An equal‐TE ultrafast 3D gradient‐echo imaging method with high tolerance to magnetic susceptibility artifacts: Application to BOLD functional MRI

Abstract

To develop an ultrafast 3D gradient echo-based MRI method with constant TE and high tolerance to B 0 inhomogeneity, dubbed ERASE (equal-TE rapid acquisition with sequential excitation), and to introduce its use in BOLD functional MRI (fMRI). Theory and Methods: Essential features of ERASE, including spin behavior, were characterized, and a comparison study was conducted with conventional EPI. To demonstrate high tolerance to B 0 inhomogeneity, in vivo imaging of the mouse brain with a fiber-optic implant was performed at 9.4 T, and human brain imaging (including the orbitofrontal cortex) was performed at 3 T and 7 T. To evaluate the performance of ERASE in BOLD-fMRI, the characteristics of SNR and temporal SNR were analyzed for in vivo rat brains at 9.4 T in comparison with multislice gradientecho EPI. Percent signal changes and t-scores are also presented. Results: For both mouse brain and human brain imaging, ERASE exhibited a high tolerance to magnetic susceptibility artifacts, showing much lower distortion and signal dropout, especially in the regions involving large magnetic susceptibility effects. For BOLD-fMRI, ERASE provided higher temporal SNR and t-scores than EPI, but exhibited similar percent signal changes in in vivo rat brains at 9.4 T. Conclusion: When compared with conventional EPI, ERASE is much less sensitive, not only to EPI-related artifacts such as Nyquist ghosting, but also to B 0 inhomogeneity including magnetic susceptibility effects. It is promising for use in BOLD-fMRI, providing higher temporal SNR and t-scores with constant TE when compared with EPI, although further optimization is needed for human fMRI. K E Y W O R D S constant echo time, echo-planar imaging, magnetic susceptibility artifacts, quadratic-phase encoding, spatiotemporal encoding, ultrafast imaging How to cite this article: Ryu J-K, Jung WB, Yu J, et al. An equal-TE ultrafast 3D gradient-echo imaging method with high tolerance to magnetic susceptibility artifacts: Application to BOLD functional MRI.

Novel inductively coupled ear-bars (ICEs) to enhance restored fMRI signal from susceptibility compensation in rats

“…2015 ; Yoo et al. 2020 ; Ryu et al. 2021 ), these efforts are mostly focused on restoring lost signals in echo-planar imaging (EPI)-based blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) images over large scales across the entire brain.…”

“…Several studies have already been done to reduce susceptibility artifacts. An equal-TE ultrafast 3D gradient-echo imaging method was developed to provide high tolerance to magnetic susceptibility artifacts in rat cortex with optical fiber implantation at 9.4T ( Ryu et al. 2021 ).…”

Novel inductively-coupled ear-bars (ICEs) for fMRI signal enhancement in rat entorhinal cortex

“…Several studies have already been done to reduce susceptibility artifact. An equal-TE ultrafast 3D gradient-echo imaging method was developed to provide high tolerance to magnetic susceptibility artifacts in rat cortex with optical fiber implantation at 9.4 T [22]. Since the middle ear filled with air was separated from the external ear by the tympanic membrane [23], this membrane was penetrated and Fomblin Y [23] or toothpaste [24] were used to fill the ear cavities to restore susceptibility-induced MRI signal dropout.…”

“…In addition, magnetic susceptibility artifacts are prevalent on the boundary of air-containing ear cavities in rodents [20,21]. Although efforts have been made to reduce susceptibility artifacts [22][23][24][25], these efforts are mostly focused on restoring lost signals on EPI blood oxygen level-dependent (BOLD) fMRI images over large scales across the entire brain. It still remains challenging to achieve the true whole-brain fMRI imaging.…”