Permanent magnet for "gradient-free" MRI

MRI是一种完善的非侵入性诊断技术，在大多数现代医院中使用，可提供高质量的全身图像。然而，有一些缺陷阻碍了这种有价值的技术的更快发展和更广泛的应用。其中包括成本高，磁铁的幽闭几何形状以及需要特殊场地准备的巨大重量。我们建议通过设计和构建一种紧凑的轻质磁铁来解决这些弱点，这种磁铁专门用于“无梯度”MRI技术，称为TRASE。标准的MRI需要随时间变化的强磁场梯度，而在申请人参与下开发的TRASE技术，使用射频（RF）场代替磁场梯度的空间编码，从而消除了磁场梯度组件，即目前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，有可能生产廉价、轻便和静音的核磁共振成像系统，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MR图像。我们现在建议设计和构建一个轻型的“切片选择”磁铁，包括3个同轴环，在一个狭窄的圆柱体内产生均匀的磁场，允许使用非选择性射频脉冲进行切片选择。这种设计将允许在一个方向上进行切片选择，并在垂直平面上进行二维TRASE。磁体的设计是遗传算法应用于磁体结构，TRASE开发和我们独特的磁体设计的结果。为了设计磁体，我们将使用Opera 3D软件进行有限元分析。Matlab脚本将提供将通过通用算法优化的磁铁几何形状和块规格。这些数据将被传输到Opera计算场分布，并为后续迭代提供反馈给Matlab。目前标准的核磁共振磁铁重达数千公斤，而用于人体手腕成像的新型磁铁的估计重量为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。磁性块将从中国纽兰购买。磁体的均匀性将通过连接在自动机械臂上的3D霍尔探头在圆柱体上测量，并使用圆柱体谐波进行分析。磁场不均匀性将通过校正磁块的位置和使用小型补偿磁体进行微调来最小化，从而使磁场的均匀性和分布达到目标值。该磁体将允许在我们的实验室建造光TRASE MRI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.