The design of a light and compact magnet for MRI

一种轻便紧凑的MRI磁体的设计

• 批准号: RGPIN-2015-03992
• 负责人: Tomanek, Boguslaw
• 金额: $ 2.33万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=666944
• 关键词: design; light; compact; magnet; MRI

MRI is the best non-invasive diagnostic imaging modality providing high quality images of the entire body. However, its high costs and claustrophobic magnet geometry prevent a faster growth and broader applications. Therefore we propose to address these weaknesses by designing a new magnet suitable for MRI based on the so-called Halbach structure.****Halbach magnets have a cylindrical shape and comprise small magnetic pieces placed on a surface of a cylinder. Although the Halbach design has been known for over 30 years, a full analytical theory of the magnetic field produced by the magnet has been developed only for a very high length/diameter ratio, when the mathematical description of the field can be reduced to two dimensions (2D). A 3D mathematical model of the finite-length magnet ("long" magnet) with small length/diameter ratio (<1) has been proposed very recently (2014) but a magnet based on this theory has not yet been constructed. Computer programs solving semi-analytical field equations, using the finite elements or the boundary methods to calculate the field have been developed yet not without drawbacks. Furthermore magnet weight or its size have not been optimized so far. In addition, there is no perfect manufacturing process, yet none of the theoretical models include manufacturing errors, such as inconsistent segmentation of the magnetic pieces over the cylinder's surface or their imperfect position.****It is known that, for example, 2D segmentation causes creation of harmonics of the order of a multiple of the number of the segments. To deal with this common problem, the magnetic field over a sphere is analyzed using spherical harmonics. From this analysis, the placement of small compensating magnets is calculated to cancel the spherical harmonics and to improve magnet homogeneity. The field homogeneity may be also improved by correcting positions of the segments. However none of these methods is perfect. In our approach we propose to develop a method of shimming on a surface of a cylinder instead of a sphere, as traditionally used. We expect this approach will provide efficient shimming for "short" Halbach magnets.****In summary, we propose to develop a new design of a light, permanent magnet suitable for standard and "gradient free" MRI, co-developed by the applicant. As "gradient free" MRI does not require gradients of the magnetic field and associated amplifiers, it is feasible to produce inexpensive, light and silent MRI system for many new imaging applications.******

MRI是最好的无创诊断成像方式，可提供全身的高质量图像。然而，它的高成本和幽闭的磁铁几何形状阻碍了更快的增长和更广泛的应用。因此，我们建议通过设计一种基于所谓的Halbach结构的适合MRI的新磁铁来解决这些弱点。****哈尔巴赫磁铁具有圆柱形，由放置在圆柱体表面的小磁性块组成。虽然哈尔巴赫的设计已经有30多年的历史了，但磁铁产生的磁场的完整分析理论只适用于非常高的长度/直径比，当磁场的数学描述可以减少到二维（2D）时。最近（2014年）提出了小长径比（<1）的有限长度磁铁（“长”磁铁）的三维数学模型，但基于该理论的磁铁尚未构建。利用有限元或边界法求解半解析场方程的计算机程序已经开发出来，但并非没有缺陷。此外，磁铁的重量和尺寸到目前为止还没有得到优化。此外，没有完美的制造工艺，但没有一个理论模型包括制造误差，如磁片在圆柱体表面的分割不一致或它们的位置不完美。****众所周知，例如，二维分割会产生数倍于分割段数的谐波。为了解决这个常见的问题，用球谐波分析了球上的磁场。在此基础上，计算了小型补偿磁体的位置，以消除球面谐波，改善磁体的均匀性。还可以通过校正片段的位置来改善场的均匀性。然而，这些方法都不是完美的。在我们的方法中，我们建议开发一种在圆柱体表面而不是传统上使用的球体表面上进行摆光的方法。我们期望这种方法将为“短”哈尔巴赫磁体提供有效的摆振。****总之，我们建议开发一种适合标准和“无梯度”MRI的轻型永磁体的新设计，由申请人共同开发。由于“无梯度”MRI不需要磁场梯度和相关放大器，因此可以为许多新的成像应用生产廉价，轻便和静音的MRI系统。******