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编码方法转换为人类成像，通过 在一台非常低fi的人体核磁共振扫描仪上实现它们。它的成功完成将使无声、低成本 和更便携的核磁共振系统，大大降低了成像成本，改善了患者状况 合规性和舒适度。 在传统的磁共振成像中，接收到的信号基于其时间定位到其起源的空间位置 频率，使用与扫描仪的主(B0)fi场平行的磁fi场来控制 在空间中呈线性变化。这些B0渐变fi场有很多问题：它们很吵，而且很诱人 周围神经刺激，影响患者舒适性；由于 线圈的高电感；它们需要庞大的冷却系统和定制的放大器fi；而且它们非常昂贵- Ssive，占临床扫描仪成本的25%-30%。B0梯度编码也会受到空间误差的影响 由于伴随项随着B0fi焊接强度的降低而增加，并将限制 新兴的便携式和低成本核磁共振系统。这些问题的一个潜在解决方案是替换B0梯度 使用射频梯度，这是静音和低成本。不幸的是，尽管其潜在的RF梯度编码 尚未在临床或商业上取得成功。这很大程度上是因为没有现有的射频梯度 编码方法提供对比度显影和空间编码之间的正交性，这是 B0梯度，或将现有的基于B0梯度的MRI扫描转换为使用RF编码的直接路径。这个 在这个项目中开发的方法是第一个满足这些需求的fi，因此将是第一个真正可行的fi 基于射频梯度的成像方法。 该项目的中心创新是使用Bloch-Siegert(BS)移位对MRI进行空间编码 信号。与B0梯度一样，这种编码机制基于相移对磁化的应用 直接在横向平面中，因此不调制横向磁化的大小， 使图像对比度不受空间编码的影响。该项目的首要目标是开发阵列和螺线管 射频梯度线圈和相关的射频硬件，以实现在人类0.0475上进行2D和3D笛卡尔脑成像 特斯拉核磁共振扫描仪，包括同时发送和接收射频以启用频率的策略 通过BS移位进行编码。第二个目标是开发和实现用于大脑的射频编码脉冲序列 基于BS转换的成像，利用项目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 基于射频梯度的片层选择激励和片层编码。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确立 fi是第一个可行的完全射频编码的人体成像系统，并为商业化和临床使用铺平了道路。

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.