Gradient-Free Quantitative MRI using a Combination of B1-Selective Excitation and Fingerprinting

项目摘要 磁共振成像（MRI）是最重要的医学成像模式之一，因为其具有良好的成像质量。 检测和表征全身病变的能力。然而，MRI的使用受到其 昂贵的硬件，复杂的选址要求和典型的定性图像，这需要高度熟练的 放射科医生来解释。该项目提出了一种全新的MRI编码方法， 更便宜和更灵活的定量MRI扫描仪。 目前，绝大多数MRI扫描使用两种主要方法进行编码：B 0梯度 以及使用接收器线圈阵列的并行成像。B 0梯度占孔直径的很大一部分， 声音大并引起外周神经刺激，损害患者舒适度;它们具有相对长的 开关时间由于线圈的高电感;它们需要庞大的冷却系统和定制的AM， 它们是昂贵的，占临床扫描仪成本的25-30%;并且它们必须小心地 专为扫描仪的B 0磁铁而设计和定制。B 0梯度编码还遭受空间误差， 伴随的条款，随着B 0场强度的下降而增加，并将限制新兴市场的表现。 便携式低成本MRI系统。并行成像通过区分信号来实现扫描加速 大的空间距离，但不能自己编码完整的图像。虽然有些人提出了第三类 在使用射频发射（B1+）梯度的编码方法中，迄今为止所描述的方法都不 由于其性能的实际限制，严格的硬件要求， 以及在图像对比度方面缺乏可伸缩性。 该项目将开发和验证第四种，基于并行计算的全新MRI编码方法。 使用由具有在线放大器的无线RF线圈单元产生的B1+选择性脉冲进行传输， RF发射和接收，结合受MR Finger启发的采集和重建过程， 打印（MRF）。这种新方法，通过章动和指纹选择性编码（SENF），完全 消除了对B 0梯度的需要，并与各种磁体设计和可伸缩交流电源兼容， 收购战略。与以前的B1+成像方法不同，SENF没有严格的空间变化要求 在射频梯度场，这使得灵活的系统设计，相同的线圈可用于空间增强， 编码和信号接收。此外，代替遭受由于复杂的自旋动力学而引起的误差， RF编码，SENF利用这些动态特性来区分定量组织参数。 该项目的成功完成将使新一代更便宜，更方便，更模块化， 和低维护的MRI扫描仪，其定量输出可以更直接地与疾病相关， 组织状态。

Project Summary Magnetic Resonance Imaging (MRI) is one of the most important medical imaging modalities because of its ability to detect and characterize lesions throughout the body. However, access to MRI is severely limited by its expensive hardware, complex siting requirements and typically-qualitative images, which require highly skilled radiologists to interpret. This project proposes a fundamentally new way to encode MRI that could enable sub- stantially cheaper and more flexible quantitative MRI scanners. Today the overwhelming majority of MRI scans are encoded using two primary methods: B0 gradients and parallel imaging using an array of receiver coils. B0 gradients take up a significant fraction of the bore diam- eter; 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 am- plifiers; they are expensive, representing 25-30% of the cost of a clinical scanner; and they must be carefully designed and customized to a scanner's B0 magnet. 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. Parallel imaging enables scan acceleration by differentiating signals across large spatial distances, but cannot encode complete images on its own. While some have proposed a third class of encoding methods using radiofrequency transmit (B1+) gradients, none of the methods described to date have been translated into clinical use because of practical limits on their performance, stringent hardware requirements and lack of flexibility in image contrast. This project will develop and validate a fourth, fundamentally new way to encode MRI based on parallel transmission using B1+-selective pulses produced by wireless RF coil units with on-coil amplifiers that perform RF transmission and reception, combined with an acquisition and reconstruction process inspired by MR Finger- printing (MRF). This new method, Selective Encoding through Nutation and Fingerprinting (SENF), completely eliminates the need for B0 gradients and is compatible with a wide range of magnet designs and flexible ac- quisition strategies. Unlike previous B1+ imaging methods, SENF places no strict spatial variation requirements on the RF gradient fields, which enables flexible system design, and the same coils can be used for spatial en- coding and signal reception. Furthermore, instead of suffering from errors due to complex spin dynamics during RF encoding, SENF leverages those dynamics to its advantage to differentiate quantitative tissue parameters. Successful completion of this project will enable a new generation of cheaper, more accessible, more modular, and lower-maintenance MRI scanners with quantitative outputs that can be more directly related to disease and tissue states.