Biomedical subjects

E T Ahrens

Publications and source records attributed to E T Ahrens.

7 recordsLinked to original sources

PubMed2001

Peripheral somatosensory fMRI in mouse at 11.7 T.

The feasibility of performing extremely-high resolution somatosensory fMRI in anesthetized mice using BOLD contrast at 11.7 T was investigated. A somatosensory stimulus was applied to the hindlimb of an alpha-chlorolose anesthetized mouse resulting in robust (p < 4 x 10(-3)) BOLD changes in somatosensory cortex and large veins. Percentage modulation of the MR signal in cortex exceeded 7%. Experiments that artificially modulated the inspired oxygen tension were also conducted; the results revealed large, heterogeneous, BOLD contrast changes in the mouse brain. In addition, T(1), T(2), and T(2)* values in gray matter at 11.7 T were evaluated. Discussion of the sensitivity limitations of BOLD fMRI in the tiny mouse central nervous system is presented. These methods show promise for the assessment of neurological function in mouse models of CNS injury and disease.

Animals↗

PubMed2001

In vivo observation of cavitation and embolism repair using magnetic resonance imaging.

Magnetic resonance imaging (MRI) was used to noninvasively monitor the status of individual xylem vessels in the stem of an intact, transpiring grape (Vitis vinifera) plant over a period of approximately 40 h. Proton density-weighted MRI was used to visualize the distribution of mobile water in the stem and individual xylem vessels were scored as either water or gas filled (i.e. embolized). The number of water-filled vessels decreased during the first 24 h of the experiment, indicating that approximately 10 vessels had cavitated during this time. Leaf water potentials decreased from -1.25 to -2.1 MPa during the same period. Watering increased leaf water potentials to -0.25 MPa and prevented any further cavitation. Refilling of xylem vessels occurred as soon as the lights were switched off, with the majority of vessels becoming refilled with water during the first 2 to 3 h in darkness. These measurements demonstrate that MRI can be used to monitor the functional status of individual xylem vessels, providing the first method to study the process of cavitation and embolism repair in intact plants.

Magnetic Resonance Imaging↗

PubMed2000

In vivo visualization of gene expression using magnetic resonance imaging.

High-resolution in vivo imaging of gene expression is not possible in opaque animals by existing techniques. Here we present a new approach for obtaining such images by magnetic resonance imaging (MRI) using an MRI contrast agent that can indicate reporter gene expression in living animals. We have prepared MRI contrast agents in which the access of water to the first coordination sphere of a chelated paramagnetic ion is blocked with a substrate that can be removed by enzymatic cleavage. Following cleavage, the paramagnetic ion can interact directly with water protons to increase the MR signal. Here, we report an agent where galactopyranose is the blocking group. This group renders the MRI contrast agent sensitive to expression of the commonly used marker gene, beta-galactosidase. To cellular resolution, regions of higher intensity in the MR image correlate with regions expressing marker enzyme. These results offer the promise of in vivo mapping of gene expression in transgenic animals and validate a general approach for constructing a family of MRI contrast agents that respond to biological activity.

Animals↗

PubMed1999

Looking deeper into vertebrate development.

Magnetic resonance imaging (MRI) is a non-invasive imaging method that provides three-dimensional (3-D) images of the internal structure of opaque objects, such as humans and mice. In optimal situations, spatial resolution can approach the micron level. Arbitrarily oriented single-slice images can be obtained in seconds, with full 3-D volume images taking tens of minutes to collect. The exquisite sensitivity of MRI to the local physical and chemical environment provides a wide range of mechanisms giving rise to intrinsic contrast in the MR experiment, thus providing images with dramatic differences between different tissue types (e.g. white vs grey matter, myelinated vs unmyelinated fibres, and brain parenchyma vs ventricles). The recent advent of physiologically sensitive MRI contrast agents opens up a wealth of new avenues of study, even including the in vivo imaging of gene expression.

Animals↗

PubMed1998

A model for MRI contrast enhancement using T1 agents.

Contrast in MRI relies on differences in the local environment of water and is often enhanced by using contrast agents. We present a simple model for evaluating the minimal contrast agent concentration required to produce "satisfactory" contrast enhancement in magnetic resonance images. Previous strategies have been based largely on empirical results for specific systems. The present tissue contrast model (TCM) can be applied to "conventional," targeted, or biochemically responsive agents. The model results are formulated so that only a small number of parameters are required to analyze a given scenario. The TCM is a particularly useful tool in the development of new classes of magnetic resonance contrast media. These agents will have the ability to target specific cells or tissue, and perhaps be able to report on their physiological status. As an example of the applicability of the TCM, we test it against in vivo magnetic resonance microscopy results in frog embryos that have focal cell populations labeled with contrast agent by using calibrated single-cell microinjection techniques.

Animals↗

PubMed1998

MR microscopy of transgenic mice that spontaneously acquire experimental allergic encephalomyelitis.

Pathology of fixed spinal cords from transgenic mice with a myelin basic protein (MBP) specific T cell receptor was investigated. These mice spontaneously acquire the demyelinating disease experimental allergic encephalomyelitis (EAE). Several complementary imaging modalities, all on the same tissues, were used to visualize lesions; these included high-field (11.7-T) microscopic diffusion tensor imaging (DTI), T2*-weighted imaging, and optical microscopy on histological sections. Lesions were predominantly in white matter around meninges and vasculature and appeared hyperintense in anatomical images. DTIs showed reduced diffusion anisotropy in the same hyperintense regions, consistent with inflammation and edema. Histology in the same tissues exhibited the characteristic pathology of EAE. Two techniques for visualizing the effective diffusion tensor fields are presented, which display direction, organization, and integrity of neuronal fibers. It is shown that DTI offers intriguing possibilities for visualizing axonal organization and lesions within white matter.

Algorithms↗

PubMedDate not supplied

Towards a microMRI atlas of mouse development.

This study investigates the potential of microscopic Magnetic Resonance Imaging to obtain information for 3D digital atlases of mouse development using fixed samples. Fixed samples allow direct comparison with already published atlases and provide a testing ground for future in vivo efforts. 3D MR images of mouse embryos (dpc 6.5-16) illustrate that the necessary contrast and level of detail is available with this technique. Diffusion weighted imaging, diffusion tensor imaging, and multi-valued data sets are presented as examples of uniquely MR methods of obtaining anatomical information. MRI is performed non-invasively on the intact sample, leaving open the possibility of other manipulations (e.g. classical histology, immunohistochemistry, in situ hybridization, and in vitro growth for unfixed samples) after conducting the MRI experiment.

Animals↗