Technical Development of Multinuclear Sodium Magnetic Resonance Imaging

在过去的30年里，工程技术的进步使磁共振成像（MRI）成为一种强大的成像模式，用于人体的非侵入性研究。常规临床MRI测量水中氢（1H）核的信号。然而，通过适当的硬件和成像技术，MRI还可以从其他核（如钠（23 Na）和钾（39 K））中获取信号，这些离子可能比无处不在的水分子更具体地针对组织损伤和疾病的各个方面。钠成像的能力可以提供骨关节炎软骨退化的测量，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，但缺乏测量人脑中钾的方法。该资助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（23 Na）或大脑（39 K）中这些核的定量成像。该提案建立在我们十年来钠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是非常具有挑战性的，因为在组织中的浓度低，磁旋比小，信号衰减快，自旋物理复杂，需要核特定的硬件和最佳方法。我们之前对膝关节软骨的钠MRI研究主要集中在最佳采集策略的设计上，但我们仅使用了标准体积RF线圈。然而，由许多小的局部元件组成的更复杂和更灵敏的相控阵RF线圈可以显著提高信噪比，从而在图像分辨率和量化方面产生重大增益。虽然相控阵技术现在是常规1H MRI的标准，但钠MRI仍处于起步阶段，不仅需要探索膝盖，还需要探索其他身体区域，如手腕，脚踝，臀部和脊柱（软骨也受骨关节炎影响）。钾比钠更需要克服技术挑战，最近只有两份关于钾在人脑中的MRI初步报告。 新的MRI硬件和方法将由受训者设计、模拟、构造、编程、测试和发布。这些发展将是一个“三重强度”的高场4.7T MRI，以实现信号的主要增益。我们假设我们的MRI技术进步将能够准确和精确地测量软骨中的钠和大脑中的钾。 具体目标： 1)开发用于膝关节、踝关节和腕关节成像的相控阵仅接收钠RF线圈和双频（23 Na/1H）可解调同心发射体积线圈。在这种情况下，体积线圈提供均匀的激励，相控阵列提供高接收灵敏度。同时接收从相控阵列和体积线圈使用反向旋转电流线圈元件的能力将被探索，以促进加速图像强度校正相关的相控阵列元件的空间变化的RF灵敏度曲线。 2)开发用于脊柱和髋关节钠MRI的双频率相控阵RF线圈，其中钠的均匀体积激励不可行。相关的目的是开发和优化用于均匀激励的多线圈元件传输。 3)目的：建立人脑钾离子定量MRI。 5年后，我们将开发新型多核射频线圈硬件并优化MRI采集，以实现（i）四肢、髋关节和脊柱软骨中的钠（骨关节炎中受影响的关键结构）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.