Hongyan He, Shufeng Wei, Huixian Wang, Wenhui Yang
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In the improved simulated annealing process, two swapping modes are presented, and randomly selected with certain probabilities that are set to 0.25, 0.5 and 0.75, respectively. The flexibility of the final designed structure is demonstrated by a spherical harmonic basis up to the full second order with single-target field control. An experimental platform is built to measure the gradient fields generated by the designed structure with multi-target target control.</p><h3 data-test=\"abstract-sub-heading\">Results</h3><p>With three probabilities of swapping modes, three similar coil element distributions are optimized, and their maximum magnetic field errors for generating <i>X</i>, <i>Y</i> and <i>Z</i> gradients are all below 5%. The structure selected for the final design is the one with a probability of 0.75, considering the coil performance and structural symmetry. The maximum error for all target fields generated by single-target field control is also below 5%. The experimental results show that the measured gradient fields along the axes have enough strength and high linearity.</p><h3 data-test=\"abstract-sub-heading\">Conclusions</h3><p>With the proposed improved simulated annealing algorithm and swapping modes, multi-target field control for matrix gradient coils is verified and achieved in this study by optimizing the coil element distribution. 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引用次数: 0
摘要
目的传统的矩阵梯度线圈单目标场控制会增加磁共振成像空间编码的控制复杂性,如设计专门的场和序列。方法基于多目标场控制原理,可将 X、Y 和 Z 梯度场设定为目标场,然后将所有线圈元件分为三组,以产生这些场。本文提出了一种改进的模拟退火算法,用于优化每组线圈元件的分布,以产生相应的目标场。在改进的模拟退火过程中,提出了两种交换模式,并以一定的概率随机选择,概率分别设置为 0.25、0.5 和 0.75。最终设计结构的灵活性通过球形谐波基达到全二阶单目标场控制得到了证明。建立了一个实验平台,用于测量设计结构在多目标控制下产生的梯度场。结果在三种交换模式概率下,优化了三种相似的线圈元件分布,其产生 X、Y 和 Z 梯度的最大磁场误差均低于 5%。考虑到线圈性能和结构对称性,最终设计选择了概率为 0.75 的结构。单目标场控制产生的所有目标场的最大误差也低于 5%。实验结果表明,测得的沿轴向梯度场具有足够的强度和较高的线性度。结论本研究利用提出的改进模拟退火算法和交换模式,通过优化线圈元件分布,验证并实现了矩阵梯度线圈的多目标场控制。此外,本研究还为简化空间编码中矩阵梯度线圈控制的复杂性提供了一种解决方案。
Multi-target field control for matrix gradient coils
Objective
Conventional single-target field control for matrix gradient coils will add control complexity in MRI spatial encoding, such as designing specialized fields and sequences. This complexity can be reduced by multi-target field control, which is realized by optimizing the coil structure according to target fields.
Methods
Based on the principle of multi-target field control, the X, Y and Z gradient fields can be set as target fields, and all coil elements can then be divided into three groups to generate these fields. An improved simulated annealing algorithm is proposed to optimize the coil element distribution of each group to generate the corresponding target field. In the improved simulated annealing process, two swapping modes are presented, and randomly selected with certain probabilities that are set to 0.25, 0.5 and 0.75, respectively. The flexibility of the final designed structure is demonstrated by a spherical harmonic basis up to the full second order with single-target field control. An experimental platform is built to measure the gradient fields generated by the designed structure with multi-target target control.
Results
With three probabilities of swapping modes, three similar coil element distributions are optimized, and their maximum magnetic field errors for generating X, Y and Z gradients are all below 5%. The structure selected for the final design is the one with a probability of 0.75, considering the coil performance and structural symmetry. The maximum error for all target fields generated by single-target field control is also below 5%. The experimental results show that the measured gradient fields along the axes have enough strength and high linearity.
Conclusions
With the proposed improved simulated annealing algorithm and swapping modes, multi-target field control for matrix gradient coils is verified and achieved in this study by optimizing the coil element distribution. Moreover, this study provides a solution to simplify the complexity of controlling the matrix gradient coil in spatial encoding.
期刊介绍:
MAGMA is a multidisciplinary international journal devoted to the publication of articles on all aspects of magnetic resonance techniques and their applications in medicine and biology. MAGMA currently publishes research papers, reviews, letters to the editor, and commentaries, six times a year. The subject areas covered by MAGMA include:
advances in materials, hardware and software in magnetic resonance technology,
new developments and results in research and practical applications of magnetic resonance imaging and spectroscopy related to biology and medicine,
study of animal models and intact cells using magnetic resonance,
reports of clinical trials on humans and clinical validation of magnetic resonance protocols.