RF Encoding for Gradient-Free MRI

用于无梯度 MRI 的射频编码

• 批准号: 8828416
• 负责人: William A Grissom
• 金额: $ 19万
• 依托单位: VANDERBILT UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-25 至 2016-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8828416
• 关键词: Accounting; Address; Algorithm Design; Algorithms; Amplifiers; Base Sequence; Clinical; Data; Dependence; Development; Dimensions; Frequencies; Generations; Goals; Heating; Human; Image; Left; Limb structure; Location; Magnetic Resonance Imaging; Magnetism; Maps; Methods; Noise; Patients; Performance; Peripheral Nerve Stimulation; Phase; Physiologic pulse; Process; Protocols documentation; Protons; Relaxation; Research; Rotation; Signal Transduction; Slice; Sodium; Solutions; Staging; Surface; System; Techniques; Technology; Three-Dimensional Imaging; Time; Tissues; Translating; Translations; base; compliance behavior; cost; design; image reconstruction; imaging modality; improved; innovation; magnetic field; meetings; novel; public health relevance; radiofrequency; reconstruction; success; transmission process

DESCRIPTION (provided by applicant): The goal of this project is to develop new radiofrequency (RF) gradient encoding methods to spatially encode signals in MRI. The methods would enable silent, low-cost 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 expensive, representing around 20-25% of the cost of a clinical scanner. 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 en- joyed by B0 gradients, or a straightforward path to convert existing B0 gradient-based MRI acquisition techniques to use RF encoding. The methods proposed in this project will be the first to meet these requirements, and will thus represent the first truly viable RF gradient-based imaging methods. The central innovation of this project is to use the Bloch-Siegert 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 new RF gradient coils and other RF hardware to enable 2D and 3D Cartesian imaging at 0.5 Tesla, including hardware strategies for simultaneous RF transmission and reception to enable frequency encoding by Bloch-Siegert shift. The second Aim is to develop new RF-encoded pulse sequences based on the Bloch-Siegert shift, leveraging recent innovations in RF pulse design for Bloch-Siegert phase encoding, and in RF pulse design for RF gradient-based slice-selective excitation. The third Aim is to develop robust algorithms to reconstruct images from RF-encoded data. Successful completion of these Aims would broadly prove the feasibility of the proposed RF encoding methods for MR imaging, paving the way for translation to humans.

描述（由申请人提供）：该项目的目的是开发新的射频（RF）梯度编码方法，以在MRI中进行空间编码信号。这些方法将使无声，低成本的MRI系统能够大大降低成像成本，并改善患者的合规性和舒适性。 在常规MRI中，接收的信号基于其时间频率定位到其原始频率的空间位置，该时间频率使用与扫描仪的主（B0）磁场平行的磁场进行控制，并在空间跨空间进行线性变化。这些B0梯度领域有很多问题：它们响亮，引起周围神经刺激，损害患者的舒适感；由于线圈的高电感，它们的切换时间相对较长。他们需要笨重的冷却系统和定制的放大器；它们很昂贵，约占临床扫描仪成本的20-25％。解决这些问题的一种潜在解决方案是用RF梯度代替B0梯度，而RF梯度是无声且低成本的。不幸的是，尽管其潜在的RF梯度编码尚未成为临床或商业上的成功。这很大程度上是由于以下事实：现有的RF梯度编码方法提供了造影剂的开发与空间编码之间的正交性，而空间编码是由B0梯度所吸引的，或者是转换现有的基于B0梯度的MRI释放技术来使用RF编码的直接途径。该项目中提出的方法将是第一个满足这些要求的方法，因此将代表第一个真正可行的基于RF梯度的成像方法。 该项目的中心创新是使用Bloch-Siegert Shift进行空间编码MRI信号。与B0梯度一样，这种编码机制是基于直接在横向平面中的相位移位到磁化的应用，因此不会调节横向磁化的大小，而图像对比度不受空间编码的影响。该项目的第一个目的是开发新的RF梯度线圈和其他RF硬件，以在0.5 Tesla处启用2D和3D笛卡尔成像，包括用于同时进行RF传输和接收的硬件策略，以通过Bloch-Siegert Shift启用频率编码。第二个目的是根据Bloch-Siegert Shift开发新的RF编码的脉冲序列，利用Bloch-Siegert相编码的RF脉冲设计中的最新创新，以及用于基于RF梯度的SLICE SLICE-SELCEECTION启动激发的RF脉冲设计。第三个目的是开发可靠的算法来从RF编码的数据中重建图像。这些目标的成功完成将广泛地证明提出的RF编码方法的可行性，为将其转换为人类铺平了道路。