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T G Noll

Publications and source records attributed to T G Noll.

4 recordsLinked to original sources
PubMed2001

Reducing oblique flow effects in interleaved EPI with a centric reordering technique.

Segmented interleaved echo planar imaging offers a fast and efficient approach to magnetic resonance angiography. Unfortunately, this technique is particularly sensitive to oblique flow in the imaging plane. In this work, a mathematical analysis of oblique flow effects for several types of k-space coverage is presented. The conventional linear acquisition scheme, an alternating centric and a nonalternating centric encoding scheme are compared with respect to their flow properties. It is shown both by simulations and imaging experiments that artifacts from oblique in-plane flow are effectively reduced by both centric reordered phase-encoding schemes. The nonalternating centric acquisition scheme is preferred to the alternating centric scheme due to the smoother phase error transition in k-space in the presence of obliquely-angled flow. Magn Reson Med 45:623-629, 2001.

Artifacts↗
PubMed1998

Device visualization for interventional MRI using local magnetic fields: basic theory and its application to catheter visualization.

This paper addresses one of the major problems in Interventional magnetic resonance imaging (MRI): the visualization of interventional devices. For visualization locally induced magnetic fields are used, which disturb the homogeneity of the main magnetic field of the MR scanner. This results in signal loss in the vicinity of the device due to intravoxel dephasing, and leads to a disturbance of the phase image. The local fields are established by a low current in a closed copper loop along the device. This method will be introduced as a means for catheter visualization. The basic theory behind this method is presented. Simulations are performed to determine the effect of intravoxel dephasing, without interfering effects like susceptibility or radio-frequency artifacts. Scanned and simulated data is used to verify the theoretical consideration. Different configurations of wire loops are discussed and two types of catheter visualization scans are proposed. Results from a pig study show that this methods holds promise for intravascular interventions under MRI guidance.

Animals↗
PubMed1997

Distributed large-scale simulation of magnetic resonance imaging.

The concept and the implementation of a parallelized and spin-based simulator for magnetic resonance (MR) imaging is presented. The dynamics of magnetization are modeled using the Bloch equation covering arbitrary radiofrequency (RF) pulses, gradients, main-field inhomogeneity, and relaxation. A temporal decomposition of a given sequence is introduced, leading to basic sequence elements called atoms. A concept of spatial sampling of the object by spins is proposed, in the course of which Shannon's sampling theorem must be respected. In biomedical MR imaging, spins can be modeled as noninteracting entities, permitting an efficient parallelization of the simulation. The simulator ParSpin was implemented on a heterogeneous, interconnected cluster of workstations based on existing message passing libraries. The communication overhead has been kept moderately small. The aggregate computing performance of many processors enables the research into very complex problems (e.g., three-dimensional or steady-state MR experiments requiring up to 10(6) spins). Additionally, ParSpin allows a comprehensive visualization for educational purposes.

Computer Simulation↗