Multinuclear Magnetic Resonance Imaging Research Articles

Frequency-independent dual-tuned cable traps for multi-nuclear MRI and MRS

Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) of non-proton nuclei (X-nuclei) typically require additional proton imaging for anatomical reference and B0 shimming. Therefore, two RF systems exist, necessitating cable traps to block the unwanted common-mode current at both Larmor frequencies of 1H and X-nuclei. This study introduces a frequency-independent dual-tuned cable trap that combines a standard solenoid cable trap with a float solenoid trap to independently tune high and low frequencies without compromising performance. The methods involved theoretical analysis, electromagnetic simulations, and bench tests. Two design approaches were evaluated: a float cable trap for 1H, a non-float cable trap for X-nuclei, and vice versa. Results showed that the design with the float trap for X-nuclei and non-float for 1H had superior performance, with high common-mode current suppression ability at both frequencies. Bench tests confirmed these findings, demonstrating effectiveness across various static fields and X-nuclei. The proposed frequency-independent dual-tuned cable trap provides a compact and efficient solution for multinuclear MRI and MRS, enhancing safety, image quality, and flexibility.

Simultaneous multinuclear MRI via a single RF channel

Magnetic resonance imaging (MRI) stands as one of the most powerful noninvasive and non-destructive imaging techniques, finding extensive utility in medical and industrial applications. Its ability to acquire signals from multiple nuclei grants it additional levels of strength by providing multi-dimensional datasets of the object under test. However, this typically requires dedicated hardware to detect each nucleus. In this paper, we report on the use of a digital lock-in amplifier to perform simultaneous multi-nuclear MRI with a single physical radio frequency (RF) channel. While we showcase this concept by demonstrating the results of fully parallel (TX and RX) 1H and 19F MRI images, we emphasize that it is not limited to two nuclei but can accommodate more nuclei with no extra cost on the hardware or scan time. The scalability is virtually unlimited, constrained only by the processing speed of the digital unit. Furthermore, we demonstrate that the quality of parallel imaging with SNR of 54 is comparable to the commercial single channel with SNR of 43. Thus with no reduction in imaging quality, the proposed concept promises a tremendous reduction in scan time, system complexity, and hardware costs.

Advances in COPD imaging using CT and MRI: linkage with lung physiology and clinical outcomes.

Recent years have witnessed major advances in lung imaging in patients with COPD. These include significant refinements in images obtained by computed tomography (CT) scans together with the introduction of new techniques and software that aim for obtaining the best image whilst using the lowest possible radiation dose. Magnetic resonance imaging (MRI) has also emerged as a useful radiation-free tool in assessing structural and more importantly functional derangements in patients with well-established COPD and smokers without COPD, even before the existence of overt changes in resting physiological lung function tests. Together, CT and MRI now allow objective quantification and assessment of structural changes within the airways, lung parenchyma and pulmonary vessels. Furthermore, CT and MRI can now provide objective assessments of regional lung ventilation and perfusion, and multinuclear MRI provides further insight into gas exchange; this can help in structured decisions regarding treatment plans. These advances in chest imaging techniques have brought new insights into our understanding of disease pathophysiology and characterising different disease phenotypes. The present review discusses, in detail, the advances in lung imaging in patients with COPD and how structural and functional imaging are linked with common resting physiological tests and important clinical outcomes.

Troubleshooting and Quality Assurance in Hyperpolarized Xenon Magnetic Resonance Imaging: Tools for High-Quality Image Acquisition.

Hyperpolarized (HP) xenon magnetic resonance imaging (129Xe MRI) is a recently federal drug administration (FDA)-approved imaging modality that produces high-resolution images of an inhaled breath of xenon gas for investigation of lung function. However, implementing 129Xe MRI is uniquely challenging as it requires specialized hardware and equipment for hyperpolarization, procurement of xenon imaging coils and coil software, development and compilation of multinuclear MR imaging sequences, and reconstruction/analysis of acquired data. Without proper expertise, these tasks can be daunting, and failure to acquire high-quality images can befrustrating, and expensive. Here, we present some quality control (QC) protocols, troubleshooting practices, and helpful tools for129Xe MRI sites, which may aid in the acquisition of optimized, high-quality data and accurate results. The discussion will begin with an overview of the process for implementing HP 129Xe MRI, including requirements for a hyperpolarizer lab, the combination of 129Xe MRI coil hardware/software, data acquisition and sequence considerations, data structures, k-space and image properties, and measured signal and noise characteristics. Within each of these necessary steps lies opportunities for errors, challenges, and unfavorable occurrences leading to poor image quality or failed imaging, and this presentation aims to address some of the more commonly encountered issues. In particular, identification and characterization of anomalous noise patterns in acquired data are necessary to avoid image artifacts and low-quality images; examples will be given, and mitigation strategies will be discussed. We aim to make the 129Xe MRI implementation process easier for new sites while providing some guidelines and strategies for real-time troubleshooting.

Adaptable Dual-Tuned Optically Controlled On-Coil RF Power Amplifier for MRI.

An adaptable optically controlled RF power amplifier (RFPA) is presented for direct implementation on the Magnetic Resonance Imaging (MRI) transmit coil. Operation at 1H and multiple X-nuclei frequencies for 7T MRI was demonstrated through the automated tuning of an effective voltage-modulated inductor located in the gate driver circuit of the FET switches in the different amplification stages. Through this automated tuning the amplifier can be adapted from the control to operate at the selected 1H and X-nuclei frequency in a multinuclear MRI study. Bench and MRI data acquired with the adaptable dual-tuned on-coil RFPA is presented. This technology should allow a simpler, more efficient and versatile implementation of the multinuclear multichannel MRI hardware. Ultimately, to extend the research on MRI detectable nuclei that can provide new insights about healthy and diseased tissue.

Cardiac and intramuscular adaptations following short-term exercise prehabilitation in unfit patients scheduled to undergo hepatic or pancreatic surgery (CIRCULATE): study protocol of a multi-nuclear magnetic resonance imaging study

Cardiac and intramuscular adaptations following short-term exercise prehabilitation in unfit patients scheduled to undergo hepatic or pancreatic surgery (CIRCULATE): study protocol of a multi-nuclear magnetic resonance imaging study

Multinuclear MR and MRI study of lithium-ion cells using a variable field magnet and a fixed frequency RF probe

An exploratory multinuclear magnetic resonance (MR) and magnetic resonance imaging (MRI) study was performed on lithium-ion battery cells with 7Li, 19F, and 1H measurements. A variable field superconducting magnet with a fixed frequency parallel-plate radiofrequency (RF) probe was employed in the study. The magnetic field was changed to set the resonance frequency of each nucleus to the fixed RF probe frequency of 33.7 MHz. Two cartridge-like lithium-ion cells, with graphite anodes and LiNi0.5Mn0.3Co0.2O2 (NMC) cathodes, were interrogated. One cell was pristine, and one was charged to a cell voltage of 4.2 V. The results presented demonstrate the great potential of the variable field magnet approach in multinuclear measurement of lithium-ion batteries. These methods open the door for developing faster and simpler methods for detecting, quantifying, and interpreting MR and MRI data from lithium-ion and other batteries.

MR-Nucleomics: The study of pathological cellular processes with multinuclear magnetic resonance spectroscopy and imaging in vivo.

Clinical medicine has experienced a rapid development in recent decades, during which therapies targeting specific cellular signaling pathways, or specific cell surface receptors, have been increasingly adopted. While these developments in clinical medicine call for improved precision in diagnosis and treatment monitoring, modern medical imaging methods are restricted mainly to anatomical imaging, lagging behind the requirements of precision medicine. Although positron emission tomography and single photon emission computed tomography have been used clinically for studies of metabolism, their applications have been limited by the exposure risk to ionizing radiation, the subsequent limitation in repeated and longitudinal studies, and the incapability in assessing downstream metabolism. Magnetic resonance spectroscopy (MRS) or spectroscopic imaging (MRSI) are, in theory, capable of assessing molecular activities in vivo, although they are often limited by sensitivity. Here, we review some recent developments in MRS and MRSI of multiple nuclei that have potential as molecular imaging tools in the clinic.

Multinuclear MRI Reveals Early Efficacy of Stem Cell Therapy in Stroke.

Compromised adult human mesenchymal stem cells (hMSC) can impair cell therapy efficacy and further reverse ischemic recovery. However, in vitro assays require extended passage to characterize cells, limiting rapid assessment for therapeutic potency. Multinuclear magnetic resonance imaging and spectroscopy (MRI/S) provides near real-time feedback on disease progression and tissue recovery. Applied to ischemic stroke, 23Na MRI evaluates treatment efficacy within 24h after middle cerebral artery occlusion, showing recovery of sodium homeostasis and lesion reduction in specimens treated with hMSC while 1H MRS identifies reduction in lactate levels. This combined metric was confirmed by evaluating treatment groups receiving healthy or compromised hMSC versus vehicle (sham saline injection) over 21days. Behavioral tests to assess functional recovery and cell analysis for immunomodulatory and macrophage activity to detect hMSC potency confirm MR findings. Clinically, these MR metrics may prove critical to early evaluations of therapeutic efficacy and overall stroke recovery.

Dual-Tuned Lattice Balun for Multi-Nuclear MRI and MRS.

Balun or trap circuits are critical components for suppressing common-mode currents flowing on the outer conductors of coaxial cables in RF coil systems for Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS). Common-mode currents affect coils' tuning and matching, induce losses, pick up extra noise from the surrounding environment, lead to undesired cross-talk, and cause safety concerns in animal and human imaging. First proposed for microwave antenna applications, the Lattice balun has been widely used in MRI coils. It has a small footprint and can be easily integrated with coil tuning/matching circuits. However, the Lattice balun is typically a single-tuned circuit and cannot be used for multi-nuclear MRI and MRS with two RF frequencies. This work describes a dual-tuned Lattice balun design that is suitable for multi-nuclear MRI/MRS. It was first analyzed theoretically to derive component values. RF circuit simulations were then performed to validate the theoretical analysis and provide guidance for practical construction. Based on the simulation results, a dual-tuned balun circuit was built for 7T 1H/23Na MRI and bench tested. The fabricated dual-tuned balun exhibits superior performance at the Larmor frequencies of both 1H and 23Na, with less than 0.15 dB insertion loss and better than 17 dB common-mode rejection ratio at both frequencies.

Design and Comparison of Different Types of Dual-Frequency Matching Networks Used in Double-Tuned Coils for Multinuclear Magnetic Resonance Imaging and Spectroscopy

Multi-resonant RF coils are often used in multinuclear MR imaging and/or spectroscopy experiments, and a large variety of strategies for multi-tuning coils exist. However, designing a multi-tuned coil with good performance is challenging, and improvements in sensitivity are always desirable - particularly on the X-nucleus coil due to the intrinsically lower MR sensitivity of non-proton nuclei. In this work, various dual-frequency matching networks in double-tuned coils are compared, and their effect on the coil performance is investigated. Four different dual-frequency matching networks were designed and constructed with frequency-splitting or -blocking traps, which enable exploration of both proton-1 ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H) and sodium-23 ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> Na) nuclei. Two single-frequency matching networks were also built without any additional lossy components as a reference, and their matchings were set to either the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H or the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> Na frequency. The initial evaluation was conducted on the bench using a network analyser to examine the scattering (S)-parameters and quality factors of the connected RF coils. The performance of the attached matching networks was then further evaluated by measuring the corresponding signal-to-noise ratio (SNR) based on images obtained at a 7 T clinical MRI scanner. It was found that even though the tuning and matching conditions were nearly impeccable in the S-parameters, the actual <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H SNR decreased significantly due to the inserted traps, whereas the SNRs of the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> Na frequency were nearly maintained with the added traps and the losses were much less. The dual-frequency matching networks create additional sensitivity loss, which is dependent on the actual implementation of the matching circuit. This is in agreement with previously reported results associated with the evaluation of inserted double-tuning traps for RF coils.

Multinuclear MRI to disentangle intracellular sodium concentration and extracellular volume fraction in breast cancer

The purpose of this work was to develop a novel method to disentangle the intra- and extracellular components of the total sodium concentration (TSC) in breast cancer from a combination of proton (^{1}H) and sodium (^{23}hbox {Na}) magnetic resonance imaging (MRI) measurements. To do so, TSC is expressed as function of the intracellular sodium concentration (hbox {C}_{text {IC}}), extracellular volume fraction (ECV) and the water fraction (WF) based on a three-compartment model of the tissue. TSC is measured from ^{23}hbox {Na} MRI, ECV is calculated from baseline and post-contrast ^{1}H hbox {T}_{{1}} maps, while WF is measured with a ^{1}H chemical shift technique. hbox {C}_{text {IC}} is then extrapolated from the model. Proof-of-concept was demonstrated in three healthy subjects and two patients with triple negative breast cancer. In both patients, TSC was two to threefold higher in the tumor than in normal tissue. This alteration mainly resulted from increased hbox {C}_{text {IC}} (sim 30 mM), which was sim 130% greater than in healthy conditions (10–15 mM) while the ECV was within the expected range of physiological values (0.2–0.25). Multinuclear MRI shows promise for disentangling hbox {C}_{text {IC}} and ECV by taking advantage of complementary ^{1}H and ^{23}hbox {Na} measurements.

Multi-Tuned Radiofrequency Coil Using Microfluidically Tunable Capacitor for Magnetic Resonance Imaging/Spectroscopy at 7-Tesla

Multi-nuclear magnetic resonance imaging and spectroscopy are considered valuable tools due to their capability of diagnosis and monitoring of several diseases. They require multi-nuclear Radiofrequency coils in order to interrogate the proton (1H) and other nuclei (X-nuclei) in the human body. Such coils provide anatomical images by acquiring (1H) spectra and metabolites information by acquiring spectra of X-nuclei. In addition, the high signal received from proton (1H) is used for B0 shimming purposes. However, the signal strength for these X-nuclei is too low. Hence, the signal-to-noise-ratio is low. The main advantages of using multinuclear Radiofrequency coils are that they speed up the imaging process and reduce the spatial positioning error that might arise when replacing the Radiofrequency coil in order to perform imaging of different nuclei. In addition, comfortable environment will be provided for patients by avoiding any inconvenience of moving out and asking to replace the coils. In this paper, a multi-tunable microstrip transmission line Radiofrequency coil has been designed by using microfluidically tunable Radiofrequency capacitor. This capacitor offers a wide range of capacitance tuning which extends between Cmin=1.76 pF and Cmax=48.7 pF. Hence, a wide range of resonant frequencies (fmin=75 MHz - fmax=298 MHz) can be offered by this coil in order to excite several nuclei at a field strength of 7-Tesla.

Multinuclear magnetic resonance imaging in biomedical experiments

The detection of nuclei other than protons can significantly enhance the opportunities of MRI method. Thereby one of the most promising nuclei in this field is fluorine-19. We showed that it is possible to visualize lungs, gastrointestinal tract and inflammation regions by 19F MRI without complicated and expensive specific technics. Moreover, the use of other nuclei in multinuclear applications is also possible and it is a promising direction in this field.

3nd International Conference and Young Scientist School “Magnetic Resonance Imaging in Biomedical Research”

A.V. Naumova 1,2, M.Yu. Khodanovich1,2, V.L. Yarnykh1,21 Department of Radiology, University of Washington, Seattle, WA, USA2 Research Institute of Biology and Biophysics, Tomsk State University, Tomsk, RussiaThe Third International Conference and Young Scientist School “Magnetic Resonance Imaging in Biomedical Research” was held in Novosibirsk, Russia, on November 24-26, 2016. The Conference was held within the framework of the International Congress on Clinical and Translational Neuroimaging organized by the International Tomography Center of the SB RAS, Institute of Medicine and Psychology at Novosibirsk State University (NSU), Institute of Cytology and Genetics of the SB RAS, and Tomsk State University (TSU).The Conference focused on magnetic resonance imaging (MRI) applications for biomedical research. The main goal was to bring together major scientists, clinical researchers and developers of new MRI techniques to bridge the gap between clinical/research needs and advanced technological solutions. The Conference encouraged research and development in basic and clinical MR science and its application in health care. It also had an educational purpose to promote understanding of cutting-edge MR developments. The Conference provided an opportunity for researchers and clinicians to present their recent theoretical developments, practical applications, and to discuss acute problems.The program of the Conference was divided into three main topics. The first day of the Conference was devoted to educational lectures on the fundamentals of MRI physics and image acquisition/reconstruction techniques including recent developments in quantitative MRI. The second day focused on developments and applications of new contrast agents. Multinuclear and spectroscopic acquisitions as well as functional MRI were presented on the third day of the Conference.We would like to highlight the main developments presented at the Conference and introduce the prominent speakers. The keynote speaker of the conference Dr. Vasily Yarnykh (University of Washington, Seattle, USA) demonstrated a method of macromolecular proton fraction and its application in clinical and preclinical studies. Professor Yury Pirogov (Lomonosov Moscow State University) presented development of multinuclear magnetic resonance imaging in biomedical experiments. Dr. Marina Khodanovich (Tomsk State University) described histological validation of macromolecular proton fraction mapping on the model of cuprizone-induced demyelination.We express our thanks to the scientific committee, the local organizing committee and Tomsk State University for giving the opportunity to share scientific ideas and up-to-date developments at the Conference, and the Russian Science Foundation (project № 14-45-00040) and Biovitrum Ltd. for financial support.

Design and implementation of a simple multinuclear MRI system for ultra high-field imaging of animals

Non-proton MRI has recently garnered gathering interest with the increased availability of ultra high-field MRI system. Assuming the availability of a broadband RF amplifier, performing multinuclear MR experiments essentially requires additional hardware, such as an RF resonator and a T/R switch for each nucleus. A double- or triple-resonant RF probe is typically constructed using traps or PIN-diode circuits, but this approach degrades the signal-to-noise ratio (SNR) and image quality compared to a single-resonant coil and this is a limiting factor.In this work, we have designed the required hardware for multinuclear MR imaging experiments employing six single-resonant coil sets and a purpose-built animal bed; these have been implemented into a home-integrated 9.4T preclinical MRI scanner. System capabilities are demonstrated by distinguishing concentration differences and sensitivity of X-nuclei imaging and spectroscopy without SNR penalty for any nuclei, no subject interruption and no degradation of the static shim conditions.

Design of a multimodal (1H/23Na MR/CT) anthropomorphic thorax phantom

ObjectivesThis work proposes a modular, anthropomorphic MR and CT thorax phantom that enables the comparison of experimental studies for quantitative evaluation of deformable, multimodal image registration algorithms and realistic multi-nuclear MR imaging techniques. MethodsA human thorax phantom was developed with insertable modules representing lung, liver, ribs and additional tracking spheres. The quality of human tissue mimicking characteristics was evaluated for 1H and 23Na MR as well as CT imaging. The position of landmarks in the lung lobes was tracked during CT image acquisition at several positions during breathing cycles. 1H MR measurements of the liver were repeated after seven months to determine long term stability. ResultsThe modules possess HU, T1 and T2 values comparable to human tissues (lung module: −756±148HU, artificial ribs: 218±56HU (low CaCO3 concentration) and 339±121 (high CaCO3 concentration), liver module: T1=790±28ms, T2=65±1ms). Motion analysis showed that the landmarks in the lung lobes follow a 3D trajectory similar to human breathing motion. The tracking spheres are well detectable in both CT and MRI. The parameters of the tracking spheres can be adjusted in the following ranges to result in a distinct signal: HU values from 150 to 900HU, T1 relaxation time from 550ms to 2000ms, T2 relaxation time from 40ms to 200ms. ConclusionThe presented anthropomorphic multimodal thorax phantom fulfills the demands of a simple, inexpensive system with interchangeable components. In future, the modular design allows for complementing the present set up with additional modules focusing on specific research targets such as perfusion studies, 23Na MR quantification experiments and an increasing level of complexity for motion studies.

Multinuclear Magnetic Resonance Imaging and NMR Spectroscopy in Biomedical Investigations

Biomedical investigations with small animals using 0.5-T and 7-T MRI scanners adjusted on the Larmor frequencies of different nuclei 1H, 2H, 11B, 13C, 19F, 23Na, 31P, 35Cl are described. Experiments on registration of signals 19F from the fluorocarbons injected in laboratory animals are discussed. They give presentation on the application of fluorocarbon compounds as blood substitutes and contrasting preparations in MRI diagnostics. A blood substitute product fluorocarbon Perfluoranum® has shown effectiveness in oxygen delivery to the tissues of living organisms, and cardioprotective effect which does not depend on the patient's blood group. Inclusion of paramagnetic atoms (gadolinium, iron, etc.) to the Perfluoranum® chemical formula creates a new compounds with high MRI contrast efficiencies at Larmor frequencies of protons so and fluorine-19 nuclei.

Modular Coils with Low Hydrogen Content Especially for MRI of Dry Solids.

IntroductionRecent advances have enabled fast magnetic resonance imaging (MRI) of solid materials. This development has opened up new applications for MRI, but, at the same time, uncovered new challenges. Previously, MRI-invisible materials like the housing of MRI detection coils are now readily depicted and either cause artifacts or lead to a decreased image resolution. In this contribution, we present versatile, multi-nuclear single and dual-tune MRI coils that stand out by (1) a low hydrogen content for high-resolution MRI of dry solids without artifacts; (2) a modular approach with exchangeable inductors of variable volumes to optimally enclose the given object; (3) low cost and low manufacturing effort that is associated with the modular approach; (4) accurate sample placement in the coil outside of the bore, and (5) a wide, single- or dual-tune frequency range that covers several nuclei and enables multinuclear MRI without moving the sample.Materials and MethodsThe inductors of the coils were constructed from self-supporting copper sheets to avoid all plastic materials within or around the resonator. The components that were mounted at a distance from the inductor, including the circuit board, coaxial cable and holder were manufactured from polytetrafluoroethylene.Results and ConclusionResidual hydrogen signal was sufficiently well suppressed to allow 1H-MRI of dry solids with a minimum field of view that was smaller than the sensitive volume of the coil. The SNR was found to be comparable but somewhat lower with respect to commercial, proton-rich quadrature coils, and higher with respect to a linearly-polarized commercial coil. The potential of the setup presented was exemplified by 1H / 23Na high-resolution zero echo time (ZTE) MRI of a model solution and a dried human molar at 9.4 T. A full 3D image dataset of the tooth was obtained, rich in contrast and similar to the resolution of standard cone-beam computed tomography.

Investigation of the distribution of heavy nuclei in laboratory animals using multinuclear magnetic resonance imaging

The use of multinuclear magnetic resonance imaging (MRI) for investigating the distribution of deuterium and perfluorocarbons in laboratory rats is considered. This technique is implementable at any MRI scanner that allows its transmitter and receiver circuitry to be tuned to the necessary Larmor frequencies. It is shown that multinuclear MRI opens up broad prospects for biological and medical in vivo research.