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Ultra High Field - Profiting from Higher Magnetic Susceptibility

Functional MRI (fMRI)

An application which greatly benefits from Ultra High Field (UHF) MRI is Blood Oxygenation Level Dependent (BOLD) fMRI. The increased susceptibility effects at UHF translate into a greater observable BOLD signal change and therefore improved fMRI experiments [1].

Functional MRI is used to study functional connectivity to further understand brain function in health and disease [2]. Using the high sensitivity provided by UHF, high resolution fMRI preclinical experiments thus become feasible [3]. Functional sensitivity will additionally benefit from UHF in situations where thermal noise is dominant, as it is directly dependent on sensitivity and indirectly dependent on temporal noise [4]. This is the case for high resolution studies which are enabled at UHF [5].

Independent component analysis (ICA) identifies sets of bilateral cortical and striatal connectivity networks without á priori hypotheses

Independent component analysis (ICA) identifies sets of bilateral cortical and striatal connectivity networks without á priori hypotheses. Data acquired in in vivo rat brain at 11.7 Tesla [3]. Courtesy: Mathias Hoehn, Max-Planck-Institute for Neurological Research, Cologne, Germany

References:

[1] Duyn JH. The future of ultra-high field MRI and fMRI for study of the human brain. Neuroimage. 2012;62(2):1241-1248. doi:10.1016/j.neuroimage.2011.10.065.
www.ncbi.nlm.nih.gov/pmc/articles/PMC3389184/
[2] Kalthoff D, Hoehn H. Functional Connectivity MRI of the Rat Brain. Bruker Application Note 2012
Functional_Connectivity.pdf
[3] Seehafer JU, Hoehn H. Insights in the rat brain by high resolution BOLD functional MRI. Bruker Application Note 2011 BOLD_MRI_AppsNote_T13106.pdf
[4] Han SH, Son JP, Cho HJ, Park JY, Kim SG. Gradient‐echo and spin‐echo blood oxygenation level–dependent functional MRI at ultrahigh fields of 9.4 and 15.2 Tesla. Magnetic Resonance in Medicine. 2018; 1-10. doi: 10.1002/mrm.27457
www.ncbi.nlm.nih.gov/pubmed/30183108
[5] Uludağ K, Blinder P. Linking brain vascular physiology to hemodynamic response in ultra-high field MRI. NeuroImage. 2018; 168: 279-295. doi.org/10.1016/j.neuroimage.2017.02.063
www.ncbi.nlm.nih.gov/pubmed/28254456

SWI and QSM

In addition to BOLD imaging, further imaging applications which rely on high susceptibility effects combined with a high SNR and therefore benefit from UHF, are Susceptibility Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM) [6]. QSM can for example be applied in vivo to study the microvasculature in animal stroke models [7].

Ultra high resolution T2* weighted in vivo mouse brain data acquired at 15.2 Tesla with the MRI CryoProbe

Ultra high resolution T2* weighted in vivo mouse brain data acquired at 15.2 Tesla with an MRI CryoProbe. Method: FLASH, Resolution: (20 x 20) µm², Slice Thickness: 150 µm, Slices: 7, Scan time: 21 min. A/C) Magnitude images, two different slices. B/D) Corresponding phase images.

References:

[6] Duyn J. MR Susceptibility Imaging. Journal of magnetic resonance (San Diego, Calif : 1997). 2013;229:198-207. doi:10.1016/j.jmr.2012.11.013.
www.ncbi.nlm.nih.gov/pmc/articles/PMC3602381/

[7] Hsieh M-C, Tsai C-Y, Liao M-C, Yang J-L, Su C-H, Chen J-H. Quantitative Susceptibility Mapping-Based Microscopy of Magnetic Resonance Venography (QSM-mMRV) for In Vivo Morphologically and Functionally Assessing Cerebromicrovasculature in Rat Stroke Model. Jiang Q, ed. PLoS ONE. 2016;11(3):e0149602. doi:10.1371/journal.pone.0149602.
www.ncbi.nlm.nih.gov/pubmed/26974842