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。所取得的进展包括为国际空间站（ISS）和加拿大航天局（CSA）设计手腕大小的MRI，以及建造和测试两个手腕大小的无梯度MRI。 无梯度MRI的核心是一种新型射频（RF）发射线圈。线圈的射频场设计允许直接空间编码，无需磁场梯度-无梯度MRI。当与低场（500高斯）结合时，产生非常便携的MRI。到目前为止，两个腕部MRI的磁体质量均小于5 kg。RF幅度和RF相位两者的空间变化可以用于图像编码。我现有的一个手腕MRI结合了不同的RF场与RF线圈的电动运动。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。这两种MRI设计将与其他设计一起沿着进一步开发。 这项研究将由HQP学员按照非常成功的方法进行，迄今为止，使用手腕大小的MRI进行基于数学的研究项目和调查。预计将修改现有的MRI和建造一个手腕大小的MRI。一家初创公司计划建造头盔大小的无梯度MRI，用于加拿大北部现有的远程存在诊所。但我们对NSERC赞助的研究的重点将是手腕大小的MRI，因为我们的目的是发展MRI工程，而不是研究解剖学或生理学。这种方法还可以降低硬件成本。 ISS-MRI设计使用高度均匀的磁场和线性变化的发射RF相位分布。所提出的工作使用非线性变化的发射RF相位分布。非线性变化的相位分布意味着傅立叶变换不能直接用于从接收到的RF信号重建图像，除了在RF发射线圈的中心附近的非常小的视场中。还需要使用复合脉冲的新型自旋回波脉冲序列。我们的手腕大小的MRI也不使用均匀磁场，因此对象中的等磁表面被激发以给出非平面切片。这些新方法需要超越标准傅立叶变换的数学变换来进行图像重建。数学重建算法将是一些研究项目的重点。其他研究项目将涉及射频线圈设计，射频脉冲序列设计和磁场设计。LT Imaging和MRI Tech将提供项目所需的MRI硬件。 便携式无梯度MRI有可能取代X射线和超声作为医学成像模式。拟议的研究将使MRI技术朝着这些未来的角色发展，以提供可访问的医疗诊断。

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.