datasets of computer-aided design (CAD) data of vascular structures which contained capillary structures that mimic those in the dermal layers of rabbit skin. Using CAD software we created from 3D STL models a bio-CAD design for the development of capillary-containing vascular tree scaffolding for skin. This method is designed to enhance a variety of therapeutic protocols including, but not limited to, organ and tissue repair, systemic disease mediation and cell/tissue transplantation therapy. Our successful approach to in vitro vasculogenesis will allow the bioengineering of various other types of 3D tissue structures, and as such greatly expands the potential applications of biomedical engineering technology into the fields of biomedical research and medicine.

Airway remodeling in a mouse asthma model assessed by in-vivo respiratory-gated micro-computed tomography

The aim of our study was to evaluate the feasibility of non-invasive respiratory-gated micro-computed tomography (micro-CT) for assessment of airway remodelling in a mouse asthma model. Six female BALB/c mice were challenged intranasally with ovalbumin. A control group of six mice received saline inhalation. All mice underwent plethysmographic study and micro-CT. For each mouse, peribronchial attenuation values of 12 bronchi were measured, from which a peribronchial density index (PBDI) was computed. Mice were then sacrificed and lungs examined histologically. Final analysis involved 10 out of 12 mice. Agreement of measurements across observers and over time was very good (intraclass correlation coefficients: 0.94-0.98). There was a significant difference in PBDI between asthmatic and control mice (-210 vs. -338.9 HU, P = 0.008). PBDI values were correlated to bronchial muscle area (r = 0.72, P = 0.018). This study shows that respiratory-gated micro-CT may allow non-invasive monitoring of bronchial remodelling in asthmatic mice and evaluation of innovative treatment effects.

Phase contrast microradiography of mouse lung using synchrotron X-ray: correlation with optical microscopy

PURPOSE

The purpose of this study is to evaluate the feasibility of phase contrast X-ray microtomography and microradiography, using a polychromatic synchrotron X-ray, for analysis of the mouse lung microstructure.

MATERIALS AND METHODS

Normal mice were used for experiments. Some of the mouse lungs were prepared by the lung fixation-inflation method. The resulting sponge-like inflated lung samples were used for microtomography. The remaining mouse lungs were cut into 10 microm sections and were used for microradiography and optical microscopic correlation. The experiments on mouse lung samples were performed at the 7B2 beamline of the Pohang Light Source in Korea.

RESULTS

Phase contrast X-ray microtomography of inflated lung samples showed individual alveolar structure on 3-D reconstruction. Phase contrast microradiographs of thin lung samples showed microstructure of lung, such as alveoli and bronchioles, and were well correlated with optical microscopic images.

CONCLUSIONS

The results indicate that the phase contrast X-ray microtomography and microradiography using polychromatic synchrotron X-ray is feasible for evaluation of microstructure of the lung.

Three-dimensional measurement of alveolar airspace volumes in normal and emphysematous lungs using micro-CT

In pulmonary emphysema, the alveolar structure progressively breaks down via a three-dimensional (3D) process that leads to airspace enlargement. The characterization of such structural changes has, however, been based on measurements from two-dimensional (2D) tissue sections or estimates of 3D structure from 2D measurements. In this study, we developed a novel silver staining method for visualizing tissue structure in 3D using micro-computed tomographic (CT) imaging, which showed that at 30 cmH20 fixing pressure, the mean alveolar airspace volume increased from 0.12 nl in normal mice to 0.44 nl and 2.14 nl in emphysematous mice, respectively, at 7 and 14 days following elastase-induced injury. We also assessed tissue structure in 2D using laser scanning confocal microscopy. The mean of the equivalent diameters of the alveolar airspaces was lower in 2D compared with 3D, while its variance was higher in 2D than in 3D in all groups. However, statistical comparisons of alveolar airspace size from normal and emphysematous mice yielded similar results in 2D and 3D: compared with control, both the mean and variance of the equivalent diameters increased by 7 days after treatment. These indexes further increased from day 7 to day 14 following treatment. During the first 7 days following treatment, the relative change in SD increased at a much faster rate compared with the relative change in mean equivalent diameter. We conclude that quantifying heterogeneity in structure can provide new insight into the pathogenesis or progression of emphysema that is enhanced by improved sensitivity using 3D measurements.

Monte carlo simulation of an X-ray pixel beam microirradiation system

Monte Carlo simulations are used in the development of a nanotechnology-based multi-pixel beam array small animal microirradiation system. The microirradiation system uses carbon nanotube field emission technology to generate arrays of individually controllable X-ray pixel beams that electronically form irregular irradiation fields having intensity and temporal modulation without any mechanical motion. The microirradiation system, once developed, will be incorporated with the micro-CT system already developed that is based on the same nanotechnology to form an integrated image-guided and intensity-modulated microirradiation system for high-temporal-resolution small animal research. Prospective microirradiation designs were evaluated based on dosimetry calculated using EGSnrc-based Monte Carlo simulations. Design aspects studied included X-ray anode design, collimator design, and dosimetric considerations such as beam energy, dose rate, inhomogeneity correction, and the microirradiation treatment planning strategies. The dosimetric properties of beam energies between 80-400 kVp with varying filtration were studied, producing a pixel beam dose rate per current of 0.35-13 Gy per min per mA at the microirradiation isocenter. Using opposing multi-pixel-beam array pairs reduces the dose inhomogeneity between adjacent pixel beams to negligible levels near the isocenter and 20% near the mouse surface.

3D micro-CT imaging of the postmortem brain

Magnetic resonance microscopy (microMRI) is becoming an important tool for non-destructive analysis of fixed brain tissue. However, unlike MRI, X-ray computed tomography (CT) scans show little native soft tissue contrast. In this paper, we explored the use of contrast enhanced (brains immersion stained in iodinated CT contrast media) micro-CT (microCT) for high resolution 3D imaging of fixed normal and pathological brains, compared to microMRI and standard histopathology. An optimum iodine concentration of 0.27 M resulted in excellent contrast between gray and white matter in normal brain and a wide range of anatomical structures were identified. In glioma bearing mouse brains, there was clear deliniation of tumor margin which closely matched that seen on histopathology sections. microCT tumor volume was strongly correlated with histopathology volume. Our data suggests that microCT image contrast in the immersion-stained brains is related to axonal density and myelin content. Compared to traditional histopathology, our microCT approach is relatively rapid and less labor intensive. In addition, compared to microMRI, microCT is robust and requires much lower equipment and maintenance costs. For simple measurements, such as tumor volume and non-destructive postmortem brain screening, microCT may prove to be a valuable alternative to standard histopathology or microMRI.

Optimization of a retrospective technique for respiratory-gated high speed micro-CT of free-breathing rodents

The objective of this study was to develop a technique for dynamic respiratory imaging using retrospectively gated high-speed micro-CT imaging of free-breathing mice. Free-breathing C57Bl6 mice were scanned using a dynamic micro-CT scanner, comprising a flat-panel detector mounted on a slip-ring gantry. Projection images were acquired over ten complete gantry rotations in 50 s, while monitoring the respiratory motion in synchrony with projection-image acquisition. Projection images belonging to a selected respiratory phase were retrospectively identified and used for 3D reconstruction. The effect of using fewer gantry rotations--which influences both image quality and the ability to quantify respiratory function--was evaluated. Images reconstructed using unique projections from six or more gantry rotations produced acceptable images for quantitative analysis of lung volume, CT density, functional residual capacity and tidal volume. The functional residual capacity (0.15 +/- 0.03 mL) and tidal volumes (0.08 +/- 0.03 mL) measured in this study agree with previously reported measurements made using prospectively gated micro-CT and at higher resolution (150 microm versus 90 microm voxel spacing). Retrospectively gated micro-CT imaging of free-breathing mice enables quantitative dynamic measurement of morphological and functional parameters in the mouse models of respiratory disease, with scan times as short as 30 s, based on the acquisition of projection images over six gantry rotations.

In vivo characterization of lung morphology and function in anesthetized free-breathing mice using micro-computed tomography

Lung morphology and function in human subjects can be monitored with computed tomography (CT). Because many human respiratory diseases are routinely modeled in rodents, a means of monitoring the changes in the structure and function of the rodent lung is desired. High-resolution images of the rodent lung can be attained with specialized micro-CT equipment, which provides a means of monitoring rodent models of lung disease noninvasively with a clinically relevant method. Previous studies have shown respiratory-gated images of intubated and respirated mice. Although the image quality and resolution are sufficient in these studies to make quantitative measurements, these measurements of lung structure will depend on the settings of the ventilator and not on the respiratory mechanics of the individual animals. In addition, intubation and ventilation can have unnatural effects on the respiratory dynamics of the animal, because the airway pressure, tidal volume, and respiratory rate are selected by the operator. In these experiments, important information about the symptoms of the respiratory disease being studied may be missed because the respiration is forced to conform to the ventilator settings. In this study, we implement a method of respiratory-gated micro-CT for use with anesthetized free-breathing rodents. From the micro-CT images, quantitative analysis of the structure of the lungs of healthy unconscious mice was performed to obtain airway diameters, lung and airway volumes, and CT densities at end expiration and during inspiration. Because the animals were free breathing, we were able to calculate tidal volume (0.09 +/- 0.03 ml) and functional residual capacity (0.16 +/- 0.03 ml).

Interstitial lung disease?the new synergy between radiology and pathology

In the last 30 years, high-resolution computed tomography (HRCT) has been the major advance in diagnosis of diffuse parenchymal lung disease (DPLD). We review the diagnostic accuracy of HRCT and discuss how the gold standard in diagnosis of DPLD has shifted from histopathological diagnosis in isolation to a multidisciplinary approach. This latter process is now accepted as providing the highest levels of diagnostic accuracy in patients with DPLD and lung biopsy is primarily reserved for cases with atypical clinical or radiological presentations.

Quantitative Imaging of Microvascular Permeability in a Rat Model of Lipopolysaccharide-Induced Sepsis

OBJECTIVES

The aim of the present study was to evaluate the magnitude of endothelial defects by micro-computed tomography (CT) quantitation of contrast agent diffusion across the vascular endothelium in a rat model of vascular permeability caused by lipopolysaccharide (LPS)-induced sepsis.

MATERIALS AND METHODS

LPS was administered intraperitoneally (i.p.) at a dose of 10 mg/kg body weight in male Wistar rats (n = 18). Vascular leakage and vascular volume were quantified, by micro-CT and cryostatic micro-CT. The contrast agents used were Fenestra ( approximately 70-nm particle diameter), Microfil (large polymer), and iopamidol (Isovue, MW 777 Dalton).

RESULTS

Micro-CT revealed an increase in endothelial permeability as indicated by entry of contrast agent (Fenestra) into the extravascular space after LPS administration (P < 0.01). Endotoxin exposure also induced a decrease of vascular luminal volume in the myocardium, liver, kidney, and colonic wall determined by micro-CT (P < 0.01). Vascular leakage, expressed as the ratio of extravascular to intravascular gray scale intensity (IE/II) after injection of contrast agent, increased significantly in the myocardium, liver, kidney, and colonic wall (P < 0.001). The elimination of iopamidol from the intravascular compartment in LPS-challenged rats was decreased compared with control rats. The endothelial defect size was estimated to be >70 nm and <1 microm.

CONCLUSION

Contrast agents are useful to characterize vascular leakage and vascular volume fraction in an animal model of endotoxin priming.

Micro-computed tomography of the lungs and pulmonary-vascular system

Three-dimensional imaging of the intact lung and its vasculature is essential if the hierarchical and volumetric aspects of its structures and functions are to be quantitated. Although this is possible with clinical multislice helical CT scanners, the spatial resolution does not scale down adequately for small rodents for which cubic voxel dimensions of 50-100 microm are required. Micro-computed tomography (micro-CT) provides the necessary spatial resolution of 3D images of the intact thoracic contents. Micro-CT can provide higher resolution so that basic micro-architectural structures, such as alveoli, can be individually visualized and quantitated. Dynamic events, such as the respiratory and cardiac cycles, can be imaged at multiple time points throughout a representative cycle by coordinating the scan sequence (i.e., gating) to the cycle phase of a sequence of cycles. Fusion of the micro-CT image data with other image data, such as micro-SPECT or histology, can enhance the information content beyond the mainly structural information provided by micro-CT. Conventional attenuation-based X-ray imaging can involve significant X-ray exposures at high spatial resolutions, and this could affect the phenotype (e.g., via interstitial fibrosis) and genotype (e.g., via mutation), so its use in longitudinal studies using micro-CT may be limited in some cases. However, because of recent developments in which the phase shift or refraction of X-rays rather than attenuation is used, the X-ray exposure may be significantly reduced.