MAGNETIC RESONANCE IMAGING OF MOVING PATIENTS AT ULTRA-HIGH FIELD: REAL-TIME MOTION CORRECTED PARALLEL-TRANSMIT PULSE DESIGN

超高场移动患者的磁共振成像：实时运动校正并行传输脉冲设计

• 批准号: 2218828
• 金额: --
• 依托单位: CARDIFF UNIVERSITY
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2218828
• 关键词: MAGNETIC; RESONANCE; IMAGING; MOVING; PATIENTS

Ultra-high field (UHF, 7T and above) magnetic resonance imaging (MRI) scanners present a unique opportunity to study the brain at much higher resolution than previously possible. Many brain MRI acquisitions last upwards of several minutes. Any small deviation in subject position during this time, due to involuntary movement or breathing, can change the imaged volume, leading to destructive artefacts in the images, and necessitating a rescan of the patient. Additionally, questions arise regarding patient safety, as effects of motion on the small amounts of tissue heating which occur during MRI are not well understood. Motion is specifically problematic with uncooperative patients such as in paediatric imaging, or for patients with Parkinson's or dementia. Sedation, which is common practice in such cases, is invasive, affects results obtained for non-structural MRI techniques (e.g. functional MRI), and has been reported to cause adverse side effects and even admittance to emergency care. To overcome electromagnetic interference at UHF, parallel transmission (pTx) hardware can be used, significantly improving image quality and control over tissue heating. pTx allows radiofrequency (RF) pulses -used to generate the MRI signal- to be delivered by multiple, independently controlled RF channels. However, the benefits of pTx come at a cost of exacerbating the motion-related problems described above, as the channels' RF interacts in complex ways. The extra degrees of freedom offered by pTx (i.e. because the channels are independently controlled) mean that the problem could be overcome with a new approach to pTx RF pulse design, given a more comprehensive understanding of the interactions between channels under conditions of motion, and application of that to the RF pulse design process.My research approaches this problem in two ways. Firstly, I am developing a motion-robust approach to pTx pulse design. Using computer simulations, I initially investigated the effects of motion in different pTx contexts to better understand the dynamics involved. Following this, I devised a new approach which has reduced the sensitivity of pTx pulses to motion in simulations, meaning that image quality remains high even in the case of patient motion. My immediate next steps are to continue simulations to ensure that the safety (tissue heating) issue also benefits from my approach, and validate the approach using scanner experiments. Beyond reducing sensitivity by introducing motion-robustness, a second focus of my research contributes towards a real-time pTx pulse design method. This would allow real-time updates to be applied to the scanner, compensating for patient motion as it occurs throughout the scan, and therefore more accurately and effectively negating all motion-induced effects. I am using a machine learning approach to train a neural network with simulated training data for development of the approach, before testing on experiments. Implications of my work are widespread. By removing motion-related concerns over pTx, the benefits of UHF MRI (e.g. the higher image resolution) can be applied clinically. Areas such as epilepsy and MS diagnosis and prognosis have already demonstrated benefits of this in research contexts, but the technical challenges mentioned here currently prevent its widespread or clinical use

超高场（UHF，7 T及以上）磁共振成像（MRI）扫描仪提供了一个独特的机会，以比以前更高的分辨率研究大脑。许多脑部MRI采集持续数分钟以上。在此期间，由于无意识运动或呼吸，受试者位置的任何小偏差都可能改变成像体积，导致图像中的破坏性伪影，并需要重新扫描患者。此外，还出现了关于患者安全的问题，因为对MRI期间发生的少量组织加热的运动影响尚未充分了解。对于不合作的患者，例如在儿科成像中，或者对于帕金森氏症或痴呆症患者，运动是特别有问题的。镇静，这是在这种情况下的常见做法，是侵入性的，影响非结构性MRI技术（如功能性MRI）获得的结果，并已报告导致不良副作用，甚至进入急诊室。为了克服UHF下的电磁干扰，可以使用并行传输（pTx）硬件，从而显著提高图像质量和对组织加热的控制。pTx允许射频（RF）脉冲-用于生成MRI信号-由多个独立控制的RF通道输送。然而，pTx的好处是以加剧上述运动相关问题为代价的，因为通道的RF以复杂的方式相互作用。pTx提供的额外自由度（即因为通道是独立控制的）意味着，如果对运动条件下通道之间的相互作用有更全面的了解，并将其应用于RF脉冲设计过程，则可以通过pTx RF脉冲设计的新方法来克服这个问题。我的研究从两个方面解决这个问题。首先，我正在开发一种运动鲁棒的pTx脉冲设计方法。使用计算机模拟，我最初研究了不同pTx背景下运动的影响，以更好地理解所涉及的动态。在此之后，我设计了一种新方法，该方法降低了pTx脉冲对模拟中运动的敏感性，这意味着即使在患者运动的情况下，图像质量也保持较高。我的下一步是继续模拟，以确保安全（组织加热）问题也受益于我的方法，并使用扫描仪实验验证该方法。除了通过引入运动鲁棒性来降低灵敏度之外，我的研究的第二个重点有助于实现实时pTx脉冲设计方法。这将允许将实时更新应用于扫描仪，补偿在整个扫描过程中发生的患者运动，因此更准确和有效地消除所有运动引起的影响。我正在使用机器学习方法来训练神经网络，模拟训练数据用于开发方法，然后进行实验测试。我的工作影响广泛。通过消除对pTx的运动相关担忧，UHF MRI的优势（例如更高的图像分辨率）可以应用于临床。癫痫和MS诊断和预后等领域已经在研究背景下证明了这一点的好处，但这里提到的技术挑战目前阻碍了其广泛或临床应用