Thomas Neuberger

In vivo detection limits of magnetically labeled embryonic stem cells in the rat brain using high-field (17.6 T) magnetic resonance imaging.

Stem cell transplantation is a promising therapeutic approach for several neurological disorders. However, it has yet to fulfill its high expectations, partially due to the lack of a reliable noninvasive method for monitoring the biodistribution of the grafted stem cells in vivo. We have used high-resolution magnetic resonance imaging (MRI) at 17.6 T, combined with efficient magnetic labeling of the stem cells with iron oxide nanoparticles, in order to assess the in vivo detection limit in small animal models. Injection of different concentrations of magnetically labeled stem cells in gel phantoms led to significant reductions in image intensity from small cellular clusters of less than 10 cells. To determine the detection limit in vivo, various numbers of both labeled and unlabeled cells were injected stereotactically into the striatum of rats. Significant hypointense signal changes were observed for 100 labeled cells. After injection of approximately 20 labeled cells, signal reduction at the injection site was observed but could not be assigned unambiguously to the cells. Our results show that high-field MRI allows tracking of a minimal number of cells in vivo, well below the number used in previous studies, opening the possibility of gaining new insights into cell migration and differentiation.

Surveying the plant’s world by magnetic resonance imaging

Understanding the way in which plants develop, grow and interact with their environment requires tools capable of a high degree of both spatial and temporal resolution. Magnetic resonance imaging (MRI), a technique which is able to visualize internal structures and metabolites, has the great virtue that it is non-invasive and therefore has the potential to monitor physiological processes occurring in vivo. The major aim of this review is to attract plant biologists to MRI by explaining its advantages and wide range of possible applications for solving outstanding issues in plant science. We discuss the challenges and opportunities of MRI in the study of plant physiology and development, plant-environment interactions, biodiversity, gene functions and metabolism. Overall, it is our view that the potential benefit of harnessing MRI for plant research purposes is hard to overrate.

Seed Architecture Shapes Embryo Metabolism in Oilseed Rape

This work investigates how metabolism and oil storage capacity of the growing embryo of oilseed rape is adjusted to developmental changes in its architecture. It shows that locally distinct growth conditions due to the folding of cotyledons cause metabolic heterogeneity that reflects at the level of pathway activity, metabolites, and storage products (oil/protein). Constrained to develop within the seed, the plant embryo must adapt its shape and size to fit the space available. Here, we demonstrate how this adjustment shapes metabolism of photosynthetic embryo. Noninvasive NMR-based imaging of the developing oilseed rape (Brassica napus) seed illustrates that, following embryo bending, gradients in lipid concentration became established. These were correlated with the local photosynthetic electron transport rate and the accumulation of storage products. Experimentally induced changes in embryo morphology and/or light supply altered these gradients and were accompanied by alterations in both proteome and metabolome. Tissue-specific metabolic models predicted that the outer cotyledon and hypocotyl/radicle generate the bulk of plastidic reductant/ATP via photosynthesis, while the inner cotyledon, being enclosed by the outer cotyledon, is forced to grow essentially heterotrophically. Under field-relevant high-light conditions, major contribution of the ribulose-1,5-bisphosphate carboxylase/oxygenase–bypass to seed storage metabolism is predicted for the outer cotyledon and the hypocotyl/radicle only. Differences between in vitro– versus in planta–grown embryos suggest that metabolic heterogeneity of embryo is not observable by in vitro approaches. We conclude that in vivo metabolic fluxes are locally regulated and connected to seed architecture, driving the embryo toward an efficient use of available light and space.

Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms and in vivo

It is important to accurately characterize the heating of tissues due to the radiofrequency energy applied during MRI. This has led to an increase in the use of numerical methods to predict specific energy absorption rate distributions for safety assurance in MRI. To ensure these methods are accurate for actual MRI coils, however, it is necessary to compare to experimental results. Here, we report results of some recent efforts to experimentally map temperature change and specific energy absorption rate in a phantom and in vivo where the only source of heat is the radiofrequency fields produced by the imaging coil. Results in a phantom match numerical simulation well, and preliminary results in vivo show measurable temperature increase. With further development, similar methods may be useful for verifying numerical methods for predicting specific energy absorption rate distributions and in some cases for directly measuring temperature changes and specific energy absorption rate induced by the radiofrequency fields in MRI experiments. Magn Reson Med, 2009.

The use of magnetic resonance spectroscopy in the subacute evaluation of athletes recovering from single and multiple mild traumatic brain injury.

Advanced neuroimaging techniques have shown promise in highlighting the subtle changes and nuances in mild traumatic brain injury (MTBI) even though clinical assessment has shown a return to pre-injury levels. Here we use ¹H-magnetic resonance spectroscopy (¹H-MRS) to evaluate the brain metabolites N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) in the corpus callosum in MTBI. Specifically, we looked at the NAA/Cho, NAA/Cr, and Cho/Cr ratios in the genu and splenium. We recruited 20 normal volunteers (NV) and 28 student athletes recovering from the subacute phase of MTBI. The MTBI group was categorized based upon the number of MTBIs and time from injury to ¹H-MRS evaluation. Significant reductions in NAA/Cho and NAA/Cr ratios were seen in the genu of the corpus callosum, but not in the splenium, for MTBI subjects, regardless of the number of MTBIs. MTBI subjects recovering from their first MTBI showed the greatest alteration in NAA/Cho and NAA/Cr ratios. Time since injury to ¹H-MRS acquisition was based upon symptom resolution and did not turn out to be a significant factor. We observed that as the number of MTBIs increased, so did the length of time for symptom resolution. Unexpected findings from this study are that MTBI subjects showed a trend of increasing NAA/Cho and NAA/Cr ratios that coincided with increasing number of MTBIs.

Effects of Subconcussive Head Trauma on the Default Mode Network of the Brain

Although they are less severe than a full blown concussive episodes, subconcussive impacts happen much more frequently and current research has suggested this form of head trauma may have an accumulative effect and lead to neurological impairment later in life. To investigate the acute effects that subconcussive head trauma may have on the default mode network of the brain resting-state, functional magnetic resonance was performed. Twenty-four current collegiate rugby players were recruited and all subjects underwent initial scanning 24 h prior to a scheduled full contact game to provide a baseline. Follow-up scanning of the rugby players occurred within 24 h following that game to assess acute effects from subconcussive head trauma. Differences between pre-game and post-game scans showed both increased connectivity from the left supramarginal gyrus to bilateral orbitofrontal cortex and decreased connectivity from the retrosplenial cortex and dorsal posterior cingulate cortex. To assess whether or not a history of previous concussion may lead to a differential response following subconcussive impacts, subjects were further divided into two subgroups based upon history of previous concussion. Individuals with a prior history of concussion exhibited only decreased functional connectivity following exposure to subconcussive head trauma, while those with no history showed increased connectivity. Even acute exposure to subconcussive head trauma demonstrates the ability to alter functional connectivity and there is possible evidence of a differential response in the brain for those with and without a history of concussion.

Quantitative analysis of peristaltic and segmental motion in vivo in the rat small intestine using dynamic MRI.

Conventional methods of quantifying segmental and peristaltic motion in animal models are highly invasive; involving, for example, the external isolation of segments of the gastrointestinal (GI) tract either from dead or anesthetized animals. The present study was undertaken to determine the utility of MRI to quantitatively analyze these motions in the jejunum region of anesthetized rats (N = 6) noninvasively. Dynamic images of the GI tract after oral gavage with a Gd contrast agent were acquired at a rate of six frames per second, followed by image segmentation based on a combination of three‐dimensional live wire (3D LW) and directional dynamic gradient vector flow snakes (DDGVFS). Quantitative analysis of the variation in diameter at a fixed constricting location showed clear indications of both segmental and peristaltic motions. Quantitative analysis of the frequency response gave results in good agreement with those acquired in previous studies using invasive measurement techniques. Principal component analysis (PCA) of the segmented data using active shape models resulted in three major modes. The individual modes revealed unique spatial patterns for peristaltic and segmental motility. Magn Reson Med, 2009.

Brain phenotypes in two FGFR2 mouse models for Apert syndrome

Apert syndrome (AS) is one of at least nine disorders considered members of the fibroblast growth factor receptor (FGFR) ‐1, ‐2, and ‐3–related craniosynostosis syndromes. Nearly 100% of individuals diagnosed with AS carry one of two neighboring mutations on Fgfr2. The cranial phenotype associated with these two mutations includes coronal suture synostosis, either unilateral (unicoronal synostosis) or bilateral (bicoronal synostosis). Brain dysmorphology associated with AS is thought to be secondary to cranial vault or base alterations, but the variation in brain phenotypes within Apert syndrome is unexplained. Here, we present novel three‐dimensional data on brain phenotypes of inbred mice at postnatal day 0 each carrying one of the two Fgfr2 mutations associated with AS. Our data suggest that the brain is primarily affected, rather than secondarily responding to skull dysmorphogenesis. Our hypothesis is that the skull and brain are both primarily affected in craniosynostosis and that shared phenogenetic developmental processes affect both tissues in craniosynostosis of Apert syndrome. Developmental Dynamics 239:987–997, 2010.

A multiscale lattice Boltzmann model of macro- to micro-scale transport, with applications to gut function

Nutrient absorption in the small intestine cannot occur until molecules are presented to the epithelial cells that line intestinal villi, finger-like protrusions under enteric control. Using a two-dimensional multiscale lattice Boltzmann model of a lid-driven cavity flow with ‘villi’ at the lower surface, we analyse the hypothesis that muscle-induced oscillatory motions of the villi generate a controlled ‘micro-mixing layer’ (MML) that couples with the macro-scale flow to enhance absorption. Nutrient molecules are modelled as passive scalar concentrations at high Schmidt number. Molecular concentration supplied at the cavity lid is advected to the lower surface by a lid-driven macro-scale eddy. We find that micro-scale eddying motions enhance the macro-scale advective flux by creating an MML that couples with the macro-scale flow to increase absorption rate. We show that the MML is modulated by its interactions with the outer flow through a diffusion-dominated layer that separates advection-dominated macro-scale and micro-scale mixed layers. The structure and strength of the MML is sensitive to villus length and oscillation frequency. Our model suggests that the classical explanation for the existence of villi—increased absorptive surface area—is probably incorrect. The model provides support for the potential importance of villus motility in the absorptive function of the small intestine.

High-resolution MR imaging of the rat spinal cord in vivo in a wide-bore magnet at 17.6 Tesla.

The objective was to demonstrate the feasibility and to evaluate the performance of high-resolution in vivo magnetic resonance (MR) imaging of the rat spinal cord in a 17.6-T vertical wide-bore magnet. A probehead consisting of a surface coil that offers enlarged sample volume suitable for rats up to a weight of 220 g was designed. ECG triggered and respiratory-gated gradient echo experiments were performed on a Bruker Avance 750 wide-bore spectrometer for high-resolution imaging. With T*2 values between 5 and 20 ms, good image contrast could be obtained using short echo times, which also minimizes motion artifacts. Anatomy of healthy spinal cords and pathomorphological changes in traumatically injured rat spinal cord in vivo could be visualized with microscopic detail. It was demonstrated that imaging of the rat spinal cord in vivo using a vertical wide-bore high-magnetic-field system is feasible. The potential to obtain high-resolution images in short scan times renders high-field imaging a powerful diagnostic tool.