Discovery and Applied Research for Technological Innovations to ImproveHuman Health

项目摘要 该项目的目标是将R21项目中开发的RF编码方法转化为人体成像， 在非常低场的人体MRI扫描仪上实现它们。它的成功完成将使无声，低成本 和更便携的MRI系统，导致成像成本的大幅降低和患者的改善。 顺从和舒适。 在常规MRI中，基于接收信号的时间位置，将接收信号定位到其起源的空间位置。 频率，其使用平行于扫描仪的主（B 0）场的磁场来控制， 在空间中线性变化。这些B 0梯度场存在许多问题：它们很吵， 周围神经刺激，损害患者舒适度;由于 高电感线圈;他们需要庞大的冷却系统和定制放大器;他们是昂贵的， 它占临床扫描仪成本的25-30%。B 0梯度编码还遭受空间误差 由于伴随项，其随着B 0场强度的降低而增加，并将限制 新兴的便携式和低成本MRI系统。这些问题的潜在解决方案是替换B 0梯度 具有射频梯度，这是无声的和低成本的。不幸的是，尽管其潜在的RF梯度编码 尚未取得临床或商业成功。这在很大程度上是由于没有现有的RF梯度 编码方法提供了对比度显影和空间编码之间的正交性， B 0梯度，或将现有基于B 0梯度的MRI扫描转换为使用RF编码的直接路径。的 本项目中开发的方法是第一个满足这些要求的方法，因此也是第一个真正可行的方法 基于RF梯度的成像方法。 该项目的核心创新是使用Bloch-Siegert（BS）移位对MRI进行空间编码 信号了与B 0梯度一样，该编码机制基于将相移应用于磁化 直接在横向平面中，因此不调制横向磁化的大小， 使得图像对比度不受空间编码的影响。本项目的第一个目标是开发阵列和螺线管 RF梯度线圈和相关RF硬件，用于在人体上实现2D和3D笛卡尔脑成像0.0475 Tesla MRI扫描仪，包括同步射频发射和接收策略，以实现频率 通过BS移位进行编码。第二个目标是开发和实现用于脑的射频编码脉冲序列 基于BS偏移的成像，利用该项目R21阶段的关键发展，包括扫频射频 用于相位编码的脉冲、用于BS频率编码的理论基础和脉冲序列，以及用于 基于RF梯度的切片选择性激励和切片编码。第三个目标是发展图像重建 并对人脑成像中的编码方法进行了评价。这些目标的成功实现将建立 第一个可行的完全射频编码人体成像系统，为商业化和临床应用铺平了道路。

Project Summary The goal of this project is to translate RF encoding methods developed in an R21 project to human imaging, by implementing them on a very low field human MRI scanner. Its successful completion will enable silent, low-cost and more portable MRI systems, leading to a substantial reduction in the cost of imaging and improved patient compliance and comfort. In conventional MRI, a received signal is localized to its spatial location of origin based on its temporal frequency, which is controlled using magnetic fields that are parallel to the main (B0) field of the scanner and vary linearly across space. There are many problems with these B0 gradient fields: they are loud and induce peripheral nerve stimulation, compromising patient comfort; they have relatively long switching times due to the high inductance of the coils; they require bulky cooling systems and customized amplifiers; and they are expen- sive, representing 25-30% of the cost of a clinical scanner. B0 gradient encoding also suffers from spatial errors due to concomitant terms, which increase with decreasing B0 field strength and will limit the performance of emerging portable and low-cost MRI systems. A potential solution to these problems is to replace B0 gradients with RF gradients, which are silent and low-cost. Unfortunately, in spite of its potential RF gradient encoding has not yet become a clinical or commercial success. This is largely due to the fact that no existing RF gradient encoding method offers the orthogonality between contrast development and spatial encoding that is enjoyed by B0 gradients, or a straightforward path to convert existing B0 gradient-based MRI scans to use RF encoding. The methods developed in this project are the first to meet these requirements, and will thus be the first truly viable RF gradient-based imaging methods. The central innovation of this project is to use the Bloch-Siegert (BS) shift to spatially encode the MRI signal. As with B0 gradients, this encoding mechanism is based on the application of phase shifts to magnetization directly in the transverse plane, and therefore does not modulate the magnitude of the transverse magnetization, leaving image contrast unaffected by spatial encoding. The first Aim of the project is to develop array and solenoid RF gradient coils and associated RF hardware to enable 2D and 3D Cartesian brain imaging on a human 0.0475 Tesla MRI scanner, including strategies for simultaneous RF transmission and reception to enable frequency encoding by BS shift. The second Aim is to develop and implement RF-encoded pulse sequences for brain imaging based on the BS shift, leveraging key developments from the R21 phase of the project including swept RF pulses for phase encoding, a theoretical basis and pulse sequence for BS frequency encoding, and RF pulses for RF gradient-based slice-selective excitation and slice-encoding. The third Aim is to develop image reconstructions and evaluate the encoding methods in human brain imaging. Successful completion of these Aims will establish the first viable fully RF-encoded human imaging system and pave the way for commercialization and clinical use.