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BACKGROUND Effects of beta-amyloid accumulation on neuronal function precede the clinical manifestation of Alzheimer's disease (AD) by years and affect distinct cognitive brain networks. As previous studies suggest a link between beta-amyloid and dysregulation of excitatory and inhibitory neurotransmitters, we aimed to investigate the impact of GABA and glutamate on beta-amyloid related functional connectivity. METHODS 29 cognitively unimpaired old-aged adults (age = 70.03 ± 5.77 years) were administered 11C-Pittsburgh Compound B (PiB) positron-emission tomography (PET), and MRI at 7 Tesla (7T) including blood oxygen level dependent (BOLD) functional MRI (fMRI) at rest for measuring static and dynamic functional connectivity. An advanced 7T MR spectroscopic imaging (MRSI) sequence based on the free induction decay acquisition localized by outer volume suppression' (FIDLOVS) technology was used for gray matter specific measures of GABA and glutamate in the posterior cingulate and precuneus (PCP) region. RESULTS GABA and glutamate MR-spectra indicated significantly higher levels in gray matter than in white matter. A global effect of beta-amyloid on functional connectivity in the frontal, occipital and inferior temporal lobes was observable. Interactive effects of beta-amyloid with gray matter GABA displayed positive PCP connectivity to the frontomedial regions, and the interaction of beta-amyloid with gray matter glutamate indicated positive PCP connectivity to frontal and cerebellar regions. Furthermore, decreased whole-brain but increased fronto-occipital and temporo-parietal dynamic connectivity was found, when GABA interacted with regional beta-amyloid deposits in the amygdala, frontal lobe, hippocampus, insula and striatum. CONCLUSIONS GABA, and less so glutamate, may moderate beta-amyloid related functional connectivity. Additional research is needed to better characterize their interaction and potential impact on AD.

MRI with zero echo time is a robust, fast, and silent approach for three-dimensional (3-D) imaging of samples with short transverse relaxation times. In this article, the principles of acquiring and reconstructing data with zero echo time are described and complemented by discussions of implementation details, potential limitations, and selected applications, as well as advanced and related techniques. MR imaging of samples with very short T2s requires spatial encoding and data acquisition to be started and completed rapidly after signal creation. One powerful way of meeting these requirements is with 3-D radial center-out k-space encoding. In particular, when RF excitation is performed after switching on the projection gradient, such schemes achieve an echo time of zero and immediately have available maximum k-space speed. MRI with zero echo time poses two major challenges. First, RF pulses need to be of high bandwidth to uniformly excite the full range of Larmor frequencies induced by the projection gradient. Second, transmit–receive switching results in an initial period of dead time, because of which a certain range of data in the center of k-space is not acquired. This can be handled by acquisition oversampling in conjunction with algebraic image reconstruction.