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Vasculature of the murine lower hind limb visualized by microCT. (A) Lateral 3D view of the hind limb vasculature. Voxel side length: 2.7 μ m. (B) Virtual transverse section of the vasculature (at the level indicated in A). Tibia (T) and fibula (F) appear lightly colored due to their high x-ray absorption. (C–F) Virtual transverse sections of isolated soleus (C,D) and plantaris (E,F) muscle, respectively. Voxel side length: 0.8 and 0.66 μ m respectively. (C'–F') Volumes of interest indicated by rectangles in (C–F), showing volume-rendered microvasculature at higher magnification with differing vessel densities, tortuosity and 3D arrangement.
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A detailed vascular visualization and adequate quantification is essential for the proper assessment of novel angiomodulating strategies. Here, we introduce an ex vivo micro-computed tomography (microCT)-based imaging approach for the 3D visualization of the entire vasculature down to the capillary level and rapid estimation of the vascular volume...
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... microvasculature of the murine hind limb visualized by microCT. In order to study the vascular network of the murine hind limb in 3D, a multi-scale imaging approach was followed. First, an overview scan of the contrast-enhanced vasculature was acquired (Fig. 3A,B). This enabled the visualization of all blood vessels 10 μ m in diameter or larger. The intravital injection of the solidifying contrast agent enabled an accurate visualization of the vasculature in situ and preserves the spatial relationship to other morpholog- ical structures, such as bones and nerves. Two muscles, soleus and ...
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... ical structures, such as bones and nerves. Two muscles, soleus and plantaris, known to exhibit different fiber type characteristics, were chosen to further characterize their microvascular architecture. Both muscles were scanned at higher resolution (voxel side length: 0.8 resp. 0.66 μ m) to detect all blood vessels including capil- laries ( Fig. 3C-F). Based on virtual transverse sections of the two muscles, equally sized volumes of interest were selected in order to study the vascular pattern in more detail (Fig. 3C'-F'). At higher magnification, the differences in vascular pattern between different muscles became more evident. In soleus muscles, capillaries appeared highly ...
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... their microvascular architecture. Both muscles were scanned at higher resolution (voxel side length: 0.8 resp. 0.66 μ m) to detect all blood vessels including capil- laries ( Fig. 3C-F). Based on virtual transverse sections of the two muscles, equally sized volumes of interest were selected in order to study the vascular pattern in more detail (Fig. 3C'-F'). At higher magnification, the differences in vascular pattern between different muscles became more evident. In soleus muscles, capillaries appeared highly tortuous and built a dense vascular network surrounding the muscle fibers ( Fig. 3C' ,D' and online video S2), whereas in plantaris muscles, capillaries appeared straighter, more ...
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... equally sized volumes of interest were selected in order to study the vascular pattern in more detail (Fig. 3C'-F'). At higher magnification, the differences in vascular pattern between different muscles became more evident. In soleus muscles, capillaries appeared highly tortuous and built a dense vascular network surrounding the muscle fibers ( Fig. 3C' ,D' and online video S2), whereas in plantaris muscles, capillaries appeared straighter, more sparsely arranged and less organized ( Fig. 3E' ...
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... the differences in vascular pattern between different muscles became more evident. In soleus muscles, capillaries appeared highly tortuous and built a dense vascular network surrounding the muscle fibers ( Fig. 3C' ,D' and online video S2), whereas in plantaris muscles, capillaries appeared straighter, more sparsely arranged and less organized ( Fig. 3E' ...
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... on the overview scans (voxel side length: 2.58 μ m), no significant vascular effects could be detected in any of the control hind limbs (Fig. 6A,D), whereas the three injection sites of VEGF-transduced myoblasts could be clearly identified and localized, and envelopes of densely arranged vessels could be seen surrounding each injec- tion site (Fig. 6D and online video ...
Citations
... The essential indices of skeletal muscle histochemical and morphologic phenotype, including fibre-type composition, fibre size, intramyocellular lipid content, capillary-to-fiber ratio and contractile properties, have all been shown to be altered in T1DM [15,[24][25][26], but considerable inconsistencies exist in findings and interpretations, probably due to methodological heterogeneity. In particular, capillarisation parameters are traditionally assessed with two-dimensional (2D) stereological methods, but it has been shown that this conventional approach is remarkably unreliable for quantifying the complex capillary network in skeletal muscles [27][28][29][30]. Specific indices such as structural anisotropy, orientation of linear structures, and topological properties can be more efficiently and 6 precisely quantified using three-dimensional (3D) analytic methods [27]. ...
Although the effect of type 1 diabetes (T1DM) on the histological phenotype of skeletal muscle, especially capillarisation, remains poorly understood, this study sought to elucidate the changes in skeletal muscle myosin heavy chain (MyHC) fibres and 3D capillary network characteristics in T1DM-induced mice. Female C57BL/6J-OlaHsd mice were categorized into streptozotocin (STZ)-induced diabetic (n = 12) and age-matched non-diabetic controls (n = 12). The muscle fibre phenotype of the soleus, gluteus maximus, and gastrocnemius muscles was determined by the expression of MyHC isoforms. In contrast, the capillaries of the gluteus maximus were assessed using immunofluorescence staining, confocal laser microscopy, and 3D image analysis. STZ-induced diabetic mice showcased elevated glucose levels, reduced body weight, and prolonged thermal latency, verifying the T1DM phenotype. In both T1DM and non-diabetic mice, the gluteus maximus and gastrocnemius muscles predominantly displayed fast-twitch type 2b fibres, with no significant differences noted. However, the soleus muscle in non-diabetic mice had a greater proportion of type 2a fibres and comparable type 1 fibre densities (26.2 ± 14.6 % vs. 21.9 ± 13.5 %) relative to diabetic mice. T1DM mice showed reduced fibre diameters (P = 0.026), and the 3D capillary network analysis indicated a higher capillary length per muscle volume in the gluteus maximus than controls (P < 0.05). T1DM instigated notable changes in skeletal muscle, such as MyHC fibre type shifts, diminished fibre diameters, and augmented relative capillarisation, potentially attributed to muscle fibre atrophy. Our results underscore the precision of the 3D analytical technique in delineating skeletal muscle capillary architecture and advise caution when interpreting 2D data for capillary changes in T1DM.
... It is practically the standard in the field to decalcify the bone samples to enable the proper visualization and segmentation of vasculature within bone tissue (Nunez et al., 2017, Roche et al., 2012. Based on published data (Schneider et al., 2009), we were successful in establishing a bone-decalcifying protocol (for murine hind limb) with 10% EDTA solution (Schaad et al., 2017). Such a decalcification step does not seem to negatively influence the bone structure as such but reduces the X-ray absorption of bone tissue and renders it impossible to visualize it simultaneously with the vasculature (Fig. 2). ...
... In most instances it leads to remarkably shorter scanning times. Furthermore, segmentation of the vasculature in the tomographic datasets becomes easier and a subsequent histological evaluation of the sample is facilitated by such a decalcification step (Schaad et al., 2017). ...
... The hereby described approach with µAngiofil provides more complete vascular filling (Hlushchuk et al., 2020, Leyssens et al., 2021 and is suitable for the visualization of the microvasculature within bone tissue with or without decalcification (Fig. 2). If a subsequent histological evaluation is desired, the developed decalcifying protocols enable correlative imaging of the same sample with preserved intravascular contrast agent (Schaad et al., 2017). Distinct differences in the attenuation between the µAngiofil and bone tissue allow for assessing vascularization and bone growth without the need to make two scans (before and after decalcification) and register them, saving labor, scanning time and without damaging the sample composition. ...
Angiogenesis is a physiological process essential for skeletal development and growth, for bone healing and regeneration. Various research areas, including implantology and tissue engineering, would benefit from improved three-dimensional (3D) imaging of the vasculature within bone tissue.
In the last decades, X-ray microtomography (microCT) has gained recognition as a non-destructive 3D imaging technique for bone morphology. The structural nature of skeletal tissue has rendered the direct 3D imaging of its vasculature extremely difficult. For the detection of the vessels, contrast or casting agents must be used. A major drawback of such an approach has been the limited contrast between the common perfusion agents and mineralized tissue, which makes their distinct segmentation problematic. The usually applied decalcification resolves this issue but makes simultaneous assessment of the intracortical bone microstructure and the vascular morphology impossible. Moreover, the problem of contrasting becomes compounded in the presence of a metal implant.
Herewith we introduce the micro Angiofil-enhanced microCT-based visualization of vasculature within bone tissue in various small and large animal models, with and without decalcification. This study documents simultaneous microvascular and bone imaging in murine tibia, murine bone metastatic model, pulp chamber, gingiva and periodontal ligaments. In a large animal model (minipig) we present the visualization and segmentation of different tissue types and vessels in the hemimandible containing several metal implants.
Herewith we provide for the first time a non-destructive 3D imaging approach of the vasculature within soft and hard tissues in the vicinity of metal implants in a large animal model.
... This is specifically reported in diseases such as laminitis, navicular disease, tendon lacerations and impaired wound healing. To advance the research regarding both pathomechanisms of as well as diagnostic and therapeutic approaches to these diseases, there is a need for high-resolution, 3D-visualization and quantification of the vasculature (3,4). Angiography of the equine distal limb is currently described using radiography (5,6), fluoroscopy (7,8), computed tomography (CT) (9)(10)(11), and magnetic resonance imaging (MRI) (12). ...
... The main vessels, i.e., medial and lateral digital veins (100%), terminal arch (100%), perforating branches (100%), and circumflex vessels (100%) were consistently visualized in all limbs, at all expected levels and in all phases. Smaller caliber vessels, especially the coronary arteries (77%) and the arterial branches of the ergot (77%), of the digital torus (80%), and of the distal phalanx (73% dorsal, 52% palmar), were not as readily identified in all limbs when This table lists the number of vessel cross-sections visualized at every level for each limb (1)(2)(3)(4)(5) and this for the arterial (art), venous (ven) and arterial-venous combined dynamic (dyn) phases. The number of expected vessel cross-sections (medial + lateral) for every level is reported below the respective levels in the first column. ...
In-depth understanding of pathophysiological processes occurring in the vasculature of the equine distal limb is of great importance to improve both diagnostic and therapeutic approaches to diseases. To gain further insights, a model allowing high-resolution 3D-visualization of the vasculature is necessary. This pilot study evaluated the feasibility of restoring vascular perfusion in frozen-thawed distal equine cadaver limbs without prior preparation using computer tomographic imaging (CT). Five frozen-thawed, radiographically normal forelimbs were perfused with a lipophilic contrast agent through the median artery and radial vein in three phases (arterial, venous, and arterial-venous combined (AVC) dynamic). For comparison, one additional limb was perfused with a hydrosoluble contrast agent. The CT-studies (16-slice MDCT, 140 kV, 200 mA, 2 mm slice thickness, 1 mm increment, pitch 0.688) were evaluated at 11 specified regions for visualization of the vasculature and presence of artifacts or anatomic variations. The protocol used in this study proved to be feasible and provided good visualization (93.1%) of vasculature with low rates of artifacts. During the different phases, vascular visualization was similar, but while filling defects decreased in the later phases, extravasation worsened in the 2 limbs where it was observed. Subjectively, the best quality of angiographic images was achieved during the AVC dynamic phase. Perfusion with hydrosoluble contrast resulted in significantly lower vascular visualization (74.0%) and higher artifact rates. This study shows that reperfusion of frozen-thawed equine distal limbs with a lipophilic contrast agent allows for high-quality 3D-visualization of the vasculature and may serve as a model for in situ vascular evaluation in the future.
... There have been recent reports of elegant tissue preparation and imaging approaches for microvascular applications in a range of preclinical models 5,7,9,10,[16][17][18] . However, many of these techniques are not suitable for multimodality imaging workflows (as summarized in Supplementary Table 1) as they require specialized sample preparation protocols 5,7,9,10,16 (for example, resin embedding, cell labeling, optical clearing, decalcification), involve tissue sectioning before imaging or both 7,13 . ...
... There have been recent reports of elegant tissue preparation and imaging approaches for microvascular applications in a range of preclinical models 5,7,9,10,[16][17][18] . However, many of these techniques are not suitable for multimodality imaging workflows (as summarized in Supplementary Table 1) as they require specialized sample preparation protocols 5,7,9,10,16 (for example, resin embedding, cell labeling, optical clearing, decalcification), involve tissue sectioning before imaging or both 7,13 . The use of unique or bespoke vascular tags and labels (discussed in detail below) often precludes the use of complementary imaging methods due to their deleterious effects on endogenous and exogenous tissue contrast, and tissue sectioning hampers subsequent 3D imaging and histopathological analyses. ...
Despite advances in imaging, image-based vascular systems biology has remained challenging because blood vessel data are often available only from a single modality or at a given spatial scale, and cross-modality data are difficult to integrate. Therefore, there is an exigent need for a multimodality pipeline that enables ex vivo vascular imaging with magnetic resonance imaging, computed tomography and optical microscopy of the same sample, while permitting imaging with complementary contrast mechanisms from the whole-organ to endothelial cell spatial scales. To achieve this, we developed ‘VascuViz’—an easy-to-use method for simultaneous three-dimensional imaging and visualization of the vascular microenvironment using magnetic resonance imaging, computed tomography and optical microscopy in the same intact, unsectioned tissue. The VascuViz workflow permits multimodal imaging with a single labeling step using commercial reagents and is compatible with diverse tissue types and protocols. VascuViz’s interdisciplinary utility in conjunction with new data visualization approaches opens up new vistas in image-based vascular systems biology. VascuViz represents a versatile workflow for multimodal imaging of the vasculature in ex vivo tissue samples across length and resolution scales, paving the way for improved and novel image-based vascular systems biology applications.
... Additionally, application of various stimuli including local ischaemia, temperature changes, and vasoactive agents such as acetylcholine, adenosine, serotonin, bradykinin, and sodium nitroprusside, can be used to study microvascular response. Histological assessment of skeletal muscle microvasculature is conventionally accomplished by two-dimensional (2D) analyses of tissue cross-sections [52,53], although recently, a three-dimensional (3D) analytic technique that overcomes the usual technical biases and inconsistencies associated with the traditional 2D approach has been proposed [54][55][56]. ...
Obesity is a worrisomely escalating public health problem globally and one of the leading causes of morbidity and mortality from noncommunicable diseases. The epidemiological link between obesity and a broad spectrum of cardiometabolic disorders has been well documented; however, the underlying pathophysiological mechanisms are only partially understood, and effective treatment options remain scarce. Given its critical role in glucose metabolism, skeletal muscle has increasingly become a focus of attention in understanding the mechanisms of impaired insulin function in obesity and the associated metabolic sequelae. We examined the current evidence on the relationship between microvascular dysfunction and insulin resistance in obesity. A growing body of evidence suggests an intimate and reciprocal relationship between skeletal muscle microvascular and glucometabolic physiology. The obesity phenotype is characterized by structural and functional changes in the skeletal muscle microcirculation which contribute to insulin dysfunction and disturbed glucose homeostasis. Several interconnected etiologic molecular mechanisms have been suggested, including endothelial dysfunction by several factors, extracellular matrix remodelling, and induction of oxidative stress and the immunoinflammatory phenotype. We further correlated currently available pharmacological agents that have deductive therapeutic relevance to the explored pathophysiological mechanisms, highlighting a potential clinical perspective in obesity treatment.
... For the μCT images, the ex vivo specimen preparation changes vessel proportions due to removing the effect of neural or chemical signals that cause either vessel constriction or dilation. Additional factors such as tissue swelling, perfusion pressure during contrast administration, and the effect of contrast curing and paraffin embedding will affect the vessel dimensions 40,41 . Moreover, a smaller isometric voxel size is necessary for a more precise vessel delimitation. ...
... During the renal vascular flushing, the rat was euthanized by decapitation. Directly after flushing, 3 ml of μAngiofil contrast agent and hardener mixed according to the manufacturer's guidelines (Fumedica AG, Muri, Switzerland) was infused at 1 ml/ min 26,40 . The infusion continued until the entire surface of the kidney was blue, and a considerable amount of contrast had left the renal vein. ...
Super-resolution ultrasound imaging (SRUS) enables in vivo microvascular imaging of deeper-lying tissues and organs, such as the kidneys or liver. The technique allows new insights into microvascular anatomy and physiology and the development of disease-related microvascular abnormalities. However, the microvascular anatomy is intricate and challenging to depict with the currently available imaging techniques, and validation of the microvascular structures of deeper-lying organs obtained with SRUS remains difficult. Our study aimed to directly compare the vascular anatomy in two in vivo 2D SRUS images of a Sprague–Dawley rat kidney with ex vivo μ CT of the same kidney. Co-registering the SRUS images to the μ CT volume revealed visually very similar vascular features of vessels ranging from ~ 100 to 1300 μm in diameter and illustrated a high level of vessel branching complexity captured in the 2D SRUS images. Additionally, it was shown that it is difficult to use μ CT data of a whole rat kidney specimen to validate the super-resolution capability of our ultrasound scans, i.e . , validating the actual microvasculature of the rat kidney. Lastly, by comparing the two imaging modalities, fundamental challenges for 2D SRUS were demonstrated, including the complexity of projecting a 3D vessel network into 2D. These challenges should be considered when interpreting clinical or preclinical SRUS data in future studies.
... Majority of the current data regarding capillary network changes in obesity and diabetes are based on 2D analyses of tissue cross-sections, with capillarisation being assessed by different indices, introducing additional variability and possible inconsistencies between studies (Montero 2016). There have been a few attempts to develop methods for evaluation of the capillary network of skeletal muscles from 3D data Schaad et al. 2017). However, most of these novel methods require in vivo perfusion of tissue with contrast agents, and are therefore not suitable to study capillary network in biopsy samples. ...
Background: Obesity-related metabolic disorders are among the leading causes of morbidity and mortality in the developed world. Structural and functional changes in skeletal muscles and the microvasculature are critically involved in the mediation of obesity-related insulin resistance. A shift from expression of slow to fast type myosin heavy chain isoforms in slow twitch muscles has been shown to contribute to reduced insulin sensitivity in obesity, while in fast-twitch weight-bearing muscles no fibre type shifting was observed. Furthermore, in obesity, accumulation of lipid droplets in skeletal muscle fibres can also contribute to insulin resistance. However, it is not yet clear how intramyocellular lipid accumulation and fibre type changes are associated. Moreover, in advanced obesity with insulin resistance, reduced capillary network density in skeletal muscles and impaired capillary recruitment has been demonstrated. On the other hand, in the early stage of obesity with insulin resistance, an increased functional vascular response to insulin has been described. However, it remains unclear whether such functional vascular response is associated with morphological alterations in the capillary network, or if the switch of fibre types toward fast type isoforms also occurs in fast-twitch, non-weight-bearing muscles in the early stages of obesity with insulin resistance.
Methods: The study was carried out using eighteen 54-week-old C57BL/6JOlaHsd mice, divided into two study groups of nine mice each: the high fat diet-induced obese and the standard diet-treated lean groups. Insulin resistance status was assessed by the oral glucose tolerance test and fasting glucose measurements. We determined the capillary network characteristics using 3D analysis of 100 µm thick transverse sections of gluteus maximus muscle, and employed immunofluorescent techniques to mark the capillary endothelium and the basement membrane of capillaries and muscle fibres, which were then captured with a confocal microscope and analysed with the Ellipse software. We used the indirect immunohistochemical method to determine the myosin heavy chain isoform expression in muscle fibres. Antibodies against myosin heavy chain isoforms type 1, 2a, 2x/d and 2b were used to determine the expression of individual myosin heavy chain isoforms in successive 10 µm thick sections of gluteus maximus, gastrocnemius, plantaris and soleus muscles. We performed analysis of intramyocellular lipid content using 10 µm thick sections of gastrocnemius, plantaris and soleus muscles stained with Sudan Black B, and calculated the lipid content index as 100 times the ratio of the cross-sectional area of muscle fibre occupied by lipid droplets to the cross-sectional area of muscle fibre. The deformations of skeletal muscle thick tissue sections in horizontal plane were determined by comparison of gluteus maximus muscle fibre diameters in 10 µm thick native tissue sections to 100 µm thick fixed and immunofluorescently labelled tissue sections, respectively.
Results: Compared to the standard diet-treated lean mice, mice fed on a high fat diet had a significantly increased body mass (p = 0.0001) and basal glycaemia, and decreased glucose tolerance (p < 0.05). The obese mice also showed denser capillary network of the gluteus maximus muscle compared to lean mice. Compared to the lean mice, capillary length per muscle fibre length, and capillary length per muscle fibre surface area were significantly larger around small muscle fibres (< 40 µm) (p < 0.05) in the obese mice, while there were no significant differences around large fibres in both groups. Other capillary characterization indices such as tortuosity, anisotropy and fibre diameter did not significantly differ between the study groups. In the slow-twitch soleus and fast-twitch non-weight-bearing gluteus maximus muscles, we noted a shift towards fast type myosin heavy chain isoform expression in the obese mice (p < 0.05), while in the weight-bearing fast-twitch gastrocnemius and intermediate plantaris muscles there were no significant differences in myosin heavy chain expression between the two study groups. Moreover, in obese mice muscle fibre size and intramyocellular lipid content were significantly increased in type 2a and 2x/d muscle fibres (p<0.05), with greater prominence in the fast- and intermediate-twitch than slow-twitch skeletal muscles. During the preparation of thick transverse sections of skeletal muscle for confocal microscopy, we demonstrated significant dilation of the sections in horizontal direction (p < 0.001) and shrinkage in the axial direction (p < 0.001). In addition, we noted a positive correlation between the magnitude of horizontal dilation and the magnitude of shrinkage in the axial direction (r = 0.493, p < 0.01), the latter being more pronounced in transversely than obliquely cut tissue sections.
Conclusions: We found a selective increase in capillarisation around small muscle fibres of the more oxidative fibre types in our obese insulin-resistant mice, which could be an early compensatory mechanism ameliorating obesity-related insulin resistance. Our findings further suggest that in obesity with insulin resistance, both slow- and fast-twitch muscles exhibit the tendency for a shift toward fast type myosin heavy chain isoforms, and that increased weight bearing may condition the resistance of fast-twitch muscles to fibre type shifting. Our results also reaffirm that in obesity, intramyocellular lipid accumulation is specific for both skeletal muscle and fibre types, with greater prominence in fast-twitch muscles and muscle fibre types 1, 2a and 2x/d. Finally, our study also provide evidence on horizontal dilation and axial shrinkage of thick transverse sections of skeletal muscle. The magnitude of the former was partially dependent on the latter, suggesting that even though axial shrinkage can be corrected by calibration, histological protocols should be optimised to minimize the axial collapse that could cause horizontal dilation.
... To visualize blood vessels, immunohistochemical techniques targeting endothelial markers such as cluster of differentiation (CD) 31 [11][12][13] or basement membrane markers such as laminin [14,15] have been widely used. More recently, methods including intravenous injection of fluorescent dyes followed by in vivo two-photon imaging [16][17][18][19] or intravenous injection of polymerizing contrast agents followed by ex vivo microCT [20] have been developed. ...
The vascular system is vital for all tissues and the interest in its visualization spans many fields. A number of different plant-derived lectins are used for detection of vasculature; however, studies performing direct comparison of the labeling efficacy of different lectins and techniques are lacking. In this study, we compared the labeling efficacy of three lectins: Griffonia simplicifolia isolectin B4 (IB4); wheat germ agglutinin (WGA), and Lycopersicon esculentum agglutinin (LEA). The LEA lectin was identified as being far superior to the IB4 and WGA lectins in histological labeling of blood vessels in brain sections. A similar signal-to-noise ratio was achieved with high concentrations of the WGA lectin injected during intracardial perfusion. Lectins were also suitable for labeling vasculature in other tissues, including spinal cord, dura mater, heart, skeletal muscle, kidney, and liver tissues. In uninjured tissues, the LEA lectin was as accurate as the Tie2–eGFP reporter mice and GLUT-1 immunohistochemistry for labeling the cerebral vasculature, validating its specificity and sensitivity. However, in pathological situations, e.g., in stroke, the sensitivity of the LEA lectin decreases dramatically, limiting its applicability in such studies. This work can be used for selecting the type of lectin and labeling method for various tissues.
... In biomedical research, micro-CT has been used in a wide range of scientific fields such as musculoskeletal, neurological, cardiorespiratory, gastrointestinal research, and longitudinal studies for treatment effects (e.g., [10][11][12][13][14][15][16][17]). In recent years, it has been used also in biological fields such as taxonomy, ecology, and developmental research (e.g., [18][19][20]). ...
Several imaging techniques are used in biological and biomedical studies. Micro-computed tomography (micro-CT) is a non-destructive imaging technique that allows the rapid digiti-sation of internal and external structures of a sample in three dimensions and with great resolution. In this review, the strengths and weaknesses of some common imaging techniques applied in biological and biomedical fields, such as optical microscopy, confocal laser scanning microscopy, and scanning electron microscopy, are presented and compared with the micro-CT technique through five use cases. Finally, the ability of micro-CT to create non-destructively 3D anatomical and morphological data in sub-micron resolution and the necessity to develop complementary methods with other imaging techniques, in order to overcome limitations caused by each technique, is emphasised.
... 101 Quantitative analyses of the microvascular network using microCT exhibit a broad distribution of vessel diameters skewed toward larger vessel diameters. 102 Consequently, efforts have been made to generalize IVIM analysis beyond one pseudo-diffusion component in the kidney, 103 liver, 104 and brain. 105 However, these multiexponential efforts have not yet been performed in skeletal muscle, possibly due to the limited sensitivity/SNR of the effect even when one component is considered. ...
Throughout the body, muscle structure and function can be interrogated using a variety of noninvasive magnetic resonance imaging (MRI) methods. Recently, intravoxel incoherent motion (IVIM) MRI has gained momentum as a method to evaluate components of blood flow and tissue diffusion simultaneously. Much of the prior research has focused on highly vascularized organs, including the brain, kidney, and liver. Unique aspects of skeletal muscle, including the relatively low perfusion at rest and large dynamic range of perfusion between resting and maximal hyperemic states, may influence the acquisition, postprocessing, and interpretation of IVIM data. Here, we introduce several of those unique features of skeletal muscle; review existing studies of IVIM in skeletal muscle at rest, in response to exercise, and in disease states; and consider possible confounds that should be addressed for muscle-specific evaluations. Most studies used segmented nonlinear least squares fitting with a b-value threshold of 200 sec/mm² to obtain IVIM parameters of perfusion fraction (f), pseudo-diffusion coefficient (D*), and diffusion coefficient (D). In healthy individuals, across all muscles, the average ± standard deviation of D was 1.46 ± 0.30 × 10⁻³ mm²/sec, D* was 29.7 ± 38.1 × 10⁻³ mm²/sec, and f was 11.1 ± 6.7%. Comparisons of reported IVIM parameters in muscles of the back, thigh, and leg of healthy individuals showed no significant difference between anatomic locations. Throughout the body, exercise elicited a positive change of all IVIM parameters. Future directions including advanced postprocessing models and potential sequence modifications are discussed.
Level of Evidence
2
Technical Efficacy
Stage 2
