Permanent magnet for "gradient-free" MRI

核磁共振成像是一种成熟的非侵入性诊断技术，用于大多数现代医院，提供高质量的全身图像。然而，还有一些不足之处阻碍了这项宝贵技术的更快增长和更广泛的应用。其中包括成本高、磁铁的幽闭几何形状以及它的巨大重量需要特殊的场地准备。我们建议通过设计和建造一种紧凑、轻便的磁体来解决这些弱点，该磁体专门用于名为TRASE的“无梯度”磁共振技术。虽然标准MRI需要随时间变化的强磁场梯度，但在申请人的参与下开发的TRASE技术将使用磁场梯度的空间编码替换为射频(RF)场，从而消除了磁场梯度分量，即当前MRI系统中使用的梯度线圈和放大器。TRASE技术还降低了对磁场的高均匀性要求。因此，有可能生产价格低廉、重量轻、静音的MRI系统，这些系统可以广泛使用，并用于新的成像应用。我们已经使用目前可用的磁铁收集了磁共振图像。我们现在建议设计和建造一种轻型的“切片选择”磁体，它由3个同轴磁环组成，在一个狭窄的圆柱体内产生均匀的磁场，从而允许使用非选择性RF脉冲进行切片选择。这种设计将允许在一个方向上选择切片，并在垂直平面上选择2D TRASE。磁铁的设计是遗传算法在磁铁结构中应用的进步、TRASE的开发以及我们独特的磁铁设计的结果。为了设计磁体，我们将使用OPERA 3D软件进行有限元分析。一个Matlab脚本将提供磁铁几何和块规格，将通过通用算法进行优化。这些数据将被传输到OPERA来计算场分布，并为后续迭代向MatLab提供反馈。尽管目前标准的核磁共振磁铁重达数千公斤，但用于人体手腕成像的新磁铁的估计重量为10公斤。我们打算使用现有的3D打印机来制造磁性块的支撑。磁块将从纽兰购买，中国。磁铁的均匀性将在圆柱体上使用连接到自动化机械臂上的3D霍尔探头进行测量，并使用柱面谐波进行分析。通过校正磁块的位置和使用小补偿磁铁进行精细匀场，以使磁场的均匀和分布达到目标值，将使磁场不均匀最小化。这块磁铁将允许在我们的实验室建造轻型TRASE核磁共振系统的原型。

MRI is a well-established non-invasive diagnostic technique used in most modern hospitals that provides high quality images of the entire body. However, there are deficiencies that prevent faster growth and broader application of this valuable technique. Among them are high costs, claustrophobic geometry of the magnet and its substantial weight requiring special site preparation. We propose to address these weaknesses by designing and constructing a compact lightweight magnet specifically for the "gradient free" MRI technique called TRASE. While standard MRI requires time-variable strong gradients of the magnetic field, the TRASE technique, developed with the participation of the applicant, replaces spatial encoding using gradients of the magnetic field with the radiofrequency (RF) field, thus eliminating the magnetic field gradient components, namely the gradient coils and amplifiers used in current MRI systems. The TRASE technique also lessens the high homogeneity requirement for the magnetic field. It is therefore possible to produce inexpensive, light and silent MRI systems that can be made broadly available and used for new imaging applications. We have already collected MR images using magnets that are currently available. We now propose to design and construct a light, "slice selective" magnet comprising 3 coaxial rings that generate a homogenous magnetic field within a narrow cylinder which allows slice selection using non-selective RF pulses. This design will allow slice selection in one direction and 2D TRASE in the perpendicular plane. The design of the magnet is the result of advances in application of genetic algorithms to magnets construction, development of TRASE and our unique magnet design. To design the magnet, we will use Opera 3D software which performs finite element analysis. A Matlab script will provide magnet geometries and block specifications that will be optimized by generic algorithm. This data will be transferred to Opera to calculate the field distribution and provide feedback to Matlab for the subsequent iterations. Whereas current standard MRI magnets weigh thousands of kilograms, the estimated weight of the new magnet for imaging of the human wrist is 10kg. We intend to use an existing 3D printer to fabricate support for the magnetic blocks. The magnetic blocks will be purchased from Newland, China. The homogeneity of the magnet will be measured over a cylinder using a 3D Hall probe attached to an automated robotic arm and analyzed using cylindrical harmonics. Field inhomogeneities will be minimized by correcting the positions of the magnetic blocks and by fine shimming using small compensating magnets to bring homogeneity and distribution of the magnetic field to the target value. The magnet will allow construction of a prototype of the light TRASE MRI system in our laboratory.