Serger Matthias, Stirnberg Rüdiger, Ehses Philipp, Stöcker Tony
MR Physics, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
Department of Physics & Astronomy, University of Bonn, Bonn, Germany.
Magn Reson Med. 2025 Jul;94(1):105-118. doi: 10.1002/mrm.30441. Epub 2025 Jan 23.
MR-based FID navigators (FIDnavs) do not require gradient pulses and are attractive for prospective motion correction (PMC) due to short acquisition times and high sampling rates. However, accuracy and precision are limited and depend on a separate calibration measurement. Besides FIDnavs, stationary NMR field probes are also capable of measuring local, motion-induced field changes. In this work, a linear model is calibrated between field probe data and motion parameters analog to FIDnav calibration and both tracking methods are compared and combined for PMC.
FIDnavs and field probe navigators were implemented in a fast 3D-EPI sequence and calibrated by a linear model to realignment motion parameters of the 3D-EPI time series. A workflow was established to correct head motion prospectively by FIDnavs, field probe navigators or a combination of both. Large motions were instructed to test the accuracy and the impact on image quality in EPI data.
In a group of five subjects, FIDnavs demonstrated approximately doubled accuracy and precision in comparison with field probe navigators for large motions, especially nodding motions were tracked less accurately by field probes. A combination of both methods could not improve the accuracy consistently. Motion artifacts in high-resolution data were reduced similarly by both PMC methods, although artifacts remained due to susceptibility-induced B0 changes.
Stationary field probe navigators can be calibrated equivalently as FIDnavs and enable rapid PMC of large and fast motions. Although they reveal decreased accuracy, their contrast-independence facilitates the potential insertion into many sequences.
基于磁共振的自由感应衰减导航器（FIDnavs）不需要梯度脉冲，由于采集时间短和采样率高，对于前瞻性运动校正（PMC）具有吸引力。然而，其准确性和精确性有限，且依赖于单独的校准测量。除了FIDnavs，固定的核磁共振场探头也能够测量局部的、运动引起的场变化。在这项工作中，在场探头数据和类似于FIDnav校准的运动参数之间校准了一个线性模型，并将两种跟踪方法进行比较和组合用于PMC。
FIDnavs和场探头导航器在快速三维回波平面成像（3D-EPI）序列中实现，并通过线性模型校准以重新对齐3D-EPI时间序列的运动参数。建立了一个工作流程，以通过FIDnavs、场探头导航器或两者结合来前瞻性地校正头部运动。指导进行大幅度运动以测试EPI数据中的准确性以及对图像质量的影响。
在一组五名受试者中，对于大幅度运动，FIDnavs的准确性和精确性比场探头导航器提高了约一倍，特别是场探头对点头运动的跟踪不太准确。两种方法的组合并不能始终提高准确性。两种PMC方法对高分辨率数据中的运动伪影减少程度相似，尽管由于磁化率引起的B0变化仍存在伪影。
固定的场探头导航器可以与FIDnavs等效校准，并能够对大幅度和快速运动进行快速PMC。尽管它们的准确性有所降低，但其与对比度无关的特性便于将其潜在地插入到许多序列中。
