ABSTRACT
References .........................................................................................................406
Most of the clinical magnetic resonance (MR) scanners being used mainly for MR imaging allow additionally the acquisition of MR spectra. In MR spectroscopy, information about the distribution of chemical compounds in a chosen volume of interest can be obtained, and signals from various nuclei present in the compounds can be observed. Feasible nuclei for
in vivo
measurements on patients are hydrogen-1, phosphorus-31, carbon-13, and fluorine-19. The most frequently used nucleus for
in vivo
MR spectroscopy is hydrogen-1. This nucleus consists only of one proton, and this measurement technique is therefore often
termed
proton spectroscopy
(H-MRS). If a spectroscopic examination is performed under ideal conditions with
in vitro
samples of human tissue, a great variety of signals can be observed in H-MRS. Under the limitations of
in vivo
examinations, signals from only a few metabolites can be clearly identified in the spectrum. The metabolites with the signals that are easiest to evaluate are creatine, choline, and
N
-
acetyl aspartate (NAA), which is a neurotransmitter observed predominantly in examinations of brain and spinal cord. Signals from other metabolites such as glutamate, glutamine, or citrate can be studied, if advanced measurement and evaluation techniques are applied, but many other molecules remain invisible in spectroscopic examinations due to their low concentration within the tissue, or due to short relaxation times or strong coupling effects. The challenge of
in vivo
spectroscopy is, therefore, the interpretation of signals of those few molecules that can be identified within the spectrum and that might give important additional diagnostic information.
