Design and Testing Gradient Free Magnetic Resonance Imaging

在开发新一代无梯度磁共振成像仪方面取得的进展将继续下去。取得的进展包括为国际空间站(ISS)和加拿大航天局(CSA)设计了手腕大小的核磁共振成像，以及建造和测试了两个手腕大小的无梯度核磁共振成像。*无梯度核磁共振成像的核心是一种新型的射频发射线圈。线圈的射频场设计允许直接的空间编码，而不需要磁场梯度--无梯度磁共振成像。当结合低场(500高斯)，一个非常便携的核磁共振结果。到目前为止，两个手腕磁共振成像设备的磁体质量都不到5公斤。射频幅度和射频相位的空间变化均可用于图像编码。我现有的一个手腕磁共振成像结合了变化的射频磁场和电动化的射频线圈运动。我的另一个现有MRI使用空间变化的RF相位来实现空间编码。这两个磁共振成像设计将与其他设计一起进一步开发。*这项研究将由HQP受训人员进行，遵循迄今为止非常成功的方法，即进行基于数学的研究项目，并使用手腕大小的磁共振成像进行调查。预计将对现有的磁共振成像进行修改，并再建造一个手腕大小的磁共振成像。一家初创公司计划建造头盔大小的无梯度磁共振成像，用于加拿大北部现有的远程诊所。但我们对NSERC赞助的研究的重点将是手腕大小的磁共振成像，因为我们的目的是开发磁共振成像工程，而不是研究解剖学或生理学。这种方法还降低了硬件成本。*ISS-MRI设计使用了高度均匀的磁场和线性变化的传输射频相位分布。所提出的工作使用了非线性变化的发射射频相位分布。非线性变化的相位分布意味着傅里叶变换不能直接用于从接收的RF信号重建图像，除非在靠近RF发射线圈中心的非常小的视场中。还需要使用复合脉冲的新型自旋回波脉冲序列。我们手腕大小的核磁共振成像也不使用均匀的磁场，因此物体中的等磁面被激发以提供非平面切片。这些新方法需要超越标准傅里叶变换进行图像重建的数学变换。数学重建算法将是一些研究项目的重点。其他研究项目包括射频线圈设计、射频脉冲序列设计和磁场设计。LT成像和核磁共振技术公司将提供项目所需的核磁共振硬件。*便携式无梯度核磁共振有可能取代X射线和超声波作为医学成像手段。这项拟议的研究将推动核磁共振技术朝着提供可获得的医疗诊断的未来角色迈进。

The progress made in developing a new generation of gradient-free magnetic resonance imagers (MRIs) will continue. Progress made includes the design of a wrist-sized MRI for the International Space Station (ISS), for the Canadian Space Agency (CSA), and the construction and testing of two wrist-sized gradient-free MRIs.*** *At the heart of gradient-free MRI is a novel radio frequency (RF) transmitting coil. The RF field design of the coil allows for direct spatial encoding with no need for magnetic field gradients - gradient-free MRI. When combined with a low field (500 gauss), a very portable MRI results. The magnet mass of both wrist MRIs constructed to date is less than 5 kg. The spatial variation of both RF magnitude and RF phase can be used for image encoding. One of my existing wrist MRIs combines a varying RF field with motorized motion of the RF coils. My other existing MRI uses spatially varying RF phase to achieve spatial encoding. The two MRI designs will be developed further, along with other designs.*** *The research will be done by HQP trainees following the very successful approach, to date, of doing mathematically based research projects coupled with investigations using the wrist-size MRIs. Modification of the existing MRIs and construction of one more wrist-sized MRI is anticipated. A start-up company has been planned to build helmet-size gradient-free MRIs for use in existing remote-presence enabled clinics in the Canadian north. But our focus for the NSERC sponsored research will be wrist-sized MRIs because our purpose is to develop the MRI engineering and not to study anatomy or physiology. This approach also keeps the hardware costs down.*** *The ISS-MRI design uses a highly homogeneous magnetic field and a linearly varying transmitted RF phase profile. The proposed work uses non-linearly varying transmitted RF phase profiles. A non-linearly varying phase profile means that the Fourier transform cannot be used directly to reconstruct the image from the received RF signal, except in a very small field of view near the center of the RF transmit coil. Novel spin echo pulse sequences, using composite pulses, are also required. Our wrist-size MRIs also do not use homogeneous magnetic fields so that isomagnetic surfaces in the object are excited to give non-planar slices. These new approaches require mathematical transformations that go beyond the standard Fourier transformation for image reconstruction. Mathematical reconstruction algorithms will be the focus of some of the research projects. Other research projects will involve RF coil design, RF pulse sequence design and magnetic field design. LT Imaging and MRI Tech will provide the MRI hardware needed for the projects.*** *Portable gradient-free MRI has the potential to displace both x-ray and ultrasound as medical imaging modalities. The proposed research will move MRI technology toward those future roles to deliver accessible medical diagnostics.