High-performance high-field parallel MRI

描述(由申请人提供)： 磁共振成像的临床和研究应用继续要求提高空间和时间分辨率。超过现有空间和时间分辨率限制的两种最有希望的方法包括一方面使用高磁场强度，另一方面使用射频(RF)线圈阵列加速并行成像。预计这些方法的组合将产生特别的协同作用。并行成像缩短的采集时间可能被用来克服与高场研究相关的一些挑战，包括磁化率伪影和特定吸收率(SAR)限制。同时，在高场强下增加的自旋极化会导致信噪比(SNR)的增加，这可以实现比在低场下更高的加速度。最近有人预测会有更多的协同效应。对最终本征信噪比的计算表明，在自旋极化增强的影响之外，随着场强的增加，可实现的并行成像性能显著改善。这些改进归因于射频波长的减少和高场强下射频聚焦能力的提高。要充分利用并行成像和高场强之间的协同效应，需要改变线圈阵列和射频系统设计的一些传统范例。这项提议的主要目标是解决射频设计所需的理论和实践问题，以接近计算出的最佳并行成像性能作为场强的函数。我们建议评估各种解耦策略的有效性，为实际线圈尺寸建立具体的基准，并建立能够在1.5T和3T下产生数量级加速度的多单元阵列原型。在项目过程中，我们还将确立将这些设计扩展到更高场强的基本原则，以便在空间和时间分辨率方面取得更大的改进。研究的具体目标如下：1.使用8元测试阵列，评估单元间解耦策略对基线信噪比的影响，并实施产生最佳信噪比的策略。2.使用计划安装在贝丝以色列女执事医疗中心的新的32-接收器系统，建立32单元阵列的最小实用线圈尺寸，作为场强的函数。3.基于特定目标1和2的结果，分别构建了适用于1.5T和3T二维加速的32元阵列，并对阵列性能进行了定量比较。4.将二维加速与这些阵列结合使用，以实现心脏、乳房、身体和大脑成像应用中常用的一组成像序列的空间和/或时间分辨率的数量级增加。5.采用来自梯度线圈设计的靶场方法来建立稳健的并行成像阵列设计，其近似于在较高场强下计算的最优行为。

DESCRIPTION (provided by applicant): Clinical and research applications of magnetic resonance imaging continue to demand improvements in spatial and temporal resolution. Two of the most promising means of exceeding existing limits on spatial and temporal resolution include the use of high magnetic field strengths, on the one hand, and the use of radiofrequency (RF) coil arrays for accelerated parallel imaging, on the other. Particular synergies are expected for combinations of these approaches. Shortened acquisition times resulting from parallel imaging may be used to overcome some of the challenges associated with high-field studies, including susceptibility artifacts and specific absorption ratio (SAR) constraints. Meanwhile, increased spin polarization at high field strength results in increased signal to noise ratio (SNR), which can enable higher accelerations than would be possible at lower fields. Additional synergies have recently been predicted. Calculations of ultimate intrinsic SNR show marked improvements in achievable parallel imaging performance with increasing field strength, above and beyond the effects of increased spin polarization. These improvements have been traced to the reduced RF wavelength and improved RF focusing capability at high field strength. Access to the full benefits of this synergy between parallel imaging and high field strength will require changes in some of the traditional paradigms for coil array and RF system design. The broad goal of this proposal is to solve the theoretical and practical issues of RF design required in order to approach the computed optimal parallel imaging performance as a function of field strength. We propose to evaluate the efficacy of various decoupling strategies, to establish concrete benchmarks for practical coil sizes, and to build prototype many-element arrays capable of order-of-magnitude accelerations at 1.5T and 3T. In the course of the project, we will also establish the basic principles by which these designs may be extended to higher field strengths in order to yield still greater improvements in spatial and temporal resolution. Specific Aims of the proposed research are as follows: 1. Using 8-element test arrays, assess the impact of inter-element decoupling strategies upon baseline SNR, and implement the strategy that yields the best SNR. 2. Use new 32-receiver systems scheduled to be installed at Beth Israel Deaconess Medical Center to establish the smallest practical coil size for 32-element arrays as a function of field strength. 3. Based on the results from Specific Aims 1 and 2, construct 32-element arrays suitable for two-dimensional accelerations at 1.5T and at 3T, respectively, and perform quantitative comparisons of array performance. 4. Use two-dimensional acceleration in combination with these arrays to achieve order-of-magnitude increases in spatial and/or temporal resolution for a set of imaging sequences used commonly in cardiac, breast, body, and brain imaging applications. 5. Adapt target field methods from gradient coil design to establish robust parallel imaging array designs that approximate the computed optimum behavior at higher field strength.