Abstracts

Rationale: Gamma-aminobutyric acid (GABA) is an important inhibitatory neurotransmitter in human brain with anticonvulsive character. Because of an increased interest in GABA metabolism we tested the reliability of special editing sequences which allow non-invasive intracerebral measurements of this neurotransmitter in healthy adults. Methods: We determined the reproducibility of results obtained with a J coupling based editing sequence using MEGA suppression on a 3T-TIM-Trio (Siemens) by placing single voxel spectroscopy (SVS) ROIs in left/right occipital lobe of subjects. Intra and inter-subject reproducibility was evaluated. 11 volunteers were measured in total, 3 probands repeatedly consecutively on 4 days. Comparison of side differences between left/right hemispheres was calculated. Results of GABA/Cr and GABA/H2O ratios were compared. Furthermore a detailed comparison of 2 different post-processing routines for the evaluation was accomplished. Integration of signals (GABA/Cr/H2O) was done using MestreC, compared to time domain line fitting routine(AMARES-jMRUI). Mean value, standard deviation(SD) and coefficient of variation(CV) were calculated among groups. Results: Using data from all subjects lower CVs can be observed for line fitting compared to integration. GABA/H2O ratio performs better than GABA/Cr or GABA alone (GABA/Cr: 13.6% and 21.55%; GABA/H2O: 14.8% and 21.68%; GABA: 20.62% and 26.42%). Single subject 4-day measurements showed slightly better intra- than inter-subject reproducibility (GABA/H2O 13.71%). No left/right difference could be found (GABA/H2O*1000: 0.139±0.022 and 0.133±0.018). Conclusions: With a CV of about 13% for GABA/Cr-, the technique turns out to be a precise and promising tool which easily detects changes of up to +300% found during antiepileptic drug intake. Despite of minor liquor contamination GABA/H2O-ratios are generally more reliable than GABA/tCr and GABA alone. Automated line-fitting performed much better than integration.