RADIOFREQUENCE (RF) PULSE DEVELOPMENT AND DESIGN FOR HIGH FIELD MRI

高场 MRI 射频 (RF) 脉冲开发和设计

基本信息

批准号：
7957223
负责人：
GERALD B MATSON
金额：
$ 1.1万
依托单位：
NORTHERN CALIFORNIA INSTITUTE/RES/EDU
依托单位国家：
美国
项目类别：
财政年份：
2009
资助国家：
美国
起止时间：
2009-07-01 至 2010-06-30
项目状态：
已结题

项目摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Overview: The promise of improved MRI results at high field strength is compromised by the difficulties encountered at high field, including: i) Non-uniform excitation, due to the non-uniform B1 field inherent at high field. Typically, the non-uniform excitation produces non-uniform tissue contrast, although other deleterious effects can be produced as well. ii) Large susceptibility gradients, which can distort slice positions unless large slice-select gradients are used. However, the limited RF power available on high field systems severely limits the gradient strength that can be used for T2-weighted images. The specific aims propose the further development and refinement of two new RF pulse designs to ameliorate these deleterious effects. In addition, further development of software for simulating MRI experiments is proposed to aid in effective implementation of these new RF pulses into suitably re-designed MRI experiments. Specific aim 1: Pulses with immunity to B1 inhomogeneity. The new B1-insensitive design is based on optimized concatenations of rectangular pulses applied along different axes in the rotating frame, where the optimization is for both uniform tip and immunity to resonance offset. The design focuses on excitation pulses, but includes extension of the method to spin echo and inversion pulses. Specific aim 2: Lowered peak voltage spin echo frequency-selective pulses. The new, lowered peak voltage design method consists of concatenation of conventional, frequency-selective pulses with gradients of alternating sign. The design includes spoiler gradients incorporated into the spin echo pulse to shorten the overall length of the pulse. Operation of these pulses in inhomogeneous B1 fields is also considered. Specific aim 3: Further development of MRI simulation software with inclusion of "inadvertent" magnetization transfer (MT) effects. The further development builds on software already developed for MP RAGE MRI experiments, and will include extended phase graph (EPG) algorithms to cover a wide range of MRI experiments. These simulations will aid in effective implementation of the new RF pulses, and avoid deleterious MT effects. A further use of these simulations is expected to be in the optimization of MRI sequences for 4.0 Tesla.

该子项目是利用该技术的众多研究子项目之一资源由 NIH/NCRR 资助的中心拨款提供。子项目及研究者 (PI) 可能已从 NIH 的另一个来源获得主要资金，因此可以在其他 CRISP 条目中表示。列出的机构是对于中心来说，它不一定是研究者的机构。概述：在高场强度下改善 MRI 结果的希望受到高场遇到的困难的影响，包括： i) 由于高场固有的不均匀 B1 场而导致不均匀激励。通常，不均匀的激励会产生不均匀的组织对比度，尽管也可能产生其他有害影响。 ii) 大的磁化率梯度，除非使用大的切片选择梯度，否则可能会扭曲切片位置。然而，高场系统上可用的有限射频功率严重限制了可用于 T2 加权图像的梯度强度。具体目标是进一步开发和完善两种新的射频脉冲设计，以改善这些有害影响。此外，建议进一步开发用于模拟 MRI 实验的软件，以帮助有效地将这些新的 RF 脉冲应用到适当重新设计的 MRI 实验中。具体目标 1：对 B1 不均匀性具有免疫力的豆类。新的 B1 不敏感设计基于旋转框架中沿不同轴施加的矩形脉冲的优化串联，其中优化是为了均匀尖端和抗共振偏移。该设计侧重于激励脉冲，但包括将方法扩展到自旋回波和反转脉冲。具体目标 2：降低自旋回波频率选择脉冲的峰值电压。新的降低峰值电压设计方法由传统的频率选择脉冲与交替符号梯度的串联组成。该设计包括将扰流梯度纳入自旋回波脉冲中，以缩短脉冲的总长度。还考虑了这些脉冲在不均匀 B1 场中的操作。具体目标 3：进一步开发 MRI 模拟软件，纳入“无意的”磁化转移 (MT) 效应。进一步的开发建立在已经为 MP RAGE MRI 实验开发的软件的基础上，并将包括扩展相图 (EPG) 算法以涵盖广泛的 MRI 实验。这些模拟将有助于有效实施新的射频脉冲，并避免有害的 MT 效应。这些模拟的进一步用途预计将用于优化 4.0 特斯拉的 MRI 序列。