A new computational tool for the analysis of Floor Borne Vibrations on the performance and image quality of MRI scanners

一种新的计算工具，用于分析地板振动对 MRI 扫描仪性能和图像质量的影响

• 批准号: 2600930
• 金额: --
• 依托单位: Swansea University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2600930
• 关键词: new; computational; tool; analysis; Floor

THE CONTEXTThe functioning of an MRI scanner relies on high strength and extremely uniform magnetic fields generated through superconducting magnets (i.e. main coils) and non-uniform magnetic fields generated by time-varying current signatures specified in AC gradient coils. A third key component in an MRI scanner is the cryostat, which is comprised of a series of radiation shields and keeps the main magnet coils immersed in liquid Helium within a Helium vessel. On the contrary, the gradient coils sit outside the cryostat at room temperature. Unfortunately, externally generated vibrations, also known as Floor Borne Vibrations (FBV), introduce undesirable accelerations on the magnets (primarily in the vertical direction, but also some in lateral direction). These vibrations can lead to relative movement between the radiation shields and the magnets, thus generating unwanted eddy currents in the shields which, in turn, produce secondary magnetic fields, the latter affecting the quality of the primary uniform magnetic field and, ultimately, resulting in non-desirable imaging artefacts.THE CHALLENGETo alleviate the negative impact of FBV, magnets are built with some amount of vibration isolation either underneath the cryostat, in the form of either a soft rubber matting or a spring-damper assembly, or by trial and error changes to the mechanical behaviour of the magnet and cryostat interface. However, the optimal design and the precise location of these vibration isolation devices within a realistic 3D MRI configuration is an extremely complex task which requires expert human intervention. The challenge at hand consists of predicting the performance of the MRI scanner over a wide range of input acceleration frequencies and determining the engineering changes required to reduce its sensitivity to FBV, via (a) the optimal selection of material parameters (i.e. shield conductivity, carbon fibre suspension stiffness) and (b) the shape optimisation of the MRI scanner components (i.e. flat or round ends in radiation shield components). This requires the a-priori (and very accurate) knowledge of the effect of FBV on: (a) the magnetic field distribution (i.e. to the Parts Per Billion level) and (b) the output image quality. This can only be achieved via cutting-edge high-fidelity in-silico modelling tools, robustly benchmarked against available experimental data, and embedded within the design cycle at Siemens Healthineers via the use of Reduced Order Modelling (ROM) techniques which can permit the rapid variation of material parameters and/or geometrical features.THE AIMThe development of a new robust, accurate and fast data-driven 3D in-silico ROM computational framework for the modelling of FBV on MRI performance and imaging quality. THE OBJECTIVESThe objectives of this challenging EPSRC CASE Award project proposal are four:1. The accurate computation of eddy currents and magnetic fields (i.e. to the Parts Per Billion level) within a realistic 3D MRI configuration when subjected to external FBV. The use of high order Finite Elements will be here exploited, investigating the order "p" of interpolation needed to produce the level of accuracy required. 2. The benchmarking of the software tool against experimental data collected from state-of-the-art shaker tables at Erlangen and Oxford. Experimental data will help ensure robustness and reliability of the software.3. The study of the impact of FBV on image quality through the combination of the developed software tool with in-house imaging analysis tools at Siemens Healthineers.4.The development of a ROM technique for fast multiple-query when considering the rapid variation of material parameters (i.e. stiffness, conductivity) and/or geometrical features (i.e. shield geometry). In-house experience at Siemens Healthineers will be here exploited in order to facilitate the identification of the most sensitive parameters to FBV.

MRI扫描仪的功能依赖于通过超导磁体（即主线圈）产生的高强度和极均匀的磁场以及由AC梯度线圈中指定的时变电流签名产生的非均匀磁场。MRI扫描仪的第三个关键部件是低温恒温器，它由一系列辐射屏蔽组成，并将主磁体线圈浸入氦容器内的液氦中。相反，梯度线圈在室温下位于低温恒温器外部。不幸的是，外部产生的振动，也称为地板振动（FBV），在磁体上引入不期望的加速度（主要在垂直方向上，但也有一些在横向方向上）。这些振动会导致辐射屏蔽和磁体之间的相对运动，从而在屏蔽中产生不需要的涡电流，这又产生次级磁场，次级磁场影响初级均匀磁场的质量，并最终导致不期望的成像伪影。磁体在低温恒温器下面以软橡胶垫或弹簧阻尼器组件的形式或者通过对磁体和低温恒温器界面的机械行为的试验和错误改变来构建有一定量的振动隔离。然而，这些隔振装置在真实3D MRI配置中的最佳设计和精确位置是一项极其复杂的任务，需要专家人工干预。目前的挑战包括预测MRI扫描仪在宽范围的输入加速度频率下的性能，并确定降低其对FBV的敏感性所需的工程更改，通过（a）材料参数的最佳选择（即屏蔽电导率，碳纤维悬挂刚度）和（B）MRI扫描仪部件的形状优化（即，辐射屏蔽部件中的平端或圆端）。这需要先验（并且非常准确）地了解FBV对以下各项的影响：（a）磁场分布（即，达到十亿分之一水平）和（B）输出图像质量。这只能通过尖端的高保真计算机模拟建模工具来实现，该工具以可用的实验数据为基准，并通过使用降阶建模（ROM）技术嵌入到西门子医疗的设计周期中，该技术可以允许材料参数和/或几何特征的快速变化。准确和快速的数据驱动的3D计算机ROM计算框架，用于对MRI性能和成像质量进行FBV建模。这个具有挑战性的EPSRC案例奖项目提案的目标是四个：1。当受到外部FBV时，在真实的3D MRI配置内准确计算涡流和磁场（即达到十亿分之一水平）。这里将利用高阶有限元的使用，研究产生所需准确度所需的插值阶数“p”。2.该软件工具的基准测试是根据从埃尔兰根和牛津最先进的振动台收集的实验数据进行的。实验数据将有助于确保软件的鲁棒性和可靠性.通过将开发的软件工具与Siemens Healthineers的内部成像分析工具相结合，研究FBV对图像质量的影响。4.在考虑材料参数（即刚度、电导率）和/或几何特征（即屏蔽几何形状）的快速变化时，开发用于快速多重查询的ROM技术。在此，将利用西门子医疗公司的内部经验，以促进对FBV最敏感参数的识别。