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空间和时间分辨率的改进。超过空间和时间分辨率的现有限制的两个最有前途的手段包括使用高磁场强度，一方面，和使用射频（RF）线圈阵列的加速并行成像，另一方面。预计这些办法的结合将产生特别的协同增效作用。并行成像缩短的采集时间可用于克服与高场研究相关的一些挑战，包括敏感性伪影和比吸收比（SAR）约束。同时，在高场强下增加的自旋极化导致增加的信噪比（SNR），这可以实现比在较低场下可能的更高的加速度。最近预计会有更多的协同作用。最终的固有SNR的计算显示出显着的改善，可实现的并行成像性能与增加的场强，以上和超出增加的自旋极化的影响。这些改进可追溯到减小的RF波长和在高场强下改进的RF聚焦能力。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RF系统设计的一些传统范例。该提案的主要目标是解决所需的RF设计的理论和实践问题，以接近计算的最佳并行成像性能作为场强的函数。我们建议评估各种去耦策略的有效性，建立实际线圈尺寸的具体基准，并建立原型多元素阵列能够在1.5T和3 T的数量级加速度。在这个项目的过程中，我们还将建立基本原则，通过这些原则，这些设计可以扩展到更高的场强，以便在空间和时间分辨率方面得到更大的改进。具体研究目的如下：1.使用8单元测试阵列，评估单元间解耦策略对基线SNR的影响，并实施产生最佳SNR的策略。2.使用计划安装在Beth Israel Deaconess Medical Center的新32接收器系统，根据场强确定32元件阵列的最小实用线圈尺寸。3.根据具体目标1和2的结果，分别构造了适用于1.5T和3 T二维加速度的32元阵列，并对阵列性能进行了定量比较。4.将二维加速度与这些阵列结合使用，以实现心脏、乳腺、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.从梯度线圈设计中调整靶场方法，以建立稳健的并行成像阵列设计，该设计在较高场强下近似计算出的最佳行为。

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.