arXiv:2501.12157cs.CV2025-01被引 1

用深度学习提速7T MRI射频匀场,快5000倍且更准。

Fast-RF-Shimming: Accelerate RF Shimming in 7T MRI using Deep Learning

  • 用ResNet直接从射频场预测匀场参数,省去传统优化迭代。
  • 相比传统方法快5000倍,且预测精度更高。
  • 适合需要快速成像的临床与高场科研场景。

超高场磁共振成像(UHF MRI)虽能提供更高的信噪比和空间分辨率,但随之而来的射频场(B₁⁺)不均匀性会导致翻转角失真和图像强度不均,影响图像质量并阻碍临床应用。传统射频匀场方法如幅度最小二乘法(MLS)虽有效,但耗时过长。现有机器学习方法存在训练时间长、网络复杂度低等问题。本文提出Fast-RF-Shimming框架:首先用随机初始化的Adam优化获得参考匀场权重;再训练残差网络(ResNet)将多通道B₁⁺场直接映射为最优射频匀场输出,并在损失函数中引入置信度参数;最后设计非均匀场检测器(NFD)作为可选后处理步骤,识别极端非均匀情况。对比实验表明,该方法相较传统MLS实现5000倍加速,同时保持更高预测精度,为解决7T MRI中的长期不均匀性问题提供了可行方案。

原文摘要 · Abstract (English)

Ultrahigh field (UHF) Magnetic Resonance Imaging (MRI) offers an elevated signal-to-noise ratio (SNR), enabling exceptionally high spatial resolution that benefits both clinical diagnostics and advanced research. However, the jump to higher fields introduces complications, particularly transmit radiofrequency (RF) field ($B_{1}^{+}$) inhomogeneities, manifesting as uneven flip angles and image intensity irregularities. These artifacts can degrade image quality and impede broader clinical adoption. Traditional RF shimming methods, such as Magnitude Least Squares (MLS) optimization, effectively mitigate $B_{1}^{+}$ inhomogeneity, but remain time-consuming. Recent machine learning approaches, including RF Shim Prediction by Iteratively Projected Ridge Regression and other deep learning architectures, suggest alternative pathways. Although these approaches show promise, challenges such as extensive training periods, limited network complexity, and practical data requirements persist. In this paper, we introduce a holistic learning-based framework called Fast-RF-Shimming, which achieves a 5000x speed-up compared to the traditional MLS method. In the initial phase, we employ random-initialized Adaptive Moment Estimation (Adam) to derive the desired reference shimming weights from multi-channel $B_{1}^{+}$ fields. Next, we train a Residual Network (ResNet) to map $B_{1}^{+}$ fields directly to the ultimate RF shimming outputs, incorporating the confidence parameter into its loss function. Finally, we design Non-uniformity Field Detector (NFD), an optional post-processing step, to ensure the extreme non-uniform outcomes are identified. Comparative evaluations with standard MLS optimization underscore notable gains in both processing speed and predictive accuracy, which indicates that our technique shows a promising solution for addressing persistent inhomogeneity challenges.

MRI射频匀场深度学习加速

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