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Low field MRI is safer and more cost effective than the high field MRI. One of the inherent problems of low field MRI is its low signal-to-noise ratio or sensitivity. In this work, we introduce a multimodal surface coil technique for signal excitation and reception to improve the RF magnetic field (B 1) efficiency and potentially improve MR sensitivity. The proposed multimodal surface coil consists of multiple identical resonators that are electromagnetically coupled to form a multimodal resonator. The field distribution of its lowest frequency mode is suitable for MR imaging applications. The prototype multimodal surface coils are built, and the performance is investigated and validated through numerical simulation, standard RF measurements and tests, and comparison with the conventional surface coil at low fields. Our results show that the B 1 efficiency of the multimodal surface coil outperforms that of the conventional surface coil which is known to offer the highest B 1 efficiency among all coil categories, i.e., volume coil, half-volume coil and surface coil. In addition, in low-field MRI, the required low-frequency coils often use large value capacitance to achieve the low resonant frequency which makes frequency tuning difficult. The proposed multimodal surface coil can be conveniently tuned to the required low frequency for low-field MRI with significantly reduced capacitance value, demonstrating excellent low-frequency operation capability over the conventional surface coil. [ABSTRACT FROM AUTHOR]

In vivo phosphorus-31 (31P) magnetic resonance spectroscopy (MRS) imaging (MRSI) is an important non-invasive imaging tool for studying cerebral energy metabolism, intracellular nicotinamide adenine dinucleotide (NAD) and redox ratio, and mitochondrial function. However, it is challenging to achieve high signal-to-noise ratio (SNR) 31P MRS/MRSI results owing to low phosphorus metabolites concentration and low phosphorous gyromagnetic ratio ( γ ). Many works have demonstrated that ultrahigh field (UHF) could significantly improve the 31P-MRS SNR. However, there is a lack of studies of the 31P MRSI SNR in the 10.5 Tesla (T) human scanner. In this study, we designed and constructed a novel 31P-1H dual-frequency loop-dipole probe that can operate at both 7T and 10.5T for a quantitative comparison of 31P MRSI SNR between the two magnetic fields, taking into account the RF coil B1 fields (RF coil receive and transmit fields) and relaxation times. We found that the SNR of the 31P MRS signal is 1.5 times higher at 10.5T as compared to 7T, and the power dependence of SNR on magnetic field strength (B0) is 1.9. [ABSTRACT FROM AUTHOR]

Temporomandibular Joint Magnetic Resonance Imaging (TMJ MRI) is crucial for diagnosing temporomandibular disorders (TMDs). This study advances the use of inductively coupled wireless coils to enhance imaging quality in TMJ MRI. After investigating multiple wireless resonator configurations, including a 1-loop design with a loop diameter of 9 cm, a 2-loop design with each loop having a diameter of 7 cm, and a 3-loop design with each loop having a diameter of 5 cm, our findings indicate that the 3-loop configuration achieves the optimal signal-to-noise ratio (SNR), surpassing other wireless arrays. Bilateral deployment of wireless coils further amplifies SNR, enabling superior visualization of TMJ structures, particularly with the 3-loop design. This cost-effective and comfortable solution, featuring a detunable design, eliminates the need for system parameter adjustments. The study indicates broad adaptability across MRI platforms, enhancing TMJ imaging for routine clinical diagnostics of TMDs. [ABSTRACT FROM AUTHOR]

Recent developments in the field of radiofrequency (RF) coils for magnetic resonance imaging (MRI) offer flexible and patient-friendly solutions. Previously, we demonstrated a proof-of-concept single-element stretchable coil design based on liquid metal and a self-tuning smart geometry. In this work, we numerically analyze and experimentally study a multi-channel stretchable coil array and demonstrate its application in dynamic knee imaging. We also compare our flexible coil array to a commonly used commercial rigid coil array. Our numerical analysis shows that the proposed coil array maintains its resonance frequency (<1% variation) and sensitivity (<6%) at various stretching configurations from 0% to 30%. We experimentally demonstrate that the signal-to-noise ratio (SNR) of the acquired MRI images is improved by up to four times with the stretchable coil array due to its conformal and therefore tight-fitting nature. This stretchable array allows for dynamic knee imaging at different flexion angles, infeasible with traditional, rigid coil arrays. These findings are significant as they address the limitations of current rigid coil technology, offering a solution that enhances patient comfort and image quality, particularly in applications requiring dynamic imaging. [ABSTRACT FROM AUTHOR]

Purpose: There are 118 known elements. Nearly all of them have NMR active isotopes and at least 39 different nuclei have biological relevance. Despite this, most of today's MRI is based on only one nucleus—1H. To facilitate imaging all potential nuclei, we present a single transmit coil able to excite arbitrary nuclei in human‐scale MRI. Theory and Methods: We present a completely new type of RF coil, the Any‐nucleus Distributed Active Programmable Transmit Coil (ADAPT Coil), with fast switches integrated into the structure of the coil to allow it to operate at any relevant frequency. This coil eliminates the need for the expensive traditional RF amplifier by directly converting direct current (DC) power into RF magnetic fields with frequencies chosen by digital control signals sent to the switches. Semiconductor switch imperfections are overcome by segmenting the coil. Results: Circuit simulations demonstrated the effectiveness of the ADAPT Coil approach, and a 9 cm diameter surface ADAPT Coil was implemented. Using the ADAPT Coil, 1H, 23Na, 2H, and 13C phantom images were acquired, and 1H and 23Na ex vivo images were acquired. To excite different nuclei, only digital control signals were changed, which can be programmed in real time. Conclusion: The ADAPT Coil presents a low‐cost, scalable, and efficient method for exciting arbitrary nuclei in human‐scale MRI. This coil concept provides further opportunities for scaling, programmability, lowering coil costs, lowering dead‐time, streamlining multinuclear MRI workflows, and enabling the study of dozens of biologically relevant nuclei. [ABSTRACT FROM AUTHOR]

Radio Frequency (RF) coils are necessary for MRI machines and are critical in improving image quality. Due to numerous research efforts in RF coil development, birdcage and surface coils are the most commonly used in clinical applications to enhance medical imaging quality. This article introduces a new surface-type RF coil that is improved by its proximity to the scanned object, boosting its effectiveness. Contrary to past research that examined RF coils operating at one resonant frequency, this study presents a microstrip-based surface RF coil created for dual-frequency use at 64 MHz and 128 MHz, matching the Larmor frequencies for 1.5 T and 3 T MRI machines. The coil was carefully planned, tested, and created, with simulations including a human body model to assess the distribution of the $B_{1}$ field and signal-to-noise ratio (SNR), both essential for assessing the RF coil’s performance in the coronal plane. A tuning circuit was created and tested to maximize resonance at specific frequencies. In contrast, a matching circuit was designed to improve power transfer efficiency between the signal generator and the coil. The suggested RF coil was enhanced by incorporating these circuits, improving overall performance. Both the suggested surface-type microstrip RF coil, which includes tuning and matching circuits, effectively functions at 64 MHz and 128 MHz, as shown by both simulation and experimental results, making it a viable clinical option.

Magnetic resonance imaging (MRI) is an invaluable tool for the diagnosis and study of brain function. Central to the MRI system, the radio frequency (RF) coil plays a dual role: stimulating spins and receiving the MR signal, enabling the generation of detailed images from inside the body. Compared to using linear polarised (LP) methods, the efficiency of the RF coil can be improved by leveraging circular polarised (CP) driving methods, which operate with at least two elements and 90° phase input difference. Coil efficiency can also be improved with the use of a multi-channel phased array receive-only coils, as they provide higher SNR compared to volume coils. Generally, all elements of phased array coils operate in LP mode. However, if the LP elements are replaced by dimension-matched CP elements, the SNR of the phased array coil can be further increased. This study introduces a novel single-channel butterfly coil uniquely capable of operating in CP mode. This is achieved by operating the CP element with asymmetrical tuning and a split resonance peak. The performance of the single-channel CP butterfly coil was evaluated in simulations and MR measurements, and the results were compared to those from single-channel LP coils. The results show that the single-channel CP butterfly coil is a good solution for increasing SNR in phased array receive-only coils.

Inductively coupled radiofrequency (RF) coils are an inexpensive and simple method to realize wireless RF coils in magnetic resonance imaging (MRI), which can significantly ease the MRI scan setup and improve patient comfort because they do not require bulky components such as cables, baluns, preamplifiers, and connectors. However, volume‐type wireless coils are typically operated in transmit/receive mode because detuning such coils is much more challenging due to their complex structure and multiple resonant modes. Meanwhile, adding too many detuning circuits to a wireless coil would decrease the coil's quality factor, impair the signal‐to‐noise ratio, and increase the cost. In this work, we proposed, constructed, and tested a novel wireless volume coil based on the Litzcage design for 1.5‐T head imaging. Being an inductively coupled coil, it has a much simpler structure, resulting in a lighter weight and less bulky design. Despite its simpler structure, it exhibits comparable imaging performance with a commercial receive array, providing an alternative to conventional wired coils with a high cost and complex structure. The unique figure‐of‐8 conductor pattern within the rungs ensures that the proposed wireless Litzcage can be efficiently detuned with minimal detuning circuits. [ABSTRACT FROM AUTHOR]

The design of radiofrequency (RF) coils is crucial for ultra-high field (UHF) magnetic resonance imaging (MRI) systems. To analyze RF coils, various numerical methods, such as finite-difference time-domain (FDTD) and method of moments (MoM), are usually adopted. In this paper, we present a novel hybrid approach that combines a two-dimensional (2D) FDTD with a three-dimensional (3D) MoM to analyze MRI RF problems. In our algorithm, the MoM is utilized for calculating the coil current, and FDTD is assigned for solving the electromagnetic (EM) fields in the imaging region. The hybrid method achieves superior efficiency and acceptable accuracy than using either method individually. To validate the hybrid method, we analyze an ellipse coil loaded with a uniform phantom and a realistic human head model, with the objective of tailoring the magnetic field intensity by adding a multilayer dielectric pad (DP). The results show an improvement in the magnetic field after optimizing the DP configuration. These simulation studies indicate the potential of the new numerical method for the design and analysis of RF systems for ultra-high field applications. [ABSTRACT FROM AUTHOR]

Cerebral blood flow (CBF) is a critical physiological parameter of brain health, and it can be non-invasively measured with arterial spin labeling (ASL) MRI. In this study, we evaluated and optimized whole-brain, high-resolution ASL as an alternative to the low-resolution ASL employed in the routine assessment of CBF in both healthy participants and patients. Two high-resolution protocols (i.e., pCASL and FAIR-Q2TIPS (PASL) with 2 mm isotropic voxels) were compared to a default clinical pCASL protocol (3.4 x 3.4 x 4 mm³), all of whom had an acquisition time of ≈5 min. We assessed the impact of high-resolution acquisition on reducing partial voluming and improving sensitivity to the perfusion signal, and evaluated the effectiveness of z-deblurring on the ASL data. We compared the quality of whole-brain ASL acquired using three available head coils with differing number of receive channels (i.e., 20, 32, and 64ch). We found that using higher coil counts (32 and 64ch coils as compared to 20ch) offers improved signal-to-noise ratio (SNR) and acceleration capabilities that are beneficial for ASL imaging at 3 Tesla (3 T). The inherent reduction in partial voluming effects with higher resolution acquisitions improves the resolving power of perfusion without impacting the sensitivity. In conclusion, our results suggest that high-resolution ASL (2 to 2.5 mm isotropic voxels) has the potential to become a new standard for perfusion imaging at 3 T and increase its adoption into clinical research and cognitive neuroscience applications. [ABSTRACT FROM AUTHOR]

Pulsed electromagnetic field (PEMF) stimulation is a non-invasive therapeutic modality that has been employed in a variety of applications, including skin wound healing, tissue regeneration, blood vessel regeneration, repair of nonunion bone fractures, and dental treatment. Currently, the potential side effects of electromagnetic fields on tissues have not been comprehensively explored, despite their established therapeutic benefits. In this study, we examined the side effects of PEMF devices on whole-body tissues using simulations. The electromagnetic field simulation software CST Studio Suite was utilized, and an RF coil that could output different frequencies (100 Hz, 100 kHz, and 27 MHz) and magnetic fields (0.25 mT, 0.5, and 1 mT) was designed for the purpose of simulations. A realistic rat model, available from the CST library, was employed. Using the Debye equations according to the relevant frequency value, the electrical and thermal properties of the rat were calculated, and the simulation was carried out in two stages: EM and thermal analysis. The specific absorption rate in the tissues with EM simulation and the temperature distribution in the tissues with thermal analysis were examined. The effects created by the PEMF device at different frequencies and magnetic field intensities were presented comparatively. According to the results, the highest SAR value was observed for three different magnetic field intensities at a frequency of 27 MHz, resulting in a temperature difference of 0.7 °C. This study aims to determine the EM effects on rats in a simulated environment according to different frequencies and magnetic field values, as well as to determine whether the thermal effects created can produce a side response. By doing so, it will be possible to improve noninvasive clinical PEMF devices and provide additional information about the interaction of electromagnetic fields with tissues. [ABSTRACT FROM AUTHOR]

Cerebral blood flow (CBF) is a critical physiological parameter of brain health, and it can be non-invasively measured with arterial spin labeling (ASL) MRI. In this study, we evaluated and optimized whole-brain, high-resolution ASL as an alternative to the low-resolution ASL employed in the routine assessment of CBF in both healthy participants and patients. Two high-resolution protocols (i.e., pCASL and FAIR-Q2TIPS (PASL) with 2 mm isotropic voxels) were compared to a default clinical pCASL protocol (3.4 × 3.4 × 4 mm3), all of whom had an acquisition time of ≈ 5 min. We assessed the impact of high-resolution acquisition on reducing partial voluming and improving sensitivity to the perfusion signal, and evaluated the effectiveness of z-deblurring on the ASL data. We compared the quality of whole-brain ASL acquired using three available head coils with differing number of receive channels (i.e., 20, 32, and 64ch). We found that using higher coil counts (32 and 64ch coils as compared to 20ch) offers improved signal-to-noise ratio (SNR) and acceleration capabilities that are beneficial for ASL imaging at 3 Tesla (3 T). The inherent reduction in partial voluming effects with higher resolution acquisitions improves the resolving power of perfusion without impacting the sensitivity. In conclusion, our results suggest that high-resolution ASL (2 to 2.5 mm isotropic voxels) has the potential to become a new standard for perfusion imaging at 3 T and increase its adoption into clinical research and cognitive neuroscience applications.

Background: Low-field open magnetic resonance imaging (MRI) systems, typically operating at magnetic field strengths below 1 Tesla, has greatly expanded the accessibility of MRI technology to meet a wide range of patient needs. However, the inherent challenges of low-field MRI, such as limited signal-to-noise ratios and limited availability of dedicated radiofrequency (RF) coils, have prompted the need for innovative coil designs that can improve imaging quality and diagnostic capabilities., Purpose: In response to these challenges, we introduce the coupled stack-up volume coil, a novel RF coil design that addresses the shortcomings of conventional birdcage in the context of low-field open MRI., Methods: The proposed coupled stack-up volume coil design utilizes a unique architecture that optimizes both transmit/receive efficiency and RF field homogeneity and offers the advantage of a simple design and construction, making it a practical and feasible solution for low-field MRI applications. This paper presents a comprehensive exploration of the theoretical framework, design considerations, and experimental validation of this innovative coil design., Results: We demonstrate the superior performance of the coupled stack-up volume coil in achieving 47.7% higher transmit/receive efficiency and 68% more uniform magnetic field distribution compared to traditional birdcage coils in electromagnetic simulations. Bench tests results show that the B1 field efficiency of coupled stack-up volume coil is 57.3% higher compared with that of conventional birdcage coil., Conclusions: The proposed coupled stack-up volume coil outperforms the conventional birdcage coil in terms of B1 efficiency, imaging coverage, and low-frequency operation capability. This design provides a robust and simple solution to low-field MR RF coil design.

In this paper, we propose a metamaterial-inspired RF coil structure based on a multiple split-ring resonator (MSRR) for 1.5T MRI. An additional component that enables to enhance the magnetic field of RF coil is proposed. This novel component is incorporated an array of split-rings and a central feature combined with square and circular rings (SC). By aligning the component with the split-ring resonator (SRR) in a coplanar arrangement, we derive a compact MSRR equipped with the SC structure (SC MSRR). We analyze the effect of different numbers of split rings within the component and the distance from the feed coil on gain of the magnetic field. The results indicate that the proposed metamaterial-inspired structure can effectively improve the near-field properties of the coil. The proposed SC MSRR has enhanced B 1 − field strength effectively and keeps a lower specific absorption rate (SAR) level in the field of view (FOV), resulting in a significant increase in SAR efficiency and received sensitivity. Compared with the conventional SRR surface coil, the peak B 1 − field strength can be enhanced by 3.15 times in the case of using SC MSRR, the peak SAR can be reduced by 20.14 % and the peak SAR efficiency can be improved 3.60 times. In addition, the proposed 4-channel head array consisting of SC MSRRs efficiently generates a higher quality B 1 − field compared to the standard head birdcage coil. The high directivity of the metamaterial-inspired structure allows for good isolation between ports/channels. The high compactness and excellent performance of the SC MSRR prove that it can be an efficient candidate for the surface coil and high density array. This approach provides a new practical way to combine RF coils with metamaterials for MRI applications. • Metamaterial-inspired SC MSRR structure for 1.5T MRI. ∙ Compared to SRR RF coil, SC MSRR offer higher receiver sensitivity, magnetic field penetration, and SAR efficiency. ∙ The SC MSRR with high directivity and good self-decoupling characteristics between channels. ∙ The SC MSRR element and array are more compact and have superior performance compared to other MRI enhancement devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cost-Effective Enhancement: Proposes a simple and low-cost wireless resonator to improve TMJ MRI. • Innovative Coil Design: Utilizes a local receive array as the primary coil for enhanced imaging quality. • Distortion-Free Imaging: Introduces a receive-only wireless coil, ensuring no transmit field distortion. • Clinical Adaptability: Facilitates seamless integration into clinical applications without the need for coil parameter modifications. • Parallel Imaging capability: Preserves parallel imaging capability in the primary receive array. MRI is essential for evaluating and diagnosing various conditions affecting the temporomandibular joint (TMJ) and surrounding structures, as it provides highly detailed images that enable healthcare professionals to assess the joints and surroundings in great detail. While commercial MRI scanners typically come equipped with basic receive coils, such as the head receive array, RF coils tailored for specialized applications like TMJ MRI must be obtained separately. Consequently, TMJ MRI scans are often conducted using the head receive array, yet this configuration proves suboptimal due to the lack of specialized coils. In this study, we introduce a simple, low-cost, and easy-to-reproduce wireless resonator insert to enhance the quality of TMJ MRI at 1.5 T. The wireless resonator shows a significant improvement in signal-to-noise ratio (SNR) and noticeably better imaging quality than the head array alone configuration in both phantom and in vivo images. [ABSTRACT FROM AUTHOR]

A direct comparison of the impact of RF coil design under specific absorption rate andB1+rmslimitations are investigated and quantified using RF coils of different geometries and topologies at 64 MHz and 128 MHz. The RF-induced in vivo electric field and power deposition of a 50 cm long pacemaker and 55 cm long deep brain stimulator (DBS) are evaluated within two anatomical models exposed with these RF coils. The associated uncertainty is quantified and analyzed under a fixedB1+rmsincident and normal operating mode. For a fixedB1+rmsincident, the in vivo incident field shows a much higher uncertainty (>5.6 dB) to the RF coil diameter compared to other design parameters (e.g. <2.2 dB for coil length and topology), while the associated uncertainty reduced greatly (e.g. <1.5 dB) under normal operating mode exposure. Similar uncertainties are observed in the power deposition near the pacemaker and DBS electrode. Compared to the normal operating mode, applying a fixedB1+rmsfield to the untested implant will lead to a large variation in the induced incident and power deposition of the implant, as a result, a larger safe margin when different coil designs (e.g. coil diameter) are considered., (Creative Commons Attribution license.)