Spectral Spatial RF Pulses for Gradient Echo fMRI

描述（由申请人提供）：本提案“用于梯度回波MRI的频谱-空间射频脉冲”是一项MRI技术开发项目，旨在设计使用3 T下的单个和多个发射器的频谱-空间射频（RF）激励。设计这些脉冲的目的是抑制不需要的脂质信号，减少磁化率伪影，并改善梯度回波MRI中的切片轮廓（B1+）均匀性。梯度回波应用，如血氧水平依赖（BOLD）脑功能MRI（fMRI）的困扰，由于磁化率的变化在大脑下部区域的大信号空隙。此外，良好的梯度回波对比度所需的高场使图像易于因B1+不均匀性而发生强度变化。解决这些局限性的方法对于充分利用MRI的优势来改善医疗保健和研究非常重要。我们首先提出了一个或多个发射机上的切片和频率选择性的2D频谱空间脉冲。这些脉冲可用于脂质抑制和消除通过平面的磁化率梯度。磁化率伪影校正假设跨平面梯度是非共振频率的函数。获取场图以确定通过平面梯度和非共振的空间分布将测试该假设。然后将利用并行传输方法来利用地图的空间变化。下一种方法将是为并行发射器设计4D频谱-空间脉冲，以开发同时校正跨平面磁化率伪影、平面内发射器（B1+）不均匀性并提供脂质抑制的激励。然后，脉冲生成算法将被移植到图形编程单元（GPU）上使用，以提高速度。将通过模拟、体模和人体对照梯度回波成像研究对脉冲进行测试和表征。脉冲的最终验证将使用人类对照扫描与磁敏感加权成像（SWI），T2* 映射，屏气BOLD功能磁共振成像实验。成功开发本提案中描述的方法将克服梯度回波MRI的主要局限性，使以前不可能的广泛临床应用成为可能。此外，频谱空间脉冲和并行发射机的应用对于该提议是新颖的，并且代表了多维RF脉冲设计的一大步。 公共卫生相关性：磁共振成像（MRI）是一种强大的非侵入性技术，用于观察人体的解剖结构，结构和功能。特别地，梯度回波MRI可用于包括脑功能和结构成像的许多应用。然而，足够的梯度回波对比度所需的高场也会产生图像伪影形式的挑战和障碍。本项目的目标是开发和确认一个技术系统，以纠正这些场相关的MRI伪影。拟议的研究将最终有助于降低MRI检查的成本和持续时间，并提高诊断准确性。

DESCRIPTION (provided by applicant): This proposal "Spectral-Spatial RF Pulses for Gradient Echo MRI" is an MRI technology development project to design spectral-spatial Radio Frequency (RF) excitations using single and multiple transmitters at 3T. These pulses will be designed with the goal of suppressing unwanted lipid signal, reducing susceptibility artifacts, and improving slice profile (B1+) uniformity in gradient echo MRI. Gradient echo applications such as blood oxygen level dependent (BOLD) brain functional MRI (fMRI) are plagued by large signal voids in the inferior brain regions due to magnetic susceptibility variations. Furthermore, the high fields required for good gradient echo contrast make the images prone to intensity variations from B1+ inhomogeneity. Methods that address these limitations are important to exploit the full benefits of MRI for improved health care and research. We first propose 2D spectral spatial pulses for slice and frequency selectivity on one or multiple transmitters. These pulses can be used for both lipid suppression and the cancellation of the through-plane susceptibility gradient. The susceptibility artifact correction assumes that the through-plane gradient is a function of off- resonance frequency. Acquiring field maps to determine the spatial distribution of through-plane gradients and off-resonance will test this assumption. The spatial variations of the maps will then be exploited using parallel transmission methods. The next approach will be to design 4D spectral-spatial pulses for parallel transmitters to develop excitations that simultaneously correct for through-plane susceptibility artifact, in-plane transmitter (B1+) inhomogeneity, and provide lipid suppression. The pulse generation algorithms will then be ported for use on graphics programming units (GPUs) for increased speed. The pulses will be tested and characterized with simulations and phantom and human control gradient echo imaging studies. Final validation of the pulses will use human control scanning with susceptibility weighted imaging (SWI), T2* mapping, and breath-holding BOLD fMRI experiments. Success in developing the methods described in this proposal will overcome major limitations in gradient echo MRI, making feasible a broad range of clinical applications not previously possible. Furthermore, the application spectral-spatial pulses and parallel transmitters is novel to this proposal and represent a big step forward in multi-dimensional RF pulse design. PUBLIC HEALTH RELEVANCE: Magnetic resonance imaging (MRI) is a powerful and non-invasive technique for observing anatomy, structure, and function in the human body. In particular gradient echo MRI is useful for a number of applications including brain functional and structural imaging. However, the high fields required for adequate gradient echo contrast also produce challenges and obstacles in the form of image artifacts. The goal of this project is to develop and validate a system of techniques to correct for these field related MRI artifacts. The proposed research will ultimately aid in reducing the cost and duration of MRI examinations and provide improved diagnostic accuracy.