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

功能性磁共振成像（fMRI）可以前所未有地深入了解我们的大脑功能。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。超声平面成像（echo-planar imaging， EPI）是目前广泛应用于BOLD功能磁共振成像（fMRI）的一种方法，该方法在良好的时空分辨率下具有良好的灵敏度。严重的缺点是，EPI不仅对神经元激活过程中期望的微观磁场变化敏感，而且对不同磁化率区域附近的不期望的宏观磁场变化敏感，特别是空气腔。这些易感性伪影导致信号丢失，有效地阻止了许多与现代神经科学高度相关的大脑区域的激活检测。因此，无伪影技术的发展仍然是许多神经科学和临床应用功能磁共振成像的关键要求。例如，它将促进对仍然知之甚少的记忆网络的研究，并有助于理解像阿尔茨海默病或情绪和压力障碍这样的疾病。我提出了一套高度创新的发展方案，通过定制射频脉冲和并行传输（pTX）技术来补偿EPI信号损失伪像。具体来说，目标是开发一种同时用于3和7特斯拉的3D垫片，该垫片具有生成几乎无伪影图像的潜力。这结合了在八通道pTX系统上设计1D和2D光谱空间脉冲，并结合了最近开发的同步z-shim技术。我们将通过模拟、模拟实验和应用于志愿者的临床功能磁共振成像研究来评估这一努力。如果成功，这些方法将对fMRI在神经科学和临床应用中的能力产生相当大的影响，并将对定制射频脉冲设计领域做出重大的创新贡献。

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.