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P van Gelderen

Publications and source records attributed to P van Gelderen.

17 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↗
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

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↗
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

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↗
PubMed1994

Evaluation of restricted diffusion in cylinders. Phosphocreatine in rabbit leg muscle.

Interpretation of NMR diffusion data is complicated in the presence of diffusion barriers. In this study, restricted diffusion in cylinders is evaluated. A method is presented to determine the diameter of the cylinder and the unrestricted diffusion coefficient from the dependence of the trace of the diffusion tensor with diffusion time. This method is valid even if the orientation of the cylinders is unknown and varies within the sample. An example is given for the diffusion of phosphocreatine in the cylindrically shaped fibers of rabbit skeletal muscle.

Animals↗
PubMed1993

Diffusion in red blood cell suspensions: separation of the intracellular and extracellular NMR sodium signal.

It is shown that the signal of intracellular and extracellular sodium of red blood cells can be separated by a difference in diffusion. Comparison with proton diffusion experiments conducted in parallel showed that this difference was caused by restriction to the cell volume. The measured proton and sodium root mean square displacements agreed well with the cell dimensions. However, this experiment is limited to use in vitro by the required gradient strength.

Erythrocytes↗
PubMed1993

Fast echo-shifted gradient-recalled MRI: combining a short repetition time with variable T2* weighting.

The principles of a fast T2*-sensitized MR imaging method (Moonen et al., Magn. Reson. Med. 26, 184 (1992)) are extended to further increase T2* sensitivity. It is shown that the period of T2*-weighting can be lengthened by n TR-periods by appropriate gradient schemes without RF refocusing resulting in progressively delayed gradient-recalled echoes. This extension of the echo-shifting concept thus introduces large flexibility in the choice of T2*-weighting without changing total imaging time. The coherence pathway formalism is used to evaluate and describe the selection of the desired echo and the attenuation of unwanted coherences. The new techniques are demonstrated for tracking a bolus of susceptibility contrast agent in cat brain. Relative blood-volume maps are derived with expected contrast between white and gray matter.

Animals↗
PubMed1993

In vivo proton spectroscopy and spectroscopic imaging of [1-13C]-glucose and its metabolic products.

Metabolism of [1-13C]-glucose was studied in situ in cat brain using gradient-enhanced proton-detected heteronuclear spectroscopy. Proton detection of [1-13C]-glucose, [3-13C]-lactate, 4-[13C]-glutamine, 4-[13C]-glutamate and the combined signals 2-[13C]-glutamate/glutamine and 3-[13C]-glutamate/glutamine was achieved, despite the fact that some of the associated proton resonances are close to the water signal. Two-dimensional [1H-13C]-spectra demonstrate the possibility of in situ spectral assignment with 1H sensitivity and 13C resolution. Spectroscopic images of glucose and its metabolic products were also acquired, showing the possibility to study spatial dependence of metabolism.

Animals↗
PubMed1992

A fast gradient-recalled MRI technique with increased sensitivity to dynamic susceptibility effects.

A fast imaging method that is based on gradient-recalled echoes of spins whose excitation and echo formation are separated by more than one TR period is presented. This method does not incorporate chemical-shift refocusing and thus results in drastically increased sensitivity to dynamic susceptibility effects, while maintaining a short total imaging time. The efficiency of the new technique is demonstrated in dynamic contrast-enhanced experiments (bolus tracking) in the cat brain using a duration of 600 ms for each image. Blood volume maps are derived with expected contrast between white and gray matter.

Animals↗
PubMed1991

Restricted and anisotropic displacement of water in healthy cat brain and in stroke studied by NMR diffusion imaging.

The occlusion of the middle cerebral artery in cat brain was used as an experimental stroke model to investigate the physical basis of the recently reported lowered diffusion constant of water in acute infarcted brain tissue (Moseley et al., Magn. Reson. Med. 14, 330, 1990). The original findings were confirmed in this study of 12 animals investigated with the diffusion-sensitized stimulated echo sequence. The following additional results were obtained: First, the onset of significant lowering of the diffusion constant in the stroke area varied significantly (up to 2.5 h depending on the animal). Second, the affected area is much more clearly outlined in diffusion-weighted images than in T2-weighted images, even in the period between 3 to 12 h following occlusion. Third, for diffusion times between 50 and 2000 ms. the diffusion constant of water is independent of diffusion time in healthy tissue, as well as in the stroke area. Fourth, the diffusion anisotropy is similar in healthy and in stroke area and remains similar regardless of the diffusion time used.

Animals↗
PubMed1991

In vivo measurement of cerebral oxygen consumption and blood flow using 17O magnetic resonance imaging.

We used 17O NMR imaging techniques to measure the H2(17)O concentration in a 0.8-ml voxel in the cat brain following injection of an arterial bolus of enriched H2(17)O and during inhalation of enriched 17O2. We also measured the H2(17)O concentration in arterial blood during 17O2 inhalation. The data from the first measurement were used to calculate the blood flow in the voxel. The data from all three measurements were combined to calculate the oxygen consumption in the voxel. The values of cerebral blood flow and oxygen consumption calculated with 17O NMR techniques agree reasonably well with values calculated for a similar region of the cat brain using autoradiographic techniques.

Administration, Inhalation↗
PubMedDate not supplied

3D bolus tracking with frequency-shifted BURST MRI.

OBJECTIVE: Our goal was to develop and test a 3D bolus-tracking MR technique for perfusion imaging of normal and pathological (infarcted) human brain. MATERIALS AND METHODS: All experiments were performed on standard 1.5 T GE/Signa clinical scanners. Five normal volunteers and one patient with a subacute brain infarct were studied. Modified [frequency-shifted (FS)] BURST MRI was performed during injection of a bolus of Gd-DTPA (0.13 mmol/kg) in the antecubital vein. The 3D datasets were acquired with a time resolution of 2.2 s and an effective spatial resolution of 4.3 x 4.3 x 6.4 mm. Three-dimensional maps of blood volume and bolus arrival time were determined by fitting a synthetic curve to the intensity time course on a voxel-by-voxel basis. RESULTS: Both relative cerebral blood volume and arrival time maps demonstrated sensitivity to regional differences in blood supply in both normal brain and in the subacute brain infarction. The transit time maps showed arrival time delays of 5-7 s within and around the infarct and confirmed the diagnosis of left middle cerebral artery occlusion. CONCLUSION: The results of the measurements on both normal and diseased human brain demonstrated the ability to acquire valuable 3D information about brain perfusion using FS BURST MRI.

Adult↗