Short Axis EPI for Diffusion Tensor MRI at High Field

描述（由申请人提供）：动机-扩散张量成像（DTI）是一种用于各向异性水扩散的无创定量标测的MRI方法，从而允许研究白色物质（WM）微观结构。DTI具有巨大的潜力，有助于了解病理生理学的白色物质和延迟成熟。此外，它能够非侵入性地追踪肿瘤患者的WM通路，也有助于诊断患有非病灶性疾病的患者。然而，DTI仍然存在技术缺陷，随着磁场的增加，这些缺陷变得更加成问题。这是不幸的，因为增加的磁场强度提供了显著更高的SNR，这是SNR匮乏的方法（如DTI）迫切需要的。由于他们的尺寸和其他特定要求，特别是儿科患者将是DTI高场成像的主要受益者-特别是当与更强大的功能磁共振成像和结构成像相结合时，可以在这些更高的领域实现。在更高场使用DTI的障碍包括：FOV要求、缺乏合作、运动增加、非共振伪影增加、显著的RF不均匀性和RF能量沉积增加。目标-拟议项目的主要目标是通过新型采集/重建技术显著改善高场（即3 T和7 T）下的DTI，这些技术可减少失真、提高运动免疫力、减少RF沉积和翻转角变化，并提供更好的空间分辨率，从而实现改善的儿科和成人高场DTI。具体目标是开发和优化弥散张量短轴读出EPI（sr-EPI）的采集和重建方法（A.1），并通过将优化的sr-EPI DTI采样策略与并行发射相结合来研究和帮助重新点燃对7 T DTI的兴趣，以及通过添加多回波读出来进一步提高扫描效率（A.2）。预期向更高场强的发展，这些目标旨在为临床环境（3 T）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短时间成像的方法。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，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和扫描时间有效的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7 T上实施并行传输技术。与“精确”失真模型一起，这些B1/B 0校正方法理想地补充了sr-EPI的快速变体。通过添加RF重聚焦多刀片/盲读出，扫描效率将进一步提高。所有提出的采集和重建技术将在模拟和体模研究中进行优化。在这5年期间，将入组总计200例受试者（儿童和成人）进行广泛测试。最佳图像质量将由定量指标和人类观察员确定。 意义-我们相信这些目标的成功实现有望显着改善DTI，超越高视野和儿科患者，因此更大的整体效用的DTI。对WM和束投射的了解可以为攻击白色物质的几种疾病的病理生理学提供重要的见解，并进一步了解有和没有WM障碍的儿童的特定神经发育轨迹。我们的研究工作的成功将是非常有价值的，因为它将建立在高领域的基础方法框架，进一步临床重点研究和基础神经科学研究。

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.