X‐nuclei imaging: Current state, technical challenges, and future directions

Abstract

1H imaging is concerned with contrast generation among anatomically distinct soft tissues. X‐nuclei imaging, on the other hand, aims to reveal the underlying changes in the physiological processes on a cellular level. Advanced clinical MR hardware systems improved 1H image quality and simultaneously enabled X‐nuclei imaging. Adaptation of 1H methods and optimization of both sequence design and postprocessing protocols launched X‐nuclei imaging past feasibility studies and into clinical studies. This review outlines the current state of X‐nuclei MRI, with the focus on 23Na, 35Cl, 39K, and 17O. Currently, various aspects of technical challenges limit the possibilities of clinical X‐nuclei MRI applications. To address these challenges, quintessential physical and technical concepts behind different applications are presented, and the advantages and drawbacks are delineated. The working process for methods such as quantification and multiquantum imaging is shown step‐by‐step. Clinical examples are provided to underline the potential value of X‐nuclei imaging in multifaceted areas of application. In conclusion, the scope of the latest technical advance is outlined, and suggestions to overcome the most fundamental hurdles on the way into clinical routine by leveraging the full potential of X‐nuclei imaging are presented. Level of Evidence: 1 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:355–376.

Efficient 23Na triple‐quantum signal imaging on clinical scanners: Cartesian imaging of single and triple‐quantum 23Na (CRISTINA)

“…Multiquantum sodium ( 23 Na) NMR was first been investigated and described 3 decades ago 1–5 . Recently, technological advances have led to a revival of 23 Na MRI, with a particular interest in the potential to link multiquantum 23 Na MRI to underlying pathophysiological pathways 6–9 . In standard 23 Na imaging experiments, detection of the single‐quantum (SQ) transition is performed directly after an excitation with similar approaches to conventional proton MRI.…”

“…[1][2][3][4][5] Recently, technological advances have led to a revival of 23 Na MRI, with a particular interest in the potential to link multiquantum 23 Na MRI to underlying pathophysiological pathways. [6][7][8][9] In standard 23 Na imaging experiments, detection of the single-quantum (SQ) transition is performed directly after an excitation with similar approaches to conventional proton MRI. To exploit the potential of the spin 3/2 nuclei, multiquantum coherence (MQC) signals are built by coherence transfer and combined over multiple acquisitions using RF phase cycling.…”

A Review on the RF Coil Designs and Trends for Ultra High Field Magnetic Resonance Imaging

“…MR images are primarily obtained from 1 H protons, which are highly abundant in the human body; however, MRI also allows us to scan other types of nuclei, such as 23 Na, 31 P, and 13 C (108,109). However, these other nuclei are in low concentration in the body, so it is difficult to obtain MR signals and images with enough S/N s. Nevertheless, the use of MRI of x-nuclei is gaining increasing interest because stronger magnets allow the reception of other nuclei, such as 23 Na, 31 P, and 13 C. x-nuclei have a different Larmor frequency compared to 1 H, so it is necessary to develop RF coils that can receive and transmit signals at the appropriate frequency.…”

23Na MRI in ischemic stroke: Acquisition time reduction using postprocessing with convolutional neural networks

“…15,16 However, 23 Na MRI faces technical challenges that have prevented its clinical establishment to date. 17,18 The most prominent hurdle is the long acquisition times due to low signal-to-noise ratio (SNR) and biexponential signal decay. 23 Na MRI signal in the human brain is approximately 12,000 times lower than the 1 H signal.…”