Novel RF-pulses and parallel-transmit methods for compensation of signal loss in functional MRI at 3 and 7 Tesla

功能磁共振成像(FMRI)可以前所未有地深入了解我们大脑的功能。通过检测伴随神经元活动的局部血氧水平依赖(BOLD)信号变化，非侵入性地识别激活区域。回声平面成像(EPI)是BOLD功能磁共振成像中广泛使用的方法，它具有良好的时空分辨率，具有良好的灵敏度。EPI的严重缺点是不仅对神经元激活过程中所需的微观磁场变化敏感，而且对不同磁化率区域附近的宏观磁场变化也很敏感，特别是在气腔附近。这些敏感性伪影会导致信号丢失，从而有效地阻止在现代神经科学中高度相关的许多大脑区域进行激活检测。因此，无伪影技术的发展仍然是许多神经科学和fMRI临床应用的关键要求。例如，它将促进对仍然知之甚少的记忆网络的研究，并有助于了解阿尔茨海默病或情绪和压力障碍等疾病。我提出了一系列高度创新的开发，通过定制的射频脉冲和并行传输(PTX)技术来补偿EPI信号损失伪影。具体地说，目标是开发一种同时使用3特斯拉和7特斯拉的3D垫片，有可能生成几乎没有伪影的图像。这包括在八通道PTX系统上设计一维和二维光谱-空间脉冲，并结合最近开发的同步Z-填补技术。这一努力将通过模拟、体模实验和在志愿者临床功能磁共振研究中的应用来评估。如果成功，这些方法将对fMRI在神经科学和临床应用方面的能力产生相当大的影响，并将对定制RF脉冲设计领域做出重大的创新性贡献。

Functional magnetic resonance imaging (fMRI) allows unprecedented insights into the functioning of our brain. Activated regions are identified non-invasively by detecting local blood oxygenation-level dependent (BOLD) signal changes that accompany neuronal activity. The widely used method for BOLD fMRI is echo-planar imaging (EPI) which offers favorable sensitivity at good spatio-temporal resolution. The serious drawback is that EPI is not only sensitive to the desired microscopic magnetic changes during neuronal activation, but also undesired macroscopic magnetic field variations near regions of differing magnetic susceptibility, especially the air cavities. These susceptibility artifacts result in signal loss that effectively prohibits activation detection in many brain areas that are highly relevant in modern neuroscience. Development of artifact free techniques therefore remains a crucial requirement for many neuroscientific and clinical applications of fMRI. It would for instance facilitate studies of the still poorly understood memory network, and help understand ailments like Alzheimer disease or mood and stress disorders.I propose a set of highly innovative developments to compensate the EPI signal loss artifact by means of tailored RF pulses and parallel transmit (pTX) techniques.Specifically, the aim is to develop a simultaneous 3D shim for use at 3 and 7 Tesla that has the potential of generating virtually artifact free images. This incorporates the design of 1D and 2D spectral-spatial pulses on an eight-channel pTX system, combined with the recently developed simultaneous z-shim technique.The endeavor will be assessed by simulations, phantom experiments and application to clinical fMRI studies on volunteers. If successful the methods will have considerable impact on the abilities of fMRI in its neuroscientific and clinical applications, and will constitute a significant and innovative contribution to field of tailored RF pulse design.