Advanced Brain Imaging
MR SpectroscopySpectral Editing
The detection and quantification of brain metabolites in 1H-MRS is often hampered by signal overlap and J-coupling evolution, which changes the phase of the acquired resonances. Spectral editing aims at resolving this problem by filtering out certain resonances from a background of other signals on the basis of their J-coupling behavior. MEGA-PRESS is a difference editing technique that uses frequency-selective refocusing pulses to selectively refocus the J-coupling evolution of specific resonances, e.g. arising from g-aminobutyric acid (GABA), an important inhibitory neurotransmitter in the human brain. Subtracting two spectra from each other, acquired with and without frequency-selective refocusing and thus with a differently phased GABA resonance, eliminates the overlapping creatine signal. In our group, this method is applied in psychiatric studies where GABA is used as an important metabolic marker. Furthermore, the technique is adapted and validated for the detection of other J-coupled metabolites such as lactate.
Real-time correction of MRS experiments
MRI and MRS experiments are often affected by subject motion and system imperfections arising from field inhomogeneities, field drifts and eddy currents. While MRI artefacts can usually readily be identified by the experienced radiologist, artefacts in MRS scans are much harder to recognize and can therefore give rise to false diagnoses in clinical examinations. Furthermore, MRS experiments are particularly susceptible to motion and system instabilities due to their long scan times. In our group we implement techniques aiming at the reduction of these artifacts. Lineshape distortions in MRS scans arising from hardware imperfections such as frequency drifts and eddy currents can be corrected with the interleaved reference scan method. Besides, we apply prospective motion correction to mitigate artifacts arising from subject motion. This method uses an optical camera for the acquisition of motion information, which is then fed back to the measurement control unit of the MR scanner where it is used to update RF pulses and gradients of the MRS sequence in real time.
Tel.: +49 761 270-93750
E-Mail: thomas.lange@uniklinik-freiburg.de
University Medical Center Freiburg
Dept. of Radiology · Medical Physics
Killianstr. 5a
79106 Freiburg