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Biomedical subjects

C T Moonen

Publications and source records attributed to C T Moonen.

At least 19 recordsLinked to original sources
PubMed1996

Single-shot diffusion MRI of human brain on a conventional clinical instrument.

A single-shot diffusion MRI technique on a standard clinical 1.5T scanner is presented. The method incorporates the following elements: (a) an inversion RF pulse followed by a delay of 1.3 s to null cerebral spinal fluid (CSF) signal, (b) a stimulated echo sequence (TE = 56 ms, TM = 100 ms) to obtain strong diffusion weighting, (c) a single-shot gradient- and spin-echo (GRASE) sequence for imaging with a modified k-space trajectory and Carr-Purcell Meiboom-Gill (CPMG)-phase cycle. The trace of the diffusion coefficient obtained with this approach is in good agreement with values reported for animal brain, and for recent human studies. It is demonstrated that single-shot diffusion imaging of human brain is feasible on an unmodified standard instrument without high-gradient slew rate or extreme field homogeneity.

Brain↗
PubMed1996

Fast 3D functional magnetic resonance imaging at 1.5 T with spiral acquisition.

A new method to perform rapid 3D fMRI in human brain is introduced and evaluated in normal subjects, on a standard clinical scanner at 1.5 Tesla. The method combines a highly stable gradient echo technique with a spiral scan method, to detect brain activation related changes in blood oxygenation with high sensitivity. A motor activation paradigm with a duration of less than 5 min, performed on 10 subjects, consistently showed significant changes in signal intensity in the area of the motor cortex. In all subjects, these changes survived high statistical thresholds.

Brain↗
PubMed1996

Unraveling diffusion constants in biological tissue by combining Carr-Purcell-Meiboom-Gill imaging and pulsed field gradient NMR.

A diffusion-weighted multi-spin-echo pulse sequence is presented, which allows for simultaneous measurement of T2, the fractional amplitude, and the diffusion constant of different fractions. Monte Carlo simulations demonstrate an improvement of this sequence with respect to the accuracy of diffusion constant and fractional amplitude for slow exchange. Examples are shown for a simple phantom containing two fractions. In addition, experiments on cat brain in healthy condition and following occlusion of the middle cerebral artery show that the fractional amplitude and the diffusion constant of cerebral spinal fluid and normal brain tissue can be analyzed within each pixel with acceptable accuracy.

Animals↗
PubMed1996

Functional mapping of human sensorimotor cortex with 3D BOLD fMRI correlates highly with H2(15)O PET rCBF.

Positron emission tomography (PET) functional imaging is based on changes in regional cerebral blood flow (rCBF). Functional magnetic resonance imaging (fMRI) is based on a variety of physiological parameters as well as rCBF. This study is aimed at the cross validation of three-dimensional (3D) fMRI, which is sensitive to changes in blood oxygenation, with oxygen-15-labeled water (H2(15)O) PET. Nine normal subjects repeatedly performed a simple finger opposition task during fMRI scans and during PET scans. Within-subject statistical analysis revealed significant ("activated") signal changes (p < 0.05, Bonferroni corrected for number of voxels) in contralateral primary sensorimotor cortex (PSM) in all subjects with fMRI and with PET. With both methods, 78% of all activated voxels were located in the PSM. Overlap of activated regions occurred in all subjects (mean 43%, SD 26%). The size of the activated regions in PSM with both methods was highly correlated (rho = 0.87, p < 0.01). The mean distance between centers of mass of the activated regions in the PSM for fMRI versus PET was 6.7 mm (SD 3.0 mm). Average magnitude of signal change in activated voxels in this region, expressed as z-values adapted to timeseries, zt, was similar (fMRI 5.5, PET 5.3). Results indicate that positive blood oxygen level-dependent (BOLD) signal changes obtained with 3D principles of echo shifting with a train of observations (PRESTO) fMRI are correlated with rCBF, and that sensitivity of fMRI can equal that of H2(15)O PET.

Adult↗
PubMed1996

Regionally specific pattern of neurochemical pathology in schizophrenia as assessed by multislice proton magnetic resonance spectroscopic imaging.

OBJECTIVE: Several single-voxel proton magnetic resonance spectroscopy (1H-MRS) studies of patients with schizophrenia have found evidence of reductions of N-acetyl-aspartate (NAA) concentrations in the temporal lobes. Multislice proton magnetic resonance spectroscopy imaging (1H-MRSI) permits simultaneous acquisition and mapping of NAA, choline-containing compounds (CHO), and creatine/phosphocreatine (CRE) signal intensities from multiple whole brain slices consisting of 1.4-ml single-volume elements. We have used 1H-MRSI to assess the regional specificity of previously reported changes of metabolite signal intensities in schizophrenia. Hippocampal volume was also measured to test the relationship between 1H-MRSI findings and tissue volume in this region. METHOD: Ratios of areas under the metabolite peaks of the proton spectra were determined (i.e., NAA/CRE, NAA/CHO, CHO/CRE) for multiple cortical and subcortical regions in 10 inpatients with schizophrenia. RESULTS: Patients showed significant reductions of NAA/CRE and NAA/CHO bilaterally in the hippocampal region and in the dorsolateral prefrontal cortex. There were no significant changes in CHO/CRE or in NAA ratios in any other area sampled. No significant correlation was found between metabolite ratios in the hippocampal region and its volume. CONCLUSIONS: NAA-relative signal intensity reductions in schizophrenia appear to be remarkably localized, involving primarily the hippocampal region and the dorsolateral prefrontal cortex, two regions implicated prominently in the pathophysiology of this disorder.

Adult↗
PubMed1995

Three-dimensional functional magnetic resonance imaging of human brain on a clinical 1.5-T scanner.

Functional magnetic resonance imaging (fMRI) is a tool for mapping brain function that utilizes neuronal activity-induced changes in blood oxygenation. An efficient three-dimensional fMRI method is presented for imaging brain activity on conventional, widely available, 1.5-T scanners, without additional hardware. This approach uses large magnetic susceptibility weighting based on the echo-shifting principle combined with multiple gradient echoes per excitation. Motor stimulation, induced by self-paced finger tapping, reliably produced significant signal increase in the hand region of the contralateral primary motor cortex in every subject tested.

Brain↗
PubMed1995

Incorporation of lactate measurement in multi-spin-echo proton spectroscopic imaging.

An improved multi-slice, multi-spin-echo proton spectroscopic imaging method for human brain is presented. The technique allows the reconstruction of lactate images, along with choline plus creatine, N-acetylaspartate, and lipid images from one single data set processed in three separate ways. The discrimination between resonances of lipid protons and lactate methyl protons is based on homonuclear spin-spin coupling. The reliability of the separation of the lipid and lactate contribution depends on the T2 of the lipid resonances. Measurements were performed on a standard 1.5 Tesla clinical scanner on healthy volunteers and a patient with high grade CNS lymphoma, demonstrating the ability to obtain high quality metabolite maps within 11 min.

Aspartic Acid↗
PubMed1995

Susceptibility insensitive single shot MRI combining BURST and multiple spin echoes.

A single shot MR imaging technique insensitive to magnetic susceptibility effects is introduced. The method allows multislice imaging in areas with poor magnetic field homogeneity, and can be implemented on standard clinical scanners. The design is based on the combination of a BURST excitation with multiple RF refocusing pulses. Images were obtained at 1.5 T on phantoms and human brain with a matrix size of 64 x 54 and a resolution of 4 x 4 mm in 230 ms.

Artifacts↗
PubMed1995

Analytical solution for phase modulation in BURST imaging with optimum sensitivity.

In order to improve the efficiency of BURST imaging, a new phase-modulation scheme of the DANTE-type RF excitation is proposed. It is shown that analytical optimization of the phase-modulation scheme with optimal SNR can be found for an arbitrary number N of subpulses in the RF excitation. Both theory and experiment indicate a maximum attainable gain in efficiency of the square root of N, compared to nonmodulated (constant-phase) excitation schemes.

Humans↗
PubMed1995

Brain mapping with functional MR imaging: comparison of gradient-echo--based exogenous and endogenous contrast techniques.

PURPOSE: To compare directly the two most widely used methods of functional magnetic resonance (MR) imaging--dynamic contrast material-enhanced MR imaging and blood oxygenation level-dependent (BOLD) MR imaging. MATERIALS AND METHODS: Five healthy volunteers underwent dynamic contrast-enhanced and BOLD MR imaging with a conventional 1.5-T MR unit during visual stimulation and a dark control state. BOLD studies were performed with a gradient-echo sequence, and dynamic MR imaging was performed with an echo-shifted gradient-echo sequence after intravenous administration of a bolus of gadopentetate dimeglumine. RESULTS: A significantly greater percentage signal change was found with dynamic MR imaging than with the BOLD technique. The extent of area activated was also significantly greater. CONCLUSION: With standard clinical imagers and these gradient-echo-based techniques, greater percentage activation and area of activation can be achieved with dynamic MR imaging than with BOLD MR imaging.

Brain↗
PubMed1995

Brain regional distribution pattern of metabolite signal intensities in young adults by proton magnetic resonance spectroscopic imaging.

Proton magnetic resonance spectroscopy (1H-MRS) is evolving from single-volume localized acquisitions to multiple-volume acquisitions using magnetic resonance spectroscopic imaging (1H-MRSI). The normal regional patterns of 1H-MRSI-detectable metabolite signal intensities have yet to be established. We studied 13 healthy young adults with a multiple-section 1H-MRSI technique. The metabolite signals measured were N-acetylaspartate (NA), choline-containing compounds (CHO), creatine-phosphocreatine (CRE), and lactate. Ten neuroanatomic regions (nine bilateral) were identified in gray matter, white matter, and basal nuclei. Analysis of the data led to the following conclusions: (1) NA and CHO signals from centrum semiovale (CSO) can be used as a normalizing factor to reduce intersubject variability due to external causes; (2) in normal human brain, there is no left versus right asymmetry in the regions studied; (3) statistically significant patterns of signal distribution of NA, CHO, and CRE can be identified in normal human brain; and (4) CSO-normalized metabolite signal intensities and metabolite ratios complement each other for the detection of significant regional differences.

Adult↗
PubMed1994

Multislice proton magnetic resonance spectroscopic imaging in X-linked adrenoleukodystrophy.

Multislice proton magnetic resonance spectroscopic imaging permits metabolic analysis of brain tissue in vivo by data acquisition in four oblique axial slices, each 15-mm thick and divided into 0.8-ml single-volume elements. We applied this technique to the systematic study of 25 patients with adrenoleukodystrophy: 3 with the severe childhood or adult cerebral form of the disease, 5 with adrenomyeloneuropathy, 12 with no demonstrable neurological involvement, and 5 women heterozygous for adrenoleukodystrophy who had some degree of neurological disability. Abnormalities on magnetic resonance spectroscopic imaging included a reduction in N-acetyl aspartate, an increase in choline-containing compounds, and at times, an increase in lactate. Five patients showed abnormalities in the presence of normal-appearing magnetic resonance images, and in 8 other patients the alterations on spectroscopic images were more severe than those demonstrable by magnetic resonance imaging. Correlation with clinical course suggests that an increase in the choline-containing compounds is associated with an active demyelinative process, whereas such compounds are not elevated in lesions that are stable. We conclude that magnetic resonance spectroscopic imaging is a more sensitive indicator of early neurological involvement than is magnetic resonance imaging, and that the character of abnormalities detected by the former technique may serve as a gauge of the degree of activity of the demyelinating process and as a guide to the selection and evaluation of therapeutic approaches.

Adolescent↗
PubMed1994

Water diffusion and acute stroke.

The occlusion of the middle cerebral artery was used as an experimental acute stroke model in 30 cats. The diffusion of water was followed by diffusion-sensitized MRI between 1 and 15 h after induction of stroke. It is demonstrated that images representing the trace of the diffusion tensor provide a much more accurate delineation of affected area than images representing the diffusion in one direction only. The reason is that the strong contrast caused by the anisotropy and orientation of myelin fibers is completely removed in the trace of the diffusion tensor. The trace images show a small contrast between white and gray matter. The diffusion coefficient of white matter is decreased in acute stroke to approximately the same extent as gray matter. It is further shown that the average lifetime of water in extra and intracellular space is shorter than 20 ms both for healthy and ischemic tissue indicating that myelin fibers are permeable to water. The anisotropy contrast did not change before or after induction of stroke, nor after sacrifice. Together, these observations are consistent with the view that the changes in water diffusion during acute stroke are directly related to cytotoxic oedema, i.e., to the change in relative volume of intra- and extracellular spaces. Changes in membrane permeability do not appear to contribute significantly to the changes in diffusion.

Acute Disease↗
PubMed1994

3-dimensional functional imaging of human brain using echo-shifted FLASH MRI.

A 3-dimensional MRI method has been developed for functional mapping of the human brain, based on blood oxygenation level dependent (BOLD) contrast mechanisms. The method uses recently introduced principles of echo-shifted FLASH to acquire a single 3D data set in 20 s. The technique was tested on a conventional 1.5 Tesla clinical scanner with a standard head coil using visual stimulation with a 8 Hz flashing white light, or a varying checkerboard pattern. Areas of increased signal intensity were identified in the visual cortex, consistent with the known functional organization.

Brain↗
PubMed1994

Fast volume scanning with frequency-shifted BURST MRI.

We introduce a modified BURST imaging technique with reduced saturation effects and improved signal-to-noise ratio. The method applies a frequency shift to the RF excitation pulse on successive repetitions. It allows collection of 3D datasets of human brain within a few seconds, on a standard clinical scanner at 1.5 Tesla.

Brain↗