Computational Radiology Laboratory, Department of Radiology, Boston Children's Hospital, Boston, Massachusetts, USA.
Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA.
Magn Reson Med. 2022 Dec;88(6):2548-2563. doi: 10.1002/mrm.29421. Epub 2022 Sep 12.
To implement a method for real-time field control using rapid FID navigator (FIDnav) measurements and evaluate the efficacy of the proposed approach for mitigating dynamic field perturbations and improving -weighted image quality.
FIDnavs were embedded in a gradient echo sequence and a subject-specific linear calibration model was generated on the scanner to facilitate rapid shim updates in response to measured FIDnav signals. To confirm the accuracy of FID-navigated field updates, phantom and volunteer scans were performed with online updates of the scanner B shim settings. To evaluate improvement in -weighted image quality with real-time shimming, 10 volunteers were scanned at 3T while performing deep-breathing and nose-touching tasks designed to modulate the B field. Quantitative image quality metrics were compared with and without FID-navigated field control. An additional volunteer was scanned at 7T to evaluate performance at ultra-high field.
Applying measured FIDnav shim updates successfully compensated for applied global and linear field offsets in phantoms and across all volunteers. FID-navigated real-time shimming led to a substantial reduction in field fluctuations and a consequent improvement in -weighted image quality in volunteers performing deep-breathing and nose-touching tasks, with 7.57% ± 6.01% and 8.21% ± 10.90% improvement in peak SNR and structural similarity, respectively.
FIDnavs facilitate rapid measurement and application of field coefficients for slice-wise B shimming. The proposed approach can successfully counteract spatiotemporal field perturbations and substantially improves -weighted image quality, which is important for a variety of clinical and research applications, particularly at ultra-high field.
实现一种使用快速 FID 导航器（FIDnav）测量进行实时现场控制的方法，并评估该方法在减轻动态场干扰和改善加权图像质量方面的效果。
在梯度回波序列中嵌入 FIDnav，并在扫描仪上生成特定于受试者的线性校准模型，以方便根据测量的 FIDnav 信号快速更新 shim。为了确认 FID 导航场更新的准确性，在线更新扫描仪 B shim 设置进行了幻影和志愿者扫描。为了评估实时调谐对加权图像质量的改善，在 3T 下对 10 名志愿者进行扫描，同时执行旨在调制 B 场的深呼吸和触摸鼻子任务。比较了有无 FID 导航场控制的定量图像质量指标。另外，对一名志愿者在 7T 下进行了扫描，以评估超高场的性能。
应用测量的 FIDnav shim 更新成功补偿了幻影和所有志愿者中的全局和线性场偏移。FID 导航实时调谐导致场波动大幅减少，志愿者在执行深呼吸和触摸鼻子任务时的加权图像质量得到显著改善，峰值信噪比和结构相似性分别提高了 7.57%±6.01%和 8.21%±10.90%。
FIDnav 有助于快速测量和应用切片式 B shim 的场系数。该方法可以成功地抵消时空场干扰，并显著改善加权图像质量，这对于各种临床和研究应用都很重要，特别是在超高场。
