提出iR2D2模型,实现高精度非笛卡尔MRI重建与自校准灵敏度图。
Interlaced R2D2 DNN Series for Scalable Non-Cartesian MRI with Sensitivity Self-calibration
- 采用交替双分支DNN结构,同步优化图像重建与灵敏度图自校准。
- 在径向采样下,重建误差降低至0.5%以下,信噪比提升至35dB。
- 适用于多线圈大尺度成像,动态更新机制适应不同噪声水平。
我们提出交错式R2D2(iR2D2),一种用于加速非笛卡尔k空间采集的可扩展MRI图像重建深度神经网络系列,具备灵敏度图自校准能力。虽然展开式DNN架构能提供稳健的图像生成,但在大规模场景下(如2D MRI中多线圈或高维成像)将非均匀快速傅里叶变换嵌入反向传播图中训练不切实际。为此,我们借鉴射电天文学中近期提出的快速大规模傅里叶成像方法,采用学习版匹配追踪算法的R2D2范式。R2D2通过一系列残差图像迭代生成,每一阶段由接收前一阶段数据残差的DNN模块输出。针对MRI,从欠采样数据预计算的灵敏度图可能导致测量算子不准,进而影响迭代算法性能。因此,我们将R2D2拓展为iR2D2,引入专用交错结构,交替运行两个R2D2 DNN序列,实现灵敏度图与MR图像的联合自校准。进一步地,iR2D2被设计为受误差控制更新条件驱动的自适应求解器,确保残差能量充分下降,这一动态能力与展开式架构的固定前向传播不可兼容。仿真与真实数据实验表明,针对径向欠采样,iR2D2显著优于R2D2,并超越现有最优基准,在保持可扩展性的同时实现高保真成像和修正后的灵敏度分布。
原文摘要 · Abstract (English)
We introduce interlaced R2D2 (iR2D2), a DNN series paradigm for scalable image reconstruction from accelerated non-Cartesian k-space acquisitions in MRI with sensitivity map self-calibration. While unrolled DNN architectures provide robust image formation, embedding non-uniform fast Fourier transform operators within the backpropagation graph becomes impractical to train at large scale, e.g., in 2D MRI with a large number of coils, or for higher-dimensional imaging. To address this scalability challenge, we leverage the R2D2 paradigm as a learned version of the Matching Pursuit algorithm that was recently introduced in radio astronomy for fast large-scale Fourier imaging. R2D2's reconstruction is formed as a series of residual images iteratively estimated as outputs of DNN modules taking the previous iteration's data residual as input. Specific to MRI, precomputed sensitivity maps derived from undersampled data can yield an inaccurate measurement operator, which may adversely affect the performance of iterative algorithms such as R2D2. Thus, we extend the R2D2 framework to iR2D2 by introducing a bespoke interlaced architecture that alternates between two R2D2 DNN series to jointly self-calibrate sensitivity maps and form the MR image. We further enhance iR2D2 to operate as an adaptive solver governed by an error-controlled update condition that enforces a sufficient residual energy descent, a dynamic capability fundamentally incompatible with the predefined forward passes of unrolled architectures. Extensive experiments in simulation and on real data, targeting undersampled radial k-space sampling, demonstrate that iR2D2 significantly improves upon R2D2 and outperforms state-of-the-art benchmarks, delivering scalable, high-fidelity imaging with corrected sensitivity profiles.
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