Calibration-free regional RF shims for MR spectroscopy

Purpose: Sufficient control of the RF transmit field (B1+) in small regions-of-interest (ROIs) is critical for single voxel MR spectroscopy at ultra-high field. Static RF shimming, using parallel transmit (pTx), can improve B1+, but must be calibrated for each participant and ROI, which limits its applicability. Additionally, specific-absorption-rate (SAR) becomes hard to predict. This work aimed to find RF shims, which can be applied to any participant, to produce the desired |B1+| within pre-defined target ROIs. Methods: RF shims were found offline by joint-optimisation on a database, comprising B1+ maps from 11 subjects, considering ROIs in occipital cortex, hippocampus and posterior-cingulate, as well as the whole brain. The B1+ magnitude achieved using calibration-free RF shims was compared to a tailored shimming approach, and MR spectra were acquired using tailored and calibration-free RF shimming in 4 participants. Global and local 10g SAR deposition were modelled. Results: Calibration-free RF shims resulted in similar |B1+| in small ROIs compared to tailored shimming, in addition to producing spectra of excellent quality and equivalent SNR. Only a small database size was required. SAR deposition was reduced compared to operating in quadrature mode for all ROIs. Conclusion: This work demonstrates that static RF shims, optimised offline for small regions in single voxel MRS, avoid the need for lengthy B1+ mapping and pTx optimisation for each ROI and participant. Furthermore, power settings may be increased when using calibration-free shims to better take advantage of the flexibility provided by RF shimming for regional acquisition at ultra-high field.

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P1045 : Ultra-high-field MR-spectroscopy in NAFLD as non-invasive in-vivo tool for monitoring changes in fat and energy metabolism with potential identification of NASH and advanced fibrosis by saturation transfer technique

Journal of Hepatology ◽

10.1016/s0168-8278(15)31243-5 ◽

2015 ◽

Vol 62 ◽

pp. S739-S740 ◽

Cited By ~ 3

Author(s):

S. Traussnigg ◽

C. Kienbacher ◽

M. Gajdošík ◽

L. Valkovič ◽

H. Hofer ◽

...

Keyword(s):

Energy Metabolism ◽

Mr Spectroscopy ◽

High Field ◽

Advanced Fibrosis ◽

Saturation Transfer ◽

Ultra High Field ◽

Non Invasive ◽

High Field Mr

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Relating Eye Dominance to Neurochemistry in the Human Visual Cortex Using Ultra High Field 7-Tesla MR Spectroscopy

2019 International Conference on 3D Immersion (IC3D) ◽

10.1109/ic3d48390.2019.8976001 ◽

2019 ◽

Author(s):

I. Betina Ip ◽

Claudia Lunghi ◽

Uzay E. Emir ◽

Andrew J. Parker ◽

Holly Bridge

Keyword(s):

Visual Cortex ◽

Mr Spectroscopy ◽

High Field ◽

7 Tesla ◽

Ultra High Field ◽

Human Visual Cortex ◽

Eye Dominance

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Ultra-High Field Proton MR Spectroscopy in Early-Stage Amyotrophic Lateral Sclerosis

Neurochemical Research ◽

10.1007/s11064-017-2248-2 ◽

2017 ◽

Vol 42 (6) ◽

pp. 1833-1844 ◽

Cited By ~ 17

Author(s):

Ian Cheong ◽

Małgorzata Marjańska ◽

Dinesh K. Deelchand ◽

Lynn E. Eberly ◽

David Walk ◽

...

Keyword(s):

Amyotrophic Lateral Sclerosis ◽

Mr Spectroscopy ◽

High Field ◽

Early Stage ◽

Ultra High Field ◽

Proton Mr Spectroscopy ◽

Lateral Sclerosis

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Hilbert Fractal Inspired Dipoles for Passive RF Shimming in Ultra-High Field MRI

Photonics and Nanostructures - Fundamentals and Applications ◽

10.1016/j.photonics.2021.100988 ◽

2021 ◽

pp. 100988

Author(s):

Tania S. Vergara Gomez ◽

Marc Dubois ◽

Kaizad Rustomji ◽

Elodie Georget ◽

Tryfon Antonakakis ◽

...

Keyword(s):

High Field ◽

Ultra High Field ◽

High Field Mri ◽

Rf Shimming ◽

Ultra High Field Mri

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Visual looming and receding networks in awake marmosets investigated with fMRI

10.1101/749309 ◽

2019 ◽

Author(s):

Justine C. Cléry ◽

David J. Schaeffer ◽

Yuki Hori ◽

Kyle M. Gilbert ◽

Lauren K. Hayrynen ◽

...

Keyword(s):

High Field ◽

Visual Stimuli ◽

Occipital Cortex ◽

Peripersonal Space ◽

Emotional Reaction ◽

Potential Threat ◽

Ultra High Field ◽

Motion Direction ◽

Time To Collision ◽

Crucial Information

AbstractAn object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. This information (motion, direction, identity, time-to-collision, size, velocity) is analyzed by the brain in order to execute the appropriate behavioral responses depending on the context: fleeing, freezing, grasping, eating, exploring. In the current study, we performed ultra-high-field functional MRI (fMRI) in awake marmosets to explore the patterns of brain activation elicited by visual stimuli looming toward or receding away from the monkey. We found that looming and receding visual stimuli both activate a large cortical network in frontal, parietal, temporal and occipital cortex in areas involved in the analysis of motion, shape, identity and features of the objects. Looming stimuli strongly activated a network composed of the pulvinar, superior colliculus, prefrontal cortex and temporal cortical areas. This may underlie the existence of an alert network that processes the visual stimuli looming toward their peripersonal space by extracting the crucial information brought by the stimulus and evaluating its potential consequences to the observer. We hypothesize that this network is involved in the planning of protective behaviors (e.g. fleeing or freezing) and in emotional reaction (e.g. anxiety, fear). These findings support the view that this network is preserved through evolution and that the marmoset is a viable model to study visual and multisensory processes by using fMRI to guide further invasive recordings and/or pharmacological manipulations.Significant statementAn object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. Here, we identified the functional network in non-human primates that was activated by visual stimuli looming toward or away from the animals using ultra-high-field functional magnetic resonance imaging. Our findings show that large cortical activations are elicited by both looming and receding visual conditions. However, some activations were specific to the looming condition, suggesting that the integration of cues in the looming direction rely on strong connections between cortical and subcortical areas, which allows primates to react properly for protecting themselves against a potential threat.

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