Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, USA.
Sci Rep. 2024 Feb 8;14(1):3307. doi: 10.1038/s41598-024-53703-y.
Eliminating conventional pulsed B-gradient coils for magnetic resonance imaging (MRI) can significantly reduce the cost of and increase access to these devices. Phase shifts induced by the Bloch-Siegert shift effect have been proposed as a means for gradient-free, RF spatial encoding for low-field MR imaging. However, nonlinear phasor patterns like those generated from loop coils have not been systematically studied in the context of 2D spatial encoding. This work presents an optimization algorithm to select an efficient encoding trajectory among the nonlinear patterns achievable with a given hardware setup. Performance of encoding trajectories or projections was evaluated through simulated and experimental image reconstructions. Results show that the encodings schemes designed by this algorithm provide more efficient spatial encoding than comparison encoding sets, and the method produces images with the predicted spatial resolution and minimal artifacts. Overall, the work demonstrates the feasibility of performing 2D gradient-free, low-field imaging using the Bloch-Siegert shift which is an important step towards creating low-cost, point-of-care MR systems.
消除磁共振成像（MRI）中的传统脉冲梯度线圈可以显著降低这些设备的成本并增加其可及性。Bloch-Siegert 位移效应引起的相位偏移已被提议作为一种用于低磁场磁共振成像的无梯度、RF 空间编码方法。然而，像来自环形线圈那样的非线性相量模式尚未在二维空间编码的背景下得到系统研究。本工作提出了一种优化算法，用于在给定的硬件设置下从可实现的非线性模式中选择有效的编码轨迹。通过模拟和实验图像重建来评估编码轨迹或投影的性能。结果表明，通过该算法设计的编码方案比比较编码集提供了更有效的空间编码，并且该方法生成的图像具有预测的空间分辨率和最小的伪影。总体而言，这项工作证明了使用 Bloch-Siegert 位移进行二维无梯度、低磁场成像的可行性，这是朝着创建低成本、即时护理磁共振系统迈出的重要一步。
