Technical Development of Multinuclear Sodium Magnetic Resonance Imaging

过去 30 年的工程进步使磁共振成像 (MRI) 成为人体非侵入性研究的强大成像方式。常规临床 MRI 测量水中氢 (1H) 原子核的信号。然而，借助适当的硬件和成像技术，MRI 还可以从其他原子核（例如钠 (23Na) 和钾 (39K)）获取信号，这些离子可能比普遍存在的水分子更能特异性地反映组织损伤和疾病的情况。对钠进行成像的能力可以测量骨关节炎中的软骨退化情况，骨关节炎是一种影响数百万加拿大人的衰弱疾病。钾是大脑功能的关键离子，但缺乏在人脑中测量钾的方法。这笔赠款的目的是开发高灵敏度射频 (RF) 线圈硬件（例如灵敏相控阵）和成像方法，以实现软骨 (23Na) 或大脑 (39K) 中这些细胞核的定量成像。该提案建立在我们十年来的钠 MRI 研究的基础上，该研究产生了世界领先的人类大脑和膝盖图像（过去 5 年由 NSERC 资助）。 钠（和钾）MRI 非常具有挑战性，因为组织中的浓度低、磁回比小、信号衰减快、自旋物理复杂，并且需要特定于核的硬件和最佳方法。我们之前对膝关节软骨的钠 MRI 研究侧重于最佳采集策略的设计，但我们仅使用标准体积射频线圈。然而，由许多小型局部元件组成的更复杂、更灵敏的相控阵射频线圈可以显着提高信噪比，从而在图像分辨率和量化方面产生重大收益。虽然相控阵技术现已成为常规 1H MRI 的标准技术，但钠 MRI 仍处于起步阶段，不仅需要针对膝盖进行探索，还需要针对其他身体部位进行探索，例如手腕、脚踝、臀部和脊柱（这些部位的软骨也受到骨关节炎的影响）。钾比钠需要克服更大的技术挑战，而且最近只有两份关于人脑中钾 MRI 的初步报告。 新型 MRI 硬件和方法将由学员设计、模拟、构建、编程、测试和发布。该开发将针对“三重强度”高场 4.7T MRI，以实现信号的重大增益。我们假设我们的 MRI 技术进步将能够准确测量软骨中的钠和大脑中的钾。 具体目标： 1) 开发相控阵仅接收钠射频线圈和双频 (23Na/1H) 可解调同心发射体线圈，用于对膝盖、脚踝和手腕进行成像。在这种情况下，体积线圈提供均匀的激励，而相控阵提供高接收灵敏度。将探索使用反向旋转电流线圈元件同时从相控阵和体积线圈接收的能力，以促进与相控阵元件的空间变化的射频灵敏度分布相关的加速图像强度校正。 2) 开发用于脊柱和髋部钠 MRI 的收发双频相控阵射频线圈，其中均匀体积激励对于钠不可行。相关目标是开发和优化多线圈元件传输以实现均匀激励。 3）开发人脑定量钾MRI。 5年后，我们将开发出新型多核射频线圈硬件和优化的MRI采集，以实现（i）四肢、髋部和脊柱软骨中的钠（骨关节炎影响的关键结构）和（ii）大脑中的钾（大脑代谢的新型生物标志物）成像。

Engineering advances over the last 30 years have made magnetic resonance imaging (MRI) a powerful imaging modality for the non-invasive investigation of the human body. Routine clinical MRI measures signal from the hydrogen (1H) nuclei in water. However, with the appropriate hardware and imaging techniques, MRI can also acquire signal from other nuclei such as sodium (23Na) and potassium (39K), ions which may be more specific to aspects of tissue injury and disease than the ubiquitous water molecule. The ability to image sodium can provide a measure of cartilage degradation in osteoarthritis, a debilitating condition affecting millions of Canadians. Potassium is a key ion in brain function, but methods to measure it in human brain are lacking. The purpose of this grant is to develop highly sensitive radiofrequency (RF) coil hardware (e.g. sensitive phased arrays) and imaging methodology to enable quantitative imaging of these nuclei either in cartilage (23Na) or brain (39K). This proposal builds on our decade’s worth of sodium MRI research, which produced world-leading images of human brain and then knee (funded over last 5 years by NSERC). Sodium (and potassium) MRI is very challenging because of low concentration in tissue, small magnetogyric ratio, rapid signal decay, complex spin physics, and the need for nucleus-specific hardware and optimal methods. Our previous sodium MRI research on cartilage of the knee focused on the design of optimal acquisition strategies, but we used only standard volume RF coils. However, more complex and sensitive phased-array RF coils, which consist of many small localized elements, can dramatically increase signal-to-noise ratio and thus yield major gains in image resolution and quantification. While phased-array technology is now standard for regular 1H MRI, it is in its infancy for sodium MRI and needs to be explored not only for knee, but also for other body regions such as wrist, ankle, hip, and spine (where cartilage is also affected by osteoarthritis). Potassium has even greater technical challenges to overcome than sodium, and there are only two recent preliminary reports of potassium MRI in human brain. The novel MRI hardware and methods will be designed, simulated, constructed, programmed, tested, and published by the trainees. The developments will be on a ‘triple strength’ high field 4.7T MRI to enable major gains in signal. We hypothesize that our technical MRI advances will enable the accurate and precise measurement of sodium in cartilage and potassium in brain. Specific Aims: 1) To develop phased-array receive-only sodium RF coils and dual-frequency (23Na/1H) detunable, concentric transmit volume coils for imaging the knee, ankle, and wrist. In this case the volume coil provides uniform excitation and the phased-array provides high receive sensitivity. The capability for simultaneous reception from both the phased-array and volume coils using counter-rotating-current coil elements will be explored to facilitate accelerated image intensity correction related to the spatially varying RF sensitivity profiles of the phased-array elements. 2) To develop transceive dual-frequency phased-array RF coils for sodium MRI of the spine and hip, where uniform volume excitation is not feasible for sodium. An associated aim is to develop and optimize multiple coil element transmission for uniform excitation. 3) To develop quantitative potassium MRI of human brain. After 5 years, we will have developed novel multi-nuclear radiofrequency coil hardware and optimized MRI acquisition to enable imaging of (i) sodium in cartilage of the extremities, hip, and spine which are key structures affected in osteoarthritis, and (ii) potassium in the brain, a novel biomarker of brain metabolism.