Short Axis EPI for Diffusion Tensor MRI at High Field

描述(申请人提供)：动机-扩散张量成像(DTI)是一种MRI方法，用于无创定量绘制各向异性水扩散图，从而可以研究白质(WM)的微观结构。DTI在帮助了解白质和成熟延迟的病理生理学方面具有巨大的潜力。此外，它还可以对肿瘤患者的WM途径进行非侵入性追踪，并有助于诊断患有非局灶性疾病的患者。然而，DTI仍然受到技术缺陷的困扰，随着磁场的增加，这些缺陷变得更加棘手。这是不幸的，因为增加的磁场强度提供了更多的SNR，这是缺乏SNR的方法(如DTI)迫切需要的。由于他们的大小和其他特殊要求，尤其是儿科患者将成为DTI高场成像的主要受益者--特别是当结合更强大的功能磁共振成像和在这些更高视野下可以实现的结构成像时。在较高场下使用DTI的障碍包括：视野要求、缺乏合作、运动增加、非共振伪影增加、显著的射频不均匀性以及射频能量沉积增加。目标-拟议项目的主要目标是通过新的采集/重建技术显著改善高场(即3T和7T)的DTI，这些技术可以减少失真，提高对运动的免疫力，减少射频沉积和翻转角度变化，并提供更好的空间分辨率，从而实现改进的儿科和成人高场DTI。具体目标是开发和优化扩散张量短轴读出EPI(sr-EPI)(A.1)的采集和重建方法，并通过将优化的sr-EPI DTI采样策略与并行传输相结合来调查和帮助重新点燃人们对7T DTI的兴趣，以及通过增加多回声读出器来进一步提高扫描效率(a.2)。这些目标预测了向更高场强的转变，旨在为临床环境(3T)提供强大的成像协议，同时提供克服当前超高场强方法中的缺点的手段。方法-在A.1中，将开发用于非共振、涡流和运动校正的新方案。此外，还将开发一种高效的并行成像重建算法，以补充一系列建议的SNR、SAR和扫描时间高效的SR-EPI技术。在A.2中，与经验丰富的合作者团队合作将允许在我们的7T上实施并行传输技术。结合“精确的”失真模型，这些B1/B0校正方法完美地补充了SR-EPI的快速变体。通过增加RF重新聚焦的多刀片/盲读取器，扫描效率将进一步提高。所有提出的捕获和重建技术都将在模拟和模型研究中进行优化。在这五年期间，总共将有200名受试者(儿童和成人)参加广泛的测试。最佳图像质量将由量化指标和人类观察者决定。 意义-我们相信，成功实现这些目标有望显著改善DTI，覆盖范围超出高场和儿科患者，从而提高DTI的整体效用。白质和神经束投影的异常可以为几种攻击白质的疾病的病理生理学提供重要的见解，并进一步了解患有和不患有白质障碍的儿童的特定神经发育轨迹。我们研究的成功将是非常有价值的，因为它将在高领域为进一步的临床重点研究和基础神经科学研究建立基本的方法学框架。

DESCRIPTION (provided by applicant): MOTIVATION - Diffusion Tensor Imaging (DTI) is an MRI method for noninvasive quantitative mapping of anisotropic water diffusion, thereby allowing the investigation of white matter (WM) microstructure. DTI holds tremendous potential for aiding the understanding of pathophysiologies of white matter and delayed maturation. In addition, it enables non-invasive tracing of WM pathways in tumor patients and is also helpful for diagnosing patients harboring non-focal disease. However, DTI still suffers from technical shortcomings which become even more problematic with increasing magnetic fields. This is unfortunate since increased magnetic field strengths offer substantially more SNR that is desperately needed for an SNR-starved method such as DTI. Because of their size and other specific requirements, especially pediatric patients would be major benefactors from DTI high field imaging - particularly when combined with more powerful fMRI and structural imaging achievable at these higher fields. Obstacles to using DTI at higher fields include: FOV requirements, lack of cooperation, increased motion, increase off-resonance artifacts, significant RF inhomogeneity, and increased RF energy deposition. AIMS - The main objective of the proposed project is to create significant improvements in DTI at high field (i.e. 3T and 7T) via novel acquisition/reconstruction techniques that reduce distortions, improve immunity to motion, diminish RF deposition and flip angle variation, and provide better spatial resolution so that improved pediatric and adult high-field DTI is enabled. The specific aims are to develop and optimize acquisition and reconstruction methods for diffusion tensor short-axis-readout EPI (sr-EPI) (A.1), and investigate and help to rekindle interest in 7T DTI by incorporating optimized sr-EPI DTI sampling strategies with parallel transmit as well as to further boost scan efficiency by adding multi-echo readouts (A.2). Anticipating the move toward higher-field strengths, these aims are designed to provide a robust imaging protocol for the clinical environment (3T), while providing the means to overcome short-comings in current ultra-high field strength methodologies. METHODS - In A.1, novel schemes for off-resonance, eddy-current, and motion correction will be developed. In addition, an efficient parallel imaging reconstruction algorithm will be developed to compliment a family of proposed SNR-, SAR-, and scan time-efficient sr-EPI techniques. In A.2, work with an experienced group of collaborators will allow the implementation of parallel transmit technology on our 7T. Together with an 'exact' distortion model, these B1/B0 correction methodologies ideally compliment a fast variant of sr-EPI. By adding RF-refocused multi-blade/blind readout the scan efficiency will be increased even further. All proposed acquisition and reconstruction techniques will be optimized both in simulations and phantom studies. A total number of subjects of 200 (children and adults) will be enrolled over this five year period for extensive testing. Optimal image quality will be determined by quantitative metrics and human observers. SIGNIFICANCE -We believe successful attainment of these aims promises to significant improvements in DTI, reaching beyond high field and pediatric patients, and hence greater overall utility of DTI. Abnormalities in WM and tract projections could provide crucial insights in the pathophysiology of several diseases that attack white matter, and further the understanding of specific neurodevelopmental trajectories of children with and without WM disorders. The success of our research effort would be of great value since it would build the basic methodological framework at high field for further clinically focused studies and basic neuroscience research.