Instrumentation and Methods for Magnetic Resonance Imaging

这项研究计划将改进磁共振成像(MRI)技术，不仅提高成像性能(例如，信噪比(SNR)、分辨率、速度)，还将提高安全性和患者体验。这些目标在很大程度上取决于射频(RF)信号探测器或“线圈”，它们被放置在患者周围，用于信号激励和信号接收。该研究计划的第一个核心目标是通过利用更好的成像性能来改善躯干和腹部的MRI，而MRI磁场强度(以特斯拉或T为单位)高于临床使用的磁场强度(以1.5和3.0T为单位)。虽然低于一些研究中心提供的7T，但艾伯塔大学的4.7T提供了一个独特的机会，可以在这个中等磁场强度下进行身体成像(以前从未做过)，我们认为这是“甜蜜点”。由于射频波长较短，较高的场会在图像中产生斑片状的亮暗区域。尽管在明亮的区域可以实现高信噪比，但斑块会影响图像质量，并排除临床使用，因为暗区域可能隐藏放射科医生看不见的疾病。在7T，斑块非常突出，如果没有最先进的方法，在足够大的视野内是不可能消除的，这些方法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已经批准了7T仅用于头部和四肢的临床使用。我们将建造4.7 T的人体成像所需的线圈，并将图像质量与3 T和7 T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使能创新和先进的仪器，首先是用于特定吸收率(SAR)校准的可靠检测器。信号激励使用射频脉冲，这不可避免地会加热患者的身体。因此，核磁共振扫描仪需要实时监测SAR，以确保加热不会造成伤害。发射电离辐射的设备(例如X光机)使用标准化程序进行校准，但合成孔径雷达监测系统由每个制造商使用专有方法进行校准。我们将开发一种强大的“合成孔径雷达探测器”和方法来校准合成孔径雷达监视器，以便对不同扫描仪的合成孔径雷达水平进行标准化比较。我们还将开发技术，以实现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、可怕的笼子。实现这一点需要的一个组件是更好的射频开关，使敏感的仅接收线圈不受发射脉冲的影响。目前使用的两种类型的开关都存在发热或可靠性较低等问题，而且它们都需要控制线，从而使布线变得复杂。我们将实现一种没有这些限制的转换。最后，我们将把我们为直线加速器-MR放射治疗机设计的轻型线圈改造成PET-MR扫描仪，这也需要基本上对X射线透明的线圈。

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.