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)成为对人体进行非侵入性研究的一种强大的成像手段。常规的临床核磁共振测量水中氢(1H)核的信号。然而，在适当的硬件和成像技术下，MRI也可以从其他核团获取信号，如钠(23Na)和钾(39K)，这些离子可能比无处不在的水分子更具组织损伤和疾病方面的特异性。钠的成像能力可以提供骨关节炎软骨退化的衡量标准，骨关节炎是一种影响数百万加拿大人的衰弱疾病。钾是大脑功能中的关键离子，但缺乏在人脑中测量它的方法。这笔赠款的目的是开发高灵敏度的射频(RF)线圈硬件(例如灵敏相控阵)和成像方法，以便能够对软骨(23Na)或脑(39K)中的这些核进行定量成像。这一建议建立在我们十年来钠核磁共振研究的价值基础上，该研究产生了世界领先的人脑图像，然后是膝盖图像(过去5年由NSERC资助)。 钠(和钾)磁共振成像非常具有挑战性，因为它在组织中的浓度低，磁致伸缩比小，信号衰减快，自旋物理复杂，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核磁共振研究集中在设计最佳采集策略，但我们只使用标准体积的射频线圈。然而，更复杂和更灵敏的相控阵射频线圈，由许多小的局部化元件组成，可以显著提高信噪比，从而在图像分辨率和量化方面产生巨大的收益。虽然相控阵技术现在是常规1H MRI的标准，但对于钠类MRI来说，它还处于初级阶段，不仅需要探索膝盖，还需要探索身体的其他部位，如腕部、脚踝、髋部和脊柱(这些部位的软骨也会受到骨关节炎的影响)。钾要克服的技术挑战甚至比钠更大，最近只有两份关于钾在人脑中进行核磁共振的初步报告。 新的MRI硬件和方法将由学员设计、模拟、构造、编程、测试和发布。开发的将是一个三倍强度的4.7T高场磁共振成像，以实现信号的重大增强。我们假设，我们的核磁共振技术进步将使我们能够准确和精确地测量软骨中的钠和脑中的钾。 具体目标： 1)开发相控阵只接收钠射频线圈和双频(23Na/1H)可调谐同心发射体积线圈，用于膝关节、脚踝和手腕的成像。在这种情况下，体积线圈提供均匀的激励，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从相控阵和体积线圈同时接收的能力，以促进与相控阵元件的空间变化的RF灵敏度分布相关的加速图像强度校正。 2)研制用于脊柱和髋部钠核磁共振成像的收发双频相控阵射频线圈，在钠离子不能均匀体积激发的情况下。一个相关的目标是开发和优化用于均匀激励的多线圈元件传输。 3)开展人脑定量钾磁共振成像研究。 5年后，我们将开发新的多核射频线圈硬件和优化的MRI采集，以实现(I)肢体、髋关节和脊柱软骨中的钠，这是骨关节炎的关键结构，以及(Ii)脑中的钾，一种新的脑代谢生物标志物。

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.