T₁‐FLAIR imaging during continuous head motion: Combining PROPELLER with an intelligent marker

Abstract

Purpose The purpose of this work is to describe a T1‐weighted fluid‐attenuated inversion recovery (FLAIR) sequence that is able to produce sharp magnetic resonance images even if the subject is moving their head throughout the acquisition. Methods The robustness to motion artifacts and retrospective motion correction capabilities of the PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) trajectory were combined with prospective motion correction. The prospective correction was done using an intelligent marker attached to the subject. This marker wirelessly synchronizes to the pulse sequence to measure the directionality and magnitude of the magnetic fields present in the MRI machine during a short navigator, thus enabling it to determine its position and orientation in the scanner coordinate frame. Three approaches to incorporating the marker‐navigator into the PROPELLER sequence were evaluated. The specific absorption rate, and subsequent scan time, of the T1‐weighted FLAIR PROPELLER sequence, was reduced using a variable refocusing flip‐angle scheme. Evaluations of motion correction performance were done with 4 volunteers and 3 types of head motion. Results During minimal out‐of‐plane movement, retrospective PROPELLER correction performed similarly to the prospective correction. However, the prospective clearly outperformed the retrospective correction when there was out‐of‐plane motion. Finally, the combination of retrospective and prospective correction produced the sharpest images even during large continuous motion. Conclusion Prospective motion correction of a PROPELLER sequence makes it possible to handle continuous, large, and high‐speed head motions with only minor reductions in image quality.

NeuroMix—A single‐scan brain exam

“…Possible candidates are another SSFSE, 43 in which increased SAR and reduced T1w contrast due to the long readout are the major concerns. The latter problem could also be taken care of by using a PROPELLER acquisition 9,44,45 . This, however, would result in longer scan times.…”

“…Unfortunately, in the case of large out-of-plane head motion, an inconsistent magnetization history can corrupt the image contrast even for the single-shot sequences. Inversion-prepared sequences such as T1-FLAIR or T2-FLAIR 23,45 are especially sensitive. It will be part of future work to also include prospective motion correction into NeuroMix to further improve its robustness.…”

“…The latter problem could also be taken care of by using a PROPELLER acquisition. 9,44,45 This, however, would result in longer scan times. An alternative option is a snapshot 2D-MPRAGE readout, which has proven to be very motion robust.…”

Control of a wireless sensor using the pulse sequence for prospective motion correction in brain MRI

“…The combination of T 1 -FLAIR PROPELLER with prospective motion correction has been shown to allow extremely motion robust imaging. 16 The implementation of the identifier pulses F I G U R E 7 Comparison of "TOGGLE" and "SHORT" modes with "SIMPLE" mode. The top plot group is for when navigators were turned off (no spatial encoding).…”

Comparison of prospective and retrospective motion correction in 3D‐encoded neuroanatomical MRI

“…However, RMC is less effective in 2D multi-slice segmented sequences when there is through-slice motion between segments. 30 3D-encoded acquisitions also suffer from k-space undersampling in the presence of head rotations, 8 which lead to violation of the Nyquist criterion and cannot be compensated by RMC using the nonuniform Fourier transform to reconstruct the irregularly sampled k-space. In principle, prospective correction of the acquisition will sample k-space as intended and thereby avoid such gaps in k-space.…”