Instrumentation and Methods for Magnetic Resonance Imaging

这项研究计划将改善磁共振成像（MRI）技术，不仅提高成像性能（例如，信噪比（SNR）、分辨率、速度）以及安全性和患者体验。这些目标在很大程度上取决于射频（RF）信号检测器或“线圈”，其放置在患者周围并用于信号激发和信号接收。 本研究计划的第一个核心目标是通过利用MRI磁场强度（以特斯拉或T测量）高于临床使用的磁场强度（1.5和3.0 T）的更好成像性能来改善躯干和腹部的MRI。虽然低于一些研究中心的7 T，但阿尔伯塔大学的4.7 T提供了在我们认为是“甜蜜点”的中等场强下进行身体成像（以前从未做过）的独特机会。由于短的RF波长，较高的场导致图像中的斑片状亮区和暗区。尽管在明亮区域中可实现高SNR，但由于黑暗区域可能隐藏放射科医师不可见的疾病，因此斑块损害图像质量并妨碍临床使用。在7 T时，斑块非常突出，如果没有最先进的方法，就不可能在足够大的视场内消除，这在技术上具有挑战性，需要专家监督才能可靠地工作。事实上，美国FDA已经批准7 T仅用于头部和四肢的临床使用。我们将在4.7 T下构建身体成像所需的线圈，并将图像质量与3 T和7 T下的图像质量进行比较。 该研究计划的第二个核心目标是开发创新和先进的仪器，首先是用于比吸收率（SAR）校准的可靠探测器。信号激励使用RF脉冲，其不可避免地加热患者的身体。因此，MRI扫描仪需要实时SAR监测，以确保加热不会造成伤害。发射电离辐射的器械（例如，X光机）使用标准化程序进行校准，但SAR监测系统由每个制造商使用专有方法进行校准。我们将开发一个强大的“SAR检测器”和方法来校准SAR监视器，以允许不同扫描仪的SAR水平的标准化比较。我们还将开发技术，使真正符合人体工程学的“可穿戴”线圈，而不是目前使用的笨重，令人生畏的笼子。实现这一点所需的一个组件是更好的RF开关，以使灵敏的仅接收线圈免受发射脉冲的影响。目前使用的两种类型的开关都存在发热或可靠性低等问题，并且它们都需要控制线，这使得布线复杂化。我们将实现没有这些限制的转变。最后，我们将使我们为直线加速器-MR放射治疗机设计的轻型线圈适应PET-MR扫描仪，PET-MR扫描仪也需要对X射线基本透明的线圈。

This research program will improve magnetic resonance imaging (MRI) technology and enhance not only the imaging performance (e.g., signal-to-noise ratio (SNR), resolution, speed) but also safety and patient experience. These goals depend greatly on the radio frequency (RF) signal detectors or "coils", which are placed around the patient and used for signal excitation and for signal reception. The first core goal of this research program is to improve MRI in the torso and abdomen by taking advantage of better imaging performance that is possible with MRI magnetic field strengths (measured in tesla or T) that are higher than those used clinically (1.5 and 3.0 T). While lower than the 7 T available at some research centres, the 4.7 T at the University of Alberta offers the unique opportunity to do body imaging (never done before) at this intermediate field strength which we believe is the “sweet spot”. Higher fields cause patchy bright and dark regions in the images because of the short RF wavelength. Despite the high SNR achievable in the bright regions, the patchiness compromises image quality and precludes clinical use because the dark regions could conceal disease invisible to a radiologist. At 7 T, patchiness is very prominent and impossible to eliminate over a large enough field of view without the most advanced methods, which are technically challenging and require expert supervision to work reliably. Indeed, the US FDA has cleared 7 T for clinical use only on the head and limbs. We will build the coils needed for body imaging at 4.7 T and compare image quality with that at 3 and 7 T. The second core goal of this research program is to develop enabling innovations and advanced instrumentation, beginning with a reliable detector for specific absorption rate (SAR) calibration. Signal excitation uses RF pulses which inevitably heat the patient's body. Therefore MRI scanners need real-time SAR monitoring to ensure the heating does not cause injury. Devices that emit ionizing radiation (e.g., x-ray machines) are calibrated using standardized procedures, but the SAR monitoring system is calibrated by each manufacturer using proprietary methods. We will develop a robust “SAR detector” and method to calibrate the SAR monitor, to allow a standardized comparison of SAR levels from different scanners. We will also develop technology to enable truly ergonomic “wearable” coils, instead of the bulky, intimidating cages currently in use. One component needed to achieve this is a better RF switch to make sensitive receive-only coils immune to the transmit pulses. The two types of switch in current use have problems such as generating heat or low reliability, and they both require control wires that complicate the cabling. We will realise a switch without these limitations. Finally, we will adapt the lightweight coils we designed for linac-MR radiation therapy machines to PET-MR scanners which also require coils that are essentially transparent to x-rays.