Christopher R Durst1, Navin Michael2, Nicholas J Tustison3, James T Patrie4, Prashant Raghavan5, Max Wintermark3, S Sendhil Velan6. 1. Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA. Electronic address: cdurst@virginia.edu. 2. Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore. 3. Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA. 4. Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA. 5. Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland, Baltimore, MD, USA. 6. Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore; Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore, Singapore; Clinical Imaging Research Centre, Agency for Science, Technology and Research, Singapore, NUS-A*STAR, Singapore.
Abstract
PURPOSE: Rapid regional fluctuations in GABA may result in inhomogeneous concentrations throughout the brain parenchyma. The goal of this study is to provide further insight into the natural distribution of GABA throughout the brain and thus determine if a surrogate site may be used for spectroscopy when evaluating motor diseases, neurological disorders, or psychiatric dysfunction. MATERIALS AND METHODS: In this prospective study, eight healthy volunteers underwent spectroscopic evaluation of the frontal lobe, occipital lobe, lateral temporal lobe, basal ganglia, and both hippocampi using a spin echo variant of a J-difference editing method. Knowledge of the relative peak intensities of the macromolecule peaks at 3ppm and 0.9ppm was used to correct the contribution of co-edited macromolecules to the GABA peak at 3ppm. The GABA values were internally referenced to NAA. Linear regression was used to normalize the effect of regional tissue-fraction variation on the GABA/NAA values. A one-way ANOVA was performed with Tukey's multiple comparison test to compare the normalized GABA/NAA values in each pair of locations. RESULTS: After accounting for the macromolecule contribution to the GABA signal and correction for tissue fraction variation, the normalized GABA/NAA ratios differ significantly between the six brain locations (p<0.001). Pairwise comparisons of the corrected normalized GABA/NAA ratios show statistically significant variation between the frontal lobe and the basal ganglia, frontal and lateral temporal lobes, and frontal lobe and right hippocampus. Variations in the normalized GABA/NAA ratios trend toward significance between the frontal lobe and left hippocampus, occipital lobe and the frontal lobe, occipital lobe and basal ganglia, and occipital lobe and right hippocampus. CONCLUSION: Our study suggests that GABA concentration is inhomogeneous throughout the parenchyma. Studies evaluating the role of GABA must carefully consider voxel placement when incorporating spectroscopy.
PURPOSE: Rapid regional fluctuations in GABA may result in inhomogeneous concentrations throughout the brain parenchyma. The goal of this study is to provide further insight into the natural distribution of GABA throughout the brain and thus determine if a surrogate site may be used for spectroscopy when evaluating motor diseases, neurological disorders, or psychiatric dysfunction. MATERIALS AND METHODS: In this prospective study, eight healthy volunteers underwent spectroscopic evaluation of the frontal lobe, occipital lobe, lateral temporal lobe, basal ganglia, and both hippocampi using a spin echo variant of a J-difference editing method. Knowledge of the relative peak intensities of the macromolecule peaks at 3ppm and 0.9ppm was used to correct the contribution of co-edited macromolecules to the GABA peak at 3ppm. The GABA values were internally referenced to NAA. Linear regression was used to normalize the effect of regional tissue-fraction variation on the GABA/NAA values. A one-way ANOVA was performed with Tukey's multiple comparison test to compare the normalized GABA/NAA values in each pair of locations. RESULTS: After accounting for the macromolecule contribution to the GABA signal and correction for tissue fraction variation, the normalized GABA/NAA ratios differ significantly between the six brain locations (p<0.001). Pairwise comparisons of the corrected normalized GABA/NAA ratios show statistically significant variation between the frontal lobe and the basal ganglia, frontal and lateral temporal lobes, and frontal lobe and right hippocampus. Variations in the normalized GABA/NAA ratios trend toward significance between the frontal lobe and left hippocampus, occipital lobe and the frontal lobe, occipital lobe and basal ganglia, and occipital lobe and right hippocampus. CONCLUSION: Our study suggests that GABA concentration is inhomogeneous throughout the parenchyma. Studies evaluating the role of GABA must carefully consider voxel placement when incorporating spectroscopy.
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