Magnetic Resonance Microimaging Research Articles

In-Situ Quantitative and Multiscale Structural Study of Starch-Based Biomaterials Immersed in Water.

The behavior upon immersion in water of two types of starchy materials of biomedical relevance, amorphous potato starch and glycerol-plasticized potato starch, is analyzed in depth. Synchrotron X-ray scattering, specifically wide-angle X-ray scattering (WAXS), and magnetic resonance microimaging (MRμI) are used as very precise and nondestructive quantitative methods to monitor water transfers and structure changes in the samples, with refined spatial and kinetics results. The ingress of water in the cylinder-shaped samples can be inferred from both techniques, and from this, a diffusion mechanism is deduced for each sample type. Qualitatively, scattering and imaging give comparable results: plasticized samples are shown to behave close to a Fickian diffusion case, amorphous samples close to a case II. WAXS results also provide an in-depth knowledge of the crystalline structures associated to each step of the water ingress, and these are in turn correlated to water diffusion. To refine these observations, a recrystallized starch sample is also analyzed via WAXS. This study gives better insight into the structure of a material with a huge biomedical potential (as implants, for example), and for such applications, the behavior upon immersion in water is particularly relevant.

A rapid micro-magnetic resonance imaging scanning for three-dimensional reconstruction of peripheral nerve fascicles.

The most common methods for three-dimensional reconstruction of peripheral nerve fascicles include histological and radiology techniques. Histological techniques have many drawbacks including an enormous manual workload and poor image registration. Micro-magnetic resonance imaging (Micro-MRI), an emerging radiology technique, has been used to report results in the brain, liver and tumor tissues. However, micro-MRI usage for obtaining intraneural structures has not been reported. The aim of this study was to present a new imaging method for three-dimensional reconstruction of peripheral nerve fascicles by 1T micro-MRI. Freshly harvested sciatic nerve samples from an amputated limb were divided into four groups. Two different scanning conditions (Mannerist Solution/GD-DTPA contrast agent, distilled water) were selected, and both T1 and T2 phases programmed for each scanning condition. Three clinical surgeons evaluated the quality of the images via a standardized scale. Moreover, to analyze deformation of the two-dimensional image, the nerve diameter and total area of the micro-MRI images were compared after hematoxylin-eosin staining. The results show that rapid micro-MRI imaging method can be used for three-dimensional reconstruction of the fascicle structure. Nerve sample immersed in contrast agent (Mannerist Solution/GD-DTPA) and scanned in the T1 phase was the best. Moreover, the nerve sample was scanned freshly and can be recycled for other procedures. MRI images show better stability and smaller deformation compared with histological images. In conclusion, micro-MRI provides a feasible and rapid method for three-dimensional reconstruction of peripheral nerve fascicles, which can clearly show the internal structure of the peripheral nerve.

Correlation of Glioma Proliferation and Hypoxia by Luciferase, Magnetic Resonance, and Positron Emission Tomography Imaging.

Gliomas are the most common type of primary, malignant brain tumor and significantly impact patients, who have a median survival of ~1year depending on mutational background. Novel imaging modalities such as luciferase bioluminescence, micro-magnetic resonance imaging (micro-MRI), micro-computerized tomography (micro-CT), and micro-positron emission tomography (micro-PET) have expanded the portfolio of tools available to study this disease. Hypoxia, a key oncogenic driver of glioma and mechanism of resistance, can be studied in vivo by the concomitant use of noninvasive MRI and PET imaging. We present a protocol involving stereotactic injection of syngenic F98 luciferase-expressing glioma cells generated by our laboratory into Fischer 344 rat brains and imaging using luciferase. In addition, 18-F-fludeoxyglucose, 18F-fluoromisonidazole, and 18F-fluorothymidine PET imaging are compared with quantified luciferase flux. These tools can potentially be used for assessing tumor growth characteristics, hypoxia, mutational effects, and treatment effects.

Modeling Substrate Utilization, Metabolite Production, and Uranium Immobilization in Shewanella oneidensis Biofilms

In this study, we developed a two-dimensional mathematical model to predict substrate utilization and metabolite production rates in Shewanella oneidensis MR-1 biofilm in the presence and absence of uranium (U). In our model, lactate and fumarate are used as the electron donor and the electron acceptor, respectively. The model includes the production of extracellular polymeric substances (EPS). The EPS bound to the cell surface and distributed in the biofilm were considered bound EPS (bEPS) and loosely associated EPS (laEPS), respectively. COMSOL® Multiphysics finite element analysis software was used to solve the model numerically (model file provided in the Supplementary Material). The input variables of the model were the lactate, fumarate, cell and EPS concentrations, half saturation constant for fumarate, and diffusion coefficients of the substrates and metabolites. To estimate unknown parameters and calibrate the model, we used a custom designed biofilm reactor placed inside a nuclear magnetic resonance (NMR) microimaging and spectroscopy system and measured substrate utilization and metabolite production rates. From these data we estimated the yield coefficients, maximum substrate utilization rate, half saturation constant for lactate, stoichiometric ratio of fumarate and acetate to lactate and stoichiometric ratio of succinate to fumarate. These parameters are critical to predicting the activity of biofilms and are not available in the literature. Lastly, the model was used to predict uranium immobilization in S. oneidensis MR-1 biofilms by considering reduction and adsorption processes in the cells and in the EPS. We found that the majority of immobilization was due to cells, and that EPS was less efficient at immobilizing U. Furthermore, most of the immobilization occurred within the top 10 μm of the biofilm. To the best of our knowledge, this research is one of the first biofilm immobilization mathematical models based on experimental observation. It has the ability to predict the relative contributions to U immobilization of laEPS, bEPS, and cells.

Magnetic resonance microimaging of cancer cell spheroid constructs

Background:Hydrogel-based cell cultures are excellent tools for studying physiological events occurring in the growth and proliferation of cells, including cancer cells. Diffusion magnetic resonance is a physical technique that has been widely used for the characterisation of biological systems as well as hydrogels. In this work, we applied diffusion magnetic resonance imaging (MRI) to hydrogel-based cultures of human ovarian cancer cells. Methods:Diffusion-weighted spin-echo MRI measurements were used to obtain spatially-resolved maps of apparent diffusivities for hydrogel samples with different compositions, cell loads and drug (Taxol) treatment regimes. The samples were then characterised using their diffusivity histograms, mean diffusivities and the respective standard deviations, and pairwise Mann–Whitney tests. The elastic moduli of the samples were determined using mechanical compression testing. Results:The mean apparent diffusivity of the hydrogels was sensitive to the polymer content, cell load and Taxol treatment. For a given sample composition, the mean apparent diffusivity and the elastic modulus of the hydrogels exhibited a negative correlation. Conclusions:Diffusivity of hydrogel-based cancer cell culture constructs is sensitive to both cell proliferation and Taxol treatment. This suggests that diffusion-weighted imaging is a promising technique for non-invasive monitoring of cancer cell growth in hydrogel-based, cellularly-sparse 3D cell cultures. The negative correlation between mean apparent diffusivity and elastic modulus suggests that the diffusion coefficient is indicative of the average density of the physical microenvironment within the hydrogel construct.

Micro-MREによるゼラチンゲルとブタ肝臓の動的粘弾性計測

This study aimed to measure a viscoelastic property of gelatin gels and porcine liver by the magnetic resonance elastography using micro-magnetic resonance imaging (micro-MRE). In the experiments, gelatin gel specimens (90 × 70 × 50 mm) made of gelatin solution with 5, 7, 10, 12, and 15 wt% concentration were examined under excitation with longitudinal waves in frequency of 50-250 Hz and amplitude of 0.5 mm. The viscoelastic modulus was obtained as storage shear modulus G’ and loss shear modulus G”. As a result, G’ values increased with the concentration and the excitation frequency. G” value was much smaller than G’. Double-layer specimens composed of 5 and 15 wt% gelatin gels were also examined. The average of G’ in each concentration gel in the double-layer specimens showed no significant difference from the single-material specimens with the same concentration. Furthermore, a porcine liver specimen (150 × 50 × 30 mm) were examined; however, the specimen were not vibrated and the displacement distribution in the specimen was not observed. When porcine liver specimens were embedded in the 15 wt% gel (70 × 70 × 50 mm), the specimens were vibrated deeply and G’ and G” of the liver and gel regions were obtained. As a result, G’ of the gel region was almost the same as the value of the gel specimens. G’ of the liver region increased with the excitation frequency as well as the gel specimens. The viscoelastic modulus of the porcine liver could be measured by embedding it inside gelatin gel using the micro-MRE system. This study demonstrated the application of the MRE system as the dynamic viscoelasticity measurements of gelatin gel and liver specimen.

In situ nuclear magnetic resonance microimaging of live biofilms in a microchannel.

Biofilms are comprised of microbial cells and an extracellular polymeric substance (EPS) matrix that supports interactions between community members and with the local environment. The highly hydrated EPS matrix makes the application of many biofilm visualization techniques difficult. Hence, to better visualize how biofilms interact with their environment, there is a need for imaging techniques to monitor hydrated state biofilm dynamics. We employed an in situ dynamic approach to construct label-free images of biofilms. In situ imaging was conducted using a vacuum compatible microfluidic reactor, SALVI (System for Analysis at the Liquid Vacuum Interface), for biofilm growth; real-time confocal laser scanning microscopy analysis; and nuclear magnetic resonance (NMR) microimaging and spectroscopy. We integrated SALVI microchannel fluids and live biofilms to demonstrate in situ measurement capabilities, including velocity mapping, diffusion coefficient mapping, relaxometry, localized spectroscopy, relaxation times, porosity, and two- and three-dimensional imaging within the microchannel at high spatial resolution. We monitored organic acids adjacent to biofilms, suggesting that kinetic rate and substrate-product yield ratio studies are possible using the SALVI microfluidic reactor for growth characterizations. The integration of NMR microimaging studies into the SALVI platform demonstrates that a multimodal microfluidic platform can serve as an avenue to explore complex biological phenomena, such as biofilm attachment to surfaces, with detailed quantitative physical and chemical mapping. The further incorporation of other SALVI-compatible technologies, such as liquid time-of-flight secondary ion mass spectrometry imaging, with NMR microimaging will produce a powerful correlative approach to monitor in situ biofilm chemistry and dynamics at different spatial scales.

μ-ViP: Customized virtual phantom for quantitative magnetic resonance micro-imaging at high magnetic field

The applications of Magnetic Resonance micro-Imaging (MRμI) cover nowadays a wide range of fields. However few of them present quantitative measurements when the sample of interest changes over time or in case of a long acquisition time. In this domain, two challenges have to be overcome: the introduction of a phantom as a reference signal and the guarantee that this signal is stable over the experiment duration while some conditions such as temperature and/or the moisture are varied. The aim of the present study was to implement a dedicated experimental set-up to generate a virtual phantom (ViP) signal in a vertical-bore 11.7 T NMR spectrometer, equipped with a micro-imaging probe. This study shows that the generation of a micro-imaging-dedicated ViP (μ-ViP) signal is of great benefit for on-line quality control of the spectrometer performance during acquisition in the case of real-time experiments. Thus, μViP represents a step towards improvement of the magnetic resonance signal quantification in small samples.

Multiparametric Classification of Skin from Osteogenesis Imperfecta Patients and Controls by Quantitative Magnetic Resonance Microimaging.

The purpose of this study is to evaluate the ability of quantitative magnetic resonance imaging (MRI) to discriminate between skin biopsies from individuals with osteogenesis imperfecta (OI) and skin biopsies from individuals without OI. Skin biopsies from nine controls (unaffected) and nine OI patients were imaged to generate maps of five separate MR parameters, T1, T2, km, MTR and ADC. Parameter values were calculated over the dermal region and used for univariate and multiparametric classification analysis. A substantial degree of overlap of individual MR parameters was observed between control and OI groups, which limited the sensitivity and specificity of univariate classification. Classification accuracies ranging between 39% and 67% were found depending on the variable of investigation, with T2 yielding the best accuracy of 67%. When several MR parameters were considered simultaneously in a multivariate analysis, the classification accuracies improved up to 89% for specific combinations, including the combination of T2 and km. These results indicate that multiparametric classification by quantitative MRI is able to detect differences between the skin of OI patients and of unaffected individuals, which motivates further study of quantitative MRI for the clinical diagnosis of OI.

Free water in bean seeds: The imbibition process observed by micro-magnetic resonance imaging

Water uptake by dry Lima beans (Phaseolus limensis L.) was traced using 1H micro-magnetic resonance imaging. The studies are performed using two-dimensional longitudinal images. Channels through which water comes in an imbibing bean seed are determined; the water distribution inside the seed is shown to be heterogeneous.

A Multidisciplinary Assessment of Remote Myocardial Fibrosis After Reperfused Myocardial Infarction in Swine and Patients.

In extensive nonreperfused myocardial infarction (MI), remote fibrosis has been documented. Early reperfusion by primary angioplasty represents the gold standard method to minimize the extension of the infarction. We aimed to ascertain whether fibrosis also affects remote regions in reperfused MI in swine and patients. Swine were subjected to a transient occlusion of the left anterior descending artery followed by 1-week or 1-month reperfusion. Collagen content in the remote area macroscopically, microscopically, by magnetic resonance microimaging, and at the molecular level was similar to controls. In patients with previous MI, samples from autopsies displayed a significant increase in collagen content only in the infarct region. In patients with previous MI submitted to cardiac magnetic resonance-T1 mapping, the extracellular volume fraction in remote segments was similar to that for controls. In all scenarios, the remote region did not show a significant increase of collagen content in comparison with controls.

Optical coherence tomography for embryonic imaging: a review.

Embryogenesis is a highly complex and dynamic process, and its visualization is crucial for understanding basic physiological processes during development and for identifying and assessing possible defects, malformations, and diseases. While traditional imaging modalities, such as ultrasound biomicroscopy, micro-magnetic resonance imaging, and micro-computed tomography, have long been adapted for embryonic imaging, these techniques generally have limitations in their speed, spatial resolution, and contrast to capture processes such as cardiodynamics during embryogenesis. Optical coherence tomography (OCT) is a noninvasive imaging modality with micrometer-scale spatial resolution and imaging depth up to a few millimeters in tissue. OCT has bridged the gap between ultrahigh resolution imaging techniques with limited imaging depth like confocal microscopy and modalities, such as ultrasound sonography, which have deeper penetration but poorer spatial resolution. Moreover, the noninvasive nature of OCT has enabled live imaging of embryos without any external contrast agents. We review how OCT has been utilized to study developing embryos and also discuss advances in techniques used in conjunction with OCT to understand embryonic development.

Water entry for the black locust (Robinia pseudoacacia L.) seeds observed by dedicated micro-magnetic resonance imaging.

Water entry at germination for black locust (Robinia pseudoacacia L.) seeds which are known as hard seeds with impermeable seed coat to water, was examined using micro-magnetic resonance imaging (MRI). The MRI apparatus equipped with a low-field (1 T; Tesla) permanent magnet was used, which is open access, easy maintenance, operable and transportable. The excellent point of the apparatus is that T 1-enhancement of water signals absorbed in dry seeds against steeping free water is stronger than the apparatuses with high-field superconducting magnets, which enabled clear detection of water entry. Water hardly penetrated into the seeds for more than 8h but approximately 60% of seeds germinated by incubating on wet filter papers for several days. Hot water treatments above 75°C for 3min effectively induced water gap; scarification was 70% at 100°C and 75°C, declined to 15% at 50°C and decreased further at room temperature. Water entered into the scarified seeds exclusively through the lens, spread along the dorsal side of the seeds and reached the hypocotyl, whereas water migrated slowly through hilum side to radicle within 3h.

Differences in perilymphatic space enhancement and adverse inflammatory reaction after intratympanic injection of two different gadolinium agents: A 9.4-T magnetic resonance imaging study

PurposeTo compare the inner ear enhancement after intratympanic injection of two widely used gadolinium (Gd) agents by 9.4 T micro-magnetic resonance imaging (MRI) and to investigate the effects of Gd on the inner ear. MethodsTwelve ears of six rats received intratympanic administration of 1/5 diluted Gd agents: gadoterate meglumine (Gd-DTPA) for the left ear and gadodiamide (Gd-DTPA-BMA) for the right ear. MRI was performed every 30 min from 1 to 4 h after administration. The normalized signal intensity was evaluated by quantitative analysis at each cochlear fluid compartment. Eight, six, and seven ears treated with Gd-DTPA, Gd-DPTA-BMA, and nothing as controls, respectively, were processed for histological evaluation after MRI. After hematoxylin & eosin staining, adverse inflammatory reactions were evaluated for turbid aggregation and lymphocytes. ResultsThe perilymphatic enhancement of Gd-DTPA was superior to that of Gd-DTPA-BMA regardless of cochlear turn, compartment, and time point. Inflammatory reactions were found in 4/8 (50.0%) and 4/6 (66.6%) ears administered Gd-DTPA and Gd-DTPA-BMA, respectively. Regardless of the contrast agent used, inflammatory reactions were most definite in the scala tympani of the basal turn, i.e., near the round window. Slightly greater inflammatory reactions were observed in ears injected with Gd-DTPA-BMA compared to Gd-DTPA although the difference was not statistically significant. No inflammatory reaction was observed in any of the seven controls. The auditory brainstem response threshold was 11.8 ± 2.5 dB SPL before IT Gd injection and it did not change for up to 5 days (15.4 ± 6.6 dB SPL) post-injection. ConclusionsGd-DTPA was superior to Gd-DTPA-BMA for visualization of the inner ear. Administration of diluted Gd agents intratympanically may induce considerable inflammatory reactions in the inner ear.

Magnetic resonance microimaging of a swine infarcted heart: Performing cardiac virtual histologies.

The aim of this study is to develop a computer-aided intuitive software tool based on MATLAB to reproduce the functions of a virtual histology over Magnetic Resonance (MR) microimages of small samples of swine's infarcted hearts. The basic characterization consists of selecting regions of interest (ROIs) of that MR microimage and extracting the most important information of these regions. The software tool will implement intuitive and sophisticated tools that allow the user to define ROIs on the different types of images provided by the MR scanner. The final purpose of this tool will be to analyze the acquired data in order to characterize some aspects of the later possible events after a myocardial infarction in swine's hearts and expand the study to human cases.

Distribution of the equilibrium moisture content in four hardwoods below fiber saturation point with magnetic resonance microimaging

The distribution of liquid and bound water in wood samples under equilibrium moisture contents (EMC) below fiber saturation point (FSP) was assessed by magnetic resonance (MR) microimaging. Two Amazonian hardwoods, huayruro (Robinia coccinea) and cachimbo [Cariniana domesticata], a plantation grown eucalyptus (Eucalyptus saligna), and a temperate species red oak (Quercus rubra) were studied. Desorption tests were performed at 21 °C from full saturation state for huayruro, cachimbo, and red oak, and from green condition for eucalyptus. The EMC was reached under three desorption conditions [58, 76, and 90 % relative humidity (RH)]. MR microimages were obtained based on T 2 times and on 1H concentration. Scanning electron microscopy images helped us to interpret MR microimages. The results showed that wood structure plays a major role in liquid water drainage and in water diffusion. Eucalyptus saligna and red oak showed liquid water entrapped in parenchyma tissues, even below FSP (90 % RH). At this same RH level, all liquid water was, however, drained for cachimbo and huayruro. For these woods, bound water was not uniformly distributed in wood structure, concentrating it more in fibers for both species. Huayruro showed the highest heterogeneity in hygroscopicity, which is explained by its particular wood anatomy.

Development of an Experimental Drug Eluting Suprachoroidal Microstent as Glaucoma Drainage Device.

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes. Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC). Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology. In vitro, faster drug release from both polymers was observed for MitC compared to PTX. Comparing polymers, the release from P(3HB) matrix was slower for both drugs. MRI and OCT showed all implants maintained a proper location. An effective IOP reduction was observed for up to 6 weeks in eyes with microstents combined with a drug-releasing LDD system. Overall, the surrounding tissue revealed mild-to-moderate inflammation. No pronounced fibrosis was observed in any of the groups. However, both drugs caused damage to the neighboring retina. The suprachoroidal microstent reduced IOP with mild inflammation in rabbit eyes. To avoid negative effects on the retina, it is necessary to identify novel drugs with less cytotoxicity. Future studies are needed to explore the fibrotic process over the long-term. The presented data serve as a proof of principle study for the concept of a suprachoroidal drug eluting microstent. Future device improvements will be focused on the design of LDD systems and the use of specific anti-inflammatory or antifibrotic agents with less cytotoxicity compared to MitC or PTX. Long-term animal studies using a reliable glaucoma model will be a further step towards clinical application and improvement of surgical glaucoma therapy.

3D mapping of neuronal migration in the embryonic mouse brain with magnetic resonance microimaging

A prominent feature of the developing mammalian brain is the widespread migration of neural progenitor (NP) cells during embryogenesis. A striking example is provided by NP cells born in the ventral forebrain of mid-gestation stage mice, which subsequently migrate long distances to their final positions in the cortex and olfactory bulb. Previous studies have used two-dimensional histological methods, making it difficult to analyze three-dimensional (3D) migration patterns. Unlike histology, magnetic resonance microimaging (micro-MRI) is a non-destructive, quantitative and inherently 3D imaging method for analyzing mouse embryos. To allow mapping of migrating NP cells with micro-MRI, cells were labeled in situ in the medial (MGE) and lateral (LGE) ganglionic eminences, using targeted in utero ultrasound-guided injection of micron-sized particles of iron-oxide (MPIO). Ex vivo micro-MRI and histology were then performed 5–6days after injection, demonstrating that the MPIO had magnetically labeled the migrating NP populations, which enabled 3D visualization and automated segmentation of the labeled cells. This approach was used to analyze the distinct patterns of migration from the MGE and LGE, and to construct rostral–caudal migration maps from each progenitor region. Furthermore, abnormal migratory phenotypes were observed in Nkx2.1−/− embryos, most notably a significant increase in cortical neurons derived from the Nkx2.1−/− LGE. Taken together, these results demonstrate that MPIO labeling and micro-MRI provide an efficient and powerful approach for analyzing 3D cell migration patterns in the normal and mutant mouse embryonic brain.

Experimental system to detect a labeled cell monolayer in a microfluidic environment.

To investigate the feasibility of detecting a living cell monolayer labeled with gadoterate (Gd-DOTA) in a microfluidic environment, by micromagnetic resonance imaging (MRI) in a 2.35T small-animal system. The development of new targeted contrast agents (CAs) requires proof-of-concept studies in order to establish the detectability of the CA and to predict the role of biodistribution in its uptake mechanisms. A promising approach is to carefully mimic the in vivo pharmacokinetic context with reduced experimental complexity compared to in vivo situations. A dedicated experimental system was built by combining a microfluidic slide and a radiofrequency probe based on a 6 mm diameter multiturn transmission-line resonator. Adherent KB cells were incubated with different concentrations of Gd. MRI data were acquired at 2.35T with a 3D gradient echo and a resolution of 12.4 μm perpendicular to the cell layer. The longitudinal relaxation rate, R1 , was measured as a function of the amount of Gd internalized by the cells. R1 measurements for different Gd concentrations per cell were performed using data with an signal-to-noise ratio (SNR) of 100. Relaxation-rate variations ΔR1 of 0.035 s(-1) were measured. A quenching effect was observed at Gd concentrations above 20 fmol/cell. Our results suggest that this dedicated experimental system is suitable for specifically assessing new high-relaxivity targeted CAs under real-time uptake conditions.

A comparative study of dewatering ofPinus radiatasapwood using supercritical CO2and conventional forced air-drying viain situmagnetic resonance microimaging (MRI)

AbstractA comparison of moisture loss fromPinus radiatasapwood by conventional forced air-drying and a novel supercritical carbon dioxide (scCO2) dewatering process has been examinedin situusing magnetic resonance microimaging. Air-drying results in the nonuniform removal of moisture within the wood volume, leading to a dry core and wet perimeter where water evaporated, whereas the scCO2dewatering process resulted in moisture expulsion more uniformly throughout the volume of the specimen, especially so within the earlywood.