Mekle Ralf, Laine Andrew F, Wu Ed X
Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA.
IEEE Trans Med Imaging. 2003 Jul;22(7):806-23. doi: 10.1109/TMI.2003.815054.
A new technique to reduce clinical magnetic resonance imaging (MRI) scan time by varying acquisition parameters and sharing k-space data between images, is proposed. To improve data utilization, acquisition of multiple images of different contrast is combined into a single scan, with variable acquisition parameters including repetition time (TR), echo time (TE), and echo train length (ETL). This approach is thus referred to as a "combo acquisition." As a proof of concept, simulations of MRI experiments using spin echo (SE) and fast SE (FSE) sequences were performed based on Bloch equations. Predicted scan time reductions of 25%-50% were achieved for 2-contrast and 3-contrast combo acquisitions. Artifacts caused by nonuniform k-space data weighting were suppressed through semi-empirical optimization of parameter variation schemes and the phase encoding order. Optimization was assessed by minimizing three quantitative criteria: energy of the "residue point spread function (PSF)," energy of "residue profiles" across sharp tissue boundaries, and energy of "residue images." In addition, results were further evaluated by quantitatively analyzing the preservation of contrast, the PSF, and the signal-to-noise ratio. Finally, conspicuity of lesions was investigated for combo acquisitions in comparison with standard scans. Implications and challenges for the practical use of combo acquisitions are discussed.
本文提出了一种通过改变采集参数并在图像之间共享k空间数据来减少临床磁共振成像（MRI）扫描时间的新技术。为了提高数据利用率，将不同对比度的多个图像采集合并为一次扫描，采用包括重复时间（TR）、回波时间（TE）和回波链长度（ETL）在内的可变采集参数。因此，这种方法被称为“组合采集”。作为概念验证，基于布洛赫方程对使用自旋回波（SE）和快速SE（FSE）序列的MRI实验进行了模拟。对于2对比度和3对比度组合采集，预测扫描时间减少了25%-50%。通过对参数变化方案和相位编码顺序进行半经验优化，抑制了由非均匀k空间数据加权引起的伪影。通过最小化三个定量标准来评估优化效果：“残留点扩散函数（PSF）”的能量、跨锐利组织边界的“残留轮廓”的能量以及“残留图像”的能量。此外，通过定量分析对比度、PSF和信噪比的保留情况进一步评估结果。最后，与标准扫描相比，研究了组合采集时病变的可见性。讨论了组合采集实际应用中的意义和挑战。
