文档介绍：Optimization of Sequence Parameters
TE and TM to Detect and Separate
Glutamate and Glutamine by Localized
in vivo ic Resonance
Spectroscopy (MRS)
Diploma Thesis in Physical Chemistry
Helena Nilsson
Tutor: Gunther Helms, MR Research Centre,
Dept. Clinical Neuroscience, Karolinska Institutet
Institutionen för kemi
2002
Abstract
ic resonance spectroscopy (MRS) can be used for non-invasive clinical investigation
of patients. With proton MRS, up to 20 different metabolites can be observed in the human
brain. At the low field strengths available with whole body s it is more difficult to
resolve resonances than with conventional high-field NMR.
Glutamine and glutamate are important neurotransmitters and involved in the biochemistry of
neurons and glia cells in the brain. It is important to be able to determine the concentrations of
glutamine and glutamate in the brain.
Two localization sequences monly used in MRS: STEAM (stimulated echo
acquisition mode) that uses a stimulated echo and PRESS (point-resolved spectroscopy) that
uses a double spin echo for localization of the volume of interest (VOI). Both sequences
combine three orthogonal gradients with three pulses, to define the VOI at the intersection of
the three slices.
The echo time (TE) and mixing time (TM) in the STEAM sequence affects the appearance of
the spectra. During the TM, zero quantum coherences that are developed by the second pulse,
are evolving, causing different spectral pattern with different TMs.
The purpose of this work was to find the STEAM parameters TE and TM for which, within
technical limits, glutamine and glutamate resonances patterns differ the most, to allow the best
detection in human brain spectra by proton MRS.
Spectra of glutamine and glutamate and a mixture of glutamine and glutamate were measured
for various TE and TM with the STEAM sequence. For analysis of mixed sol