Ying Leslie, Sheng Jinhua
Department of Electrical Engineering and Computer Science, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
Magn Reson Med. 2007 Jun;57(6):1196-202. doi: 10.1002/mrm.21245.
Parallel magnetic resonance imaging (pMRI) using multichannel receiver coils has emerged as an effective tool to reduce imaging time in various applications. However, the issue of accurate estimation of coil sensitivities has not been fully addressed, which limits the level of speed enhancement achievable with the technology. The self-calibrating (SC) technique for sensitivity extraction has been well accepted, especially for dynamic imaging, and complements the common calibration technique that uses a separate scan. However, the existing method to extract the sensitivity information from the SC data is not accurate enough when the number of data is small, and thus erroneous sensitivities affect the reconstruction quality when they are directly applied to the reconstruction equation. This paper considers this problem of error propagation in the sequential procedure of sensitivity estimation followed by image reconstruction in existing methods, such as sensitivity encoding (SENSE) and simultaneous acquisition of spatial harmonics (SMASH), and reformulates the image reconstruction problem as a joint estimation of the coil sensitivities and the desired image, which is solved by an iterative optimization algorithm. The proposed method was tested on various data sets. The results from a set of in vivo data are shown to demonstrate the effectiveness of the proposed method, especially when a rather large net acceleration factor is used.
使用多通道接收线圈的并行磁共振成像（pMRI）已成为在各种应用中减少成像时间的有效工具。然而，线圈灵敏度的准确估计问题尚未得到充分解决，这限制了该技术可实现的加速水平。用于灵敏度提取的自校准（SC）技术已被广泛接受，特别是对于动态成像，并且补充了使用单独扫描的常规校准技术。然而，当数据数量较少时，从SC数据中提取灵敏度信息的现有方法不够准确，因此错误的灵敏度直接应用于重建方程时会影响重建质量。本文考虑了现有方法（如灵敏度编码（SENSE）和空间谐波同时采集（SMASH））在灵敏度估计后续图像重建的顺序过程中的误差传播问题，并将图像重建问题重新表述为线圈灵敏度和所需图像的联合估计，通过迭代优化算法求解。所提出的方法在各种数据集上进行了测试。一组体内数据的结果表明了所提出方法的有效性，特别是在使用相当大的净加速因子时。
