Shahryari Mehrgan, Meyer Tom, Warmuth Carsten, Herthum Helge, Bertalan Gergely, Tzschätzsch Heiko, Stencel Lisa, Lukas Steffen, Lilaj Ledia, Braun Jürgen, Sack Ingolf
Department of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Institute of Medical Informatics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Magn Reson Med. 2021 Apr;85(4):1962-1973. doi: 10.1002/mrm.28558. Epub 2020 Oct 26.
With abdominal magnetic resonance elastography (MRE) often suffering from breathing artifacts, it is recommended to perform MRE during breath-hold. However, breath-hold acquisition prohibits extended multifrequency MRE examinations and yields inconsistent results when patients cannot hold their breath. The purpose of this work was to analyze free-breathing strategies in multifrequency MRE of abdominal organs.
Abdominal MRE with 30, 40, 50, and 60 Hz vibration frequencies and single-shot, multislice, full wave-field acquisition was performed four times in 11 healthy volunteers: once with multiple breath-holds and three times during free breathing with ungated, gated, and navigated slice adjustment. Shear wave speed maps were generated by tomoelastography inversion. Image registration was applied for correction of intrascan misregistration of image slices. Sharpness of features was quantified by the variance of the Laplacian.
Total scan times ranged from 120 seconds for ungated free-breathing MRE to 376 seconds for breath-hold examinations. As expected, free-breathing MRE resulted in larger organ displacements (liver, 4.7 ± 1.5 mm; kidneys, 2.4 ± 2.2 mm; spleen, 3.1 ± 2.4 mm; pancreas, 3.4 ± 1.4 mm) than breath-hold MRE (liver, 0.7 ± 0.2 mm; kidneys, 0.4 ± 0.2 mm; spleen, 0.5 ± 0.2 mm; pancreas, 0.7 ± 0.5 mm). Nonetheless, breathing-related displacement did not affect mean shear wave speed, which was consistent across all protocols (liver, 1.43 ± 0.07 m/s; kidneys, 2.35 ± 0.21 m/s; spleen, 2.02 ± 0.15 m/s; pancreas, 1.39 ± 0.15 m/s). Image registration before inversion improved the quality of free-breathing examinations, yielding no differences in image sharpness to uncorrected breath-hold MRE in most organs (P > .05).
Overall, multifrequency MRE is robust to breathing when considering whole-organ values. Respiration-related blurring can readily be corrected using image registration. Consequently, ungated free-breathing MRE combined with image registration is recommended for multifrequency MRE of abdominal organs.
腹部磁共振弹性成像（MRE）常受呼吸伪影影响，因此建议在屏气期间进行MRE检查。然而，屏气采集限制了多频率MRE检查的时间，并且当患者无法屏气时会产生不一致的结果。本研究旨在分析腹部器官多频率MRE的自由呼吸策略。
对11名健康志愿者进行了4次腹部MRE检查，振动频率分别为30、40、50和60Hz，采用单次激发、多层、全波场采集：一次屏气采集，三次自由呼吸采集，分别采用非门控、门控和导航切片调整。通过弹性成像反演生成剪切波速度图。应用图像配准来校正图像切片的扫描内配准误差。通过拉普拉斯方差对特征锐度进行量化。
总扫描时间范围从非门控自由呼吸MRE的120秒到屏气检查的376秒。正如预期的那样，自由呼吸MRE导致的器官位移（肝脏，4.7±1.5mm；肾脏，2.4±2.2mm；脾脏，3.1±2.4mm；胰腺，3.4±1.4mm）比屏气MRE（肝脏，0.7±0.2mm；肾脏，0.4±0.2mm；脾脏，0.5±0.2mm；胰腺，0.7±0.5mm）更大。尽管如此，呼吸相关位移并未影响平均剪切波速度，所有方案中的平均剪切波速度均一致（肝脏，1.43±0.07m/s；肾脏，2.35±0.21m/s；脾脏，2.02±0.15m/s；胰腺，1.39±0.15m/s）。反演前的图像配准提高了自由呼吸检查的质量，在大多数器官中，图像锐度与未校正的屏气MRE无差异（P>.05）。
总体而言，在考虑全器官值时，多频率MRE对呼吸具有鲁棒性。呼吸相关的模糊可以通过图像配准轻松校正。因此，对于腹部器官的多频率MRE，建议采用非门控自由呼吸MRE并结合图像配准。
