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The aim of this work is to develop a fast and robust CEST sequence in order to allow the acquisition of a whole-brain imaging volume after a single preparation block (snapshot acquisition).A 3D-CEST sequence with an optimized 3D-EPI readout module was developed, which acquires the complete k-space data following a single CEST preparation for 1 saturation offset. Whole-brain mapping of the Z-spectrum with 2 mm isotropic resolution is achieved at 68 saturation frequencies in 5 minutes (4.33 s per offset). We analyzed the B 1 distribution in order to optimize B 1 correction and to provide accurate CEST quantification across the whole brain.We obtained maps for 3 different CEST contrasts from 4 healthy subjects. Based on our B 1 distribution analysis, we conclude that 3 B 1 sampling points allow for sufficient compensation of B 1 variations across most of the brain. Two brain regions, the cerebellum and the temporal lobes, are difficult to quantify at 7 T due to very low B 1 that was achieved in these regions.The proposed sequence enables robust acquisition of 2 mm isotropic whole-brain CEST maps at 7 Tesla within a total scan time of 16 minutes.

Purpose To develop a reconstruction pipeline that intrinsically accounts for both simultaneous multislice echo planar imaging (SMS-EPI) reconstruction and dynamic slice-specific Nyquist ghosting correction in time-series data. Methods After 1D slice-group average phase correction, the separate polarity (i.e., even and odd echoes) SMS-EPI data were unaliased by slice GeneRalized Autocalibrating Partial Parallel Acquisition. Both the slice-unaliased even and odd echoes were jointly reconstructed using a model-based framework, extended for SMS-EPI reconstruction that estimates a 2D self-phase map, corrects dynamic slice-specific phase errors, and combines data from all coils and echoes to obtain the final images. Results The percentage ghost-to-signal ratios (%GSRs) and its temporal variations for MB3Ry 2 with a field of view/4 shift in a human brain obtained by the proposed dynamic 2D and standard 1D phase corrections were 1.37 ± 0.11 and 2.66 ± 0.16, respectively. Even with a large regularization parameter λ applied in the proposed reconstruction, the smoothing effect in fMRI activation maps was comparable to a very small Gaussian kernel size 1 × 1 × 1 mm3 . Conclusion The proposed reconstruction pipeline reduced slice-specific phase errors in SMS-EPI, resulting in reduction of GSR. It is applicable for functional MRI studies because the smoothing effect caused by the regularization parameter selection can be minimal in a blood-oxygen-level-dependent activation map.

To investigate a method for rapid water excitation with minimal radiofrequency power deposition for efficient functional MRI at ultrahigh fields.The suitability of the spectral response of a single rectangular radiofrequency pulse (rect) as a replacement of conventional fat saturation in segmented three-dimensional (3D) echo planar imaging (EPI) is explored. A pulse duration formula for lipid signal nulling independent of the small-tip-angle approximation is derived and tested by means of simulations and experiments at 3 and 7 Tesla (T).Compared with conventional binomial-11 water excitation, the single rect method is more selective and less sensitive to shim imperfections. In functional MRI, a significant measurement speedup (25%) and specific absorption rate reduction (from 44% to 1% at 7T) compared with conventional fat saturation are achieved. Furthermore, magnetization transfer effects are reduced resulting in up to 25% higher brain tissue signal-to-noise ratio.The proposed method is well suited for whole-brain functional MRI, not only at ultra-high fields, as it maximizes the sensitivity per unit time and at the same time minimizes radiofrequency power deposition. It requires little implementation effort and may thus be used in other spatially nonselective imaging methods that require fat suppression at minimal specific absorption rate and time requirements. Magn Reson Med 76:1517-1523, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Background The human amygdala plays a crucial role in processing social signals, such as face expressions, particularly fearful ones, and facilitates responses to them in face-sensitive cortical regions. This contributes to social competence and individual amygdala size correlates with that of social networks. While rare patients with focal bilateral amygdala lesion typically show impaired recognition of fearful faces, this deficit is variable, and an intriguing possibility is that other brain regions can compensate to support fear and social signal processing. Methods To investigate the brain's functional compensation of selective bilateral amygdala damage, we performed a series of behavioral, psychophysiological, and functional magnetic resonance imaging experiments in two adult female monozygotic twins (patient 1 and patient 2) with equivalent, extensive bilateral amygdala pathology as a sequela of lipoid proteinosis due to Urbach-Wiethe disease. Results Patient 1, but not patient 2, showed preserved recognition of fearful faces, intact modulation of acoustic startle responses by fear-eliciting scenes, and a normal-sized social network. Functional magnetic resonance imaging revealed that patient 1 showed potentiated responses to fearful faces in her left premotor cortex face area and bilaterally in the inferior parietal lobule. Conclusions The premotor cortex face area and inferior parietal lobule are both implicated in the cortical mirror-neuron system, which mediates learning of observed actions and may thereby promote both imitation and empathy. Taken together, our findings suggest that despite the pre-eminent role of the amygdala in processing social information, the cortical mirror-neuron system may sometimes adaptively compensate for its pathology.