Volume Coil Research Articles

A 32-channel receive array coil for bilateral breast imaging and spectroscopy at 7T.

This work describes the construction and evaluation of a bilateral 32-channel receive array for breast imaging at 7T. The receive array consisted of 32 receive coils, placed on two 3D-printed hemispherical formers. Each side of the receive array consisted of 16 receive loops, each loop having a corresponding detachable board with match/tune capacitors, active detuning circuitry, and a balun. Coil performance was evaluated on homogeneous canola oil phantoms using a Philips Achieva 7T system. Array coil performance was compared with a bilateral forced current excitation volume coil in transmit/receive mode and with a previously reported 16-channel unilateral coil with a similar design. The 32-channel array had an increase in average SNR throughout both phantoms by a factor of five as compared with the volume coil, with SNR increases up to 10 times along the periphery and three times in the center. Noise measurements showed low interelement noise correlation (average: 5.4%; maximum: 16.8%). Geometry factor maps were acquired for various acceleration factors and showed mean geometry factors<1.2, for combined acceleration factors of up to six. The improvements achieved demonstrate the clear potential for use in dynamic contrast-enhanced or diffusion-weighted MR studies, while maintaining diagnostically relevant spatial and temporal resolutions.

Multi-site benchmarking of clinical 13C RF coils at 3T

A quality assurance protocol for RF coils is proposed, which can be used for volume (Tx/Rx) and surface (Rx) coils. Following this protocol, a benchmarking of seven coils (from three different MR sites) dedicated to 13C MRI at 3T is reported. Coil performance is particularly important for 3T MRI at the 13C frequency, since the coil-to-sample noise ratio is typically high. The coils are evaluated experimentally using the proposed protocol based on MR spectroscopic imaging performed with two different phantoms: one head-shaped, and one with cylindrical shape and nearly twice the volume of the first one. To achieve an unbiased SNR comparison of volume and array coils, coil combination was done using sensitivity profiles extracted from the data. SNR, noise correlation matrices and example g-factor maps are reported. For globally calibrated, equal excitation angles, the measured SNR shows large differences for the volume coils of up to 115% at the phantom center for a head phantom. The arrays show lower differences in superficial SNR. The sample surface depth at which the volume coils outperform the arrays is estimated to 7 cm, and SNR furthest away from the coil surface is 28% lower for the best array compared to the best volume coil. A broad set of coils for 13C at 3T have been benchmarked. The results reported, and the method used to benchmark them, should guide the 13C community to choose the most suitable coil for a given experiment.

Development and optimization of a receive-only surface array with purely geometrical decoupling for rat brain MRI at 2 T

Magnetic resonance imaging (MRI) experiments on small animals, as well as in humans, require specific radiofrequency (RF) coil designs in order to maximize field homogeneity during excitation and signal-to-noise ratio (SNR) during reception. Therefore, the use of dedicated transmit-only and receive-only coil geometries has been preferred as standard technology configuration. Among the receive coil geometries, the surface coil has been widely used to increase the SNR in localized regions of interest. With the advent of MRI-phased arrays, the high sensitivity of surface coils can be achieved in extended regions, further allowing parallel imaging acquisition methodologies to accelerate acquisition time. This work describes the development and characterization of a two-channel receive-only RF coil set specifically designed for MRI acquisition of rat brain in a 2 T system for neuroscience studies. We have developed and compared the performance of one common surface coil with a two-channel phased array with purely geometric decoupling between coil elements (i.e., without using low input impedance preamplifiers), both actively detuned during reception and having exactly the same dimensions. The results have shown that the single-channel surface coil achieved up to 5 times higher SNR at 5 mm depth compared to a volume coil commonly used for rat brain MRI in our laboratory, while the two-channel array achieved 4 times higher SNR at the same depth, with the additional advantage of producing an extended area with higher sensitivity. In vivo brain images of anesthetized rats confirmed the SNR gain for both receive-only single-channel surface coil and two-channel array in comparison with a volume coil. We have verified that only using the partial overlapping technique does not provide sufficient isolation to eliminate mutual coupling interaction between elements, since residual coupling can still affect the coil performance.

Design and Experiment of a Reconfigurable Magnetic Resonance Coupling Wireless Power Transmission System

Magnetic resonance coupling wireless power transmission (WPT) provides a safe and efficient power supply for small household appliances and implanted devices, but the tolerance of the transmission distance is poor. To improve the robustness of the transmission distance of the magnetic resonance WPT system, a method of using a reconfigurable helical coil array is proposed. Compared with the traditional four-coil structure of the same volume, different source and load coils are selected under distinct distance conditions. The coupling coefficient between the coils is changed to increase the stability of transmission efficiency and distance. To avoid the mechanical movement, all source and load coils have been adjusted at fixed position. Moreover, a control method is introduced to achieve coil switching. The experimental results show that the transmission distance of the proposed system is increased to 1.75 times of the coil diameter, while the efficiency remains above 70%.

Offset-tuned Bilateral-side Inductively Coupled RF Coils for Preclinical MRI at 15.2 T

A small coverage of magnetic flux density (B₁) and its inhomogeneity are intrinsic problems of conventional surface coils. Therefore, offset-tuned bilateral-side inductively coupled radiofrequency (RF) coils have been specifically designed to overcome these problems. Herein, we proposed bilateral-sided wireless coils for improving the B1-field uniformity by simultaneously adding a supplemental secondary coil (s-coil) to the primary coil (pcoil) in the orthogonal direction. The offset-tuned frequency of the s-coil was evaluated and compared from 0 to +60 MHz with a +10 MHz interval at the Larmor frequency of the p-coil. Using mathematical EM modeling, we optimized the +60-MHz offset-tuned s-coil at 15.2 T. Thus, a combined coil configuration with p-coil of 655 MHz and two s-coils of 710 MHz was obtained. This combined coil configuration can overcome the B₁-field inhomogeneity of p-coils in 15.2 T small animal magnetic resonance scanner and can be extended to overcome the volume coil array inhomogeneity.

Novel imaging technology and procedures for studying brain function in preadolescent awake marmosets

BackgroundNovel imaging technology and procedures were developed to study brain function in preadolescent awake marmosets never exposed to anesthesia. MethodsA radiofrequency transmit and receive, head only volume coil was designed and integrated into a holding system. An acclimation procedure was developed without the use of anesthesia or sedation that allowed for awake imaging. Preadolescent 8-month old male and female marmosets were imaged for resting state BOLD functional connectivity to assess the status of the default mode network. Levels of reactivity during acclimation sessions and behavioral stress following imaging were assessed. ResultsData on functional coupling in the default mode network suggest the organization of connectivity to the prefrontal cortex is not fully developed at 8 months of age. The stress associated with the imaging procedure is comparable to that observed when marmosets are removed from their home cage and temporarily isolated from the family. Comparison to other methodsThe design of the radiofrequency coil provides B1 homogeneity across the entire brain without signal drop off. The unique design of the head cradle obviates the need for any stabilizing surgery, ear bars or bite bar and could be adapted to any size marmoset. The acclimation requires no anesthesia or sedation at any time in the early life of the developing marmoset, a condition that better reflects the human experience. ConclusionA method is provided for imaging functional activity in the brain of fully awake preadolescent marmosets without any history of anesthesia or sedation.

Assessment of alternative divertor configurations as an exhaust solution for DEMO

Plasma exhaust has been identified as a major challenge towards the realisation of magnetic confinement fusion. To mitigate the risk that the single null divertor (SND) with a high radiation fraction in the scrape-of-layer (SOL) adopted for ITER will not extrapolate to a DEMO reactor, the EUROfusion consortium is assessing potential benefits and engineering challenges of alternative divertor configurations. Alternative configurations that could be readily adopted in a DEMO design include the X divertor (XD), the Super-X divertor (SXD), the Snowflake divertor (SFD) and the double null divertor (DND). The flux flaring towards the divertor target of the XD is limited by the minimum grazing angle at the target set by gaps and misalignments. The characteristic increase of the target radius in the SXD is a trade-off with the increased TF coil volume, but, ultimately, also limited by forces onto coils. Engineering constraints also limit XD and SXD characteristics to the outer divertor leg with a solution for the inner leg requiring up-down symmetric configurations. Capital cost increases with respect to a SND configuration are largest for SXD and SFD, which require both significantly more poloidal field coil conductors and in the case of the SXD also more toroidal field coil conductors. Boundary models with increasing degrees of complexity have been used to predict the beneficial effect of the alternative configurations on exhaust performance. While all alternative configurations should decrease the power that must be radiated in the outer divertor, only the DND and possibly the SFD also ease the radiation requirements in the inner divertor. These decreases of the radiation requirements are however expected to be small making the ability of alternative divertors to increase divertor radiation without excessive core performance degradation their main advantage. Initial 2D fluid modeling of argon seeding in XD and SFD configurations indicate such advantages over the SND, while results for SXD and DND are still pending. Additional improvements, expected from increased turbulence in the low poloidal field region of the SFD also remain to be verified. A more precise comparison with the SND as well as absolute quantitative predictions for all configurations requires more complete physics models that are currently only being developed.

Optimization of HTS Superconducting Solenoid Magnet Dimensions for Maximum Energy Density

Superconducting coil provides enormous amount of stored energy inside its magnetic field. Such a pure inductive superconducting (SC) coil can be designed for high power density or high energy density depending on coil dimensions and inductance based on the prerequisite of application. In this paper, a design procedure is developed to optimize dimensions of a high-temperature superconducting (HTS) coil to store maximum energy for a given length and critical properties of HTS tape. A minimum volume constraint (MVC) is developed to confine the variation of aspect ratios to keep the coil volume constant, thereby limiting the material, cryogenic and vacuum costs of HTS coil. A global optimum inner diameter is established by MVC, with which the optimum dimensions can be reached directly. Multiple constraints such as coil volume, stacked pancake arrangement, HTS tape length and mechanical properties are considered. The electrical, magnetic and mechanical parameters for different dimensions are then found by finite element method (FEM). The proposed method is applied to different lengths of 1G and 2G HTS tapes. The optimum dimensions of maximum stored energy are decided which gives a solenoid coil of maximum energy density.

Effective Excitation of Magnetoelectric Voltage Harmonics in a Ferromagnet–Piezoelectric Structure by Current Passing through the Magnetic Layer

The magnetoelectric (ME) effect in a planar amorphous ferromagnet–piezoelectric lead zirconate titanate (PZT) composite structure can be effectively excited by passing alternating current through the magnetic layer. The absence of demagnetizing (stray) field and the orientation of the exciting magnetic field perpendicular to the constant field allow this structure to generate the even harmonics of electric field with efficiency several times that for the ME effect produced by volume coils. It is established that the second harmonic amplitude is proportional to the piezomagnetic coefficient of the magnetic layer and the square amplitude of current and inversely proportional to the bias magnetic field.

Experimental Study on a Pulsation-enhanced Heat Transfer Device

The pulsation-enhanced heat transfer technology is introduced, and a volume coil heat exchanger is designed. A pulsation valve is installed at the heat exchanger outlet of the heat exchanger to pulsate the heat medium, and the same heat exchanger is subjected to pulsation and non-pulsation heat transfer tests. Based on the experiments, combined with the theory of pulsation-enhanced heat transfer technology, heat transfer capacity, heat flow, and convective heat transfer coefficient coefficients, the effective temperature difference, heat flow, and convective heat transfer coefficient of the heat exchanger at different pulse frequencies are analyzed. The relationship between the pulsation frequency of the heat transfer effect of the heat exchanger is obtained. The test results show that the heat exchanger has higher heat exchange efficiency when there is pulsation under the test conditions.

A practical realization of an artificial magnetic shield for preclinical birdcage RF coils

In the most of magnetic resonance imaging (MRI) systems, a conventional radiofrequency (RF) electric shield is typically placed around an RF volume coil to avoid the interaction with the other components of the system. Disadvantageously metal shields reduce the transmit efficiency of the RF coil as well as its receive sensitivity due to out-ofphase reflection of electromagnetic waves. In contrast, an ideal magnetic shield having high surface impedance provides in-phase reflection, which can be promising for improvement of RF coil’s performance. In this work, we propose an artificial magnetic shield based on a cylindrical miniaturized corrugated structure to improve characteristics of a small-animal birdcage coil at 7T. The coil was simulated in the presence of the metal and ideal magnetic shield as well as the proposed structure. The results demonstrate enhancement of the coil’s performance in the presence of the proposed shield, which is comparable with an ideal one.

Evaluation of RF interactions between a 3T birdcage transmit coil and transcranial magnetic stimulation coils using a realistically shaped head phantom.

Multichannel transcranial magnetic stimulation (TMS)1 is an emerging technology that allows multiple sites to be stimulated simultaneously or sequentially under electronic control without movement of the coils. A multichannel TMS/MRI head coil array for 3 Tesla is currently under development to mitigate challenges of concurrent TMS/fMRI as well as enable potential new applications. The influence of the multichannel TMS system on the MR image quality and safety must be carefully investigated. A standard birdcage volume coil for 3 Tesla systems was simulated using a commercial numerical electromagnetic solver. Two setups, consisting of 1) a MR-compatible TMS coil, and 2) a 3-axis TMS coil array, were simulated to quantify changes in the transmit field and the SAR. A realistically shaped homogeneous head model was used in the computations. The stimulation coils produced enhancements and attenuations on the transmit field with effects greater than 5% up to 2.4 cm and 3.3 cm under the scalp for the MR-compatible TMS coil and 3-axis TMS coil array, respectively. The 10 g-SAR distribution did not change significantly in either of the cases; however, the nominal SAR maximum locus was shifted between existing hot spots. The simulated variations found near the TMS coils indicate the possibility of inducing sequence-dependent image artefacts predominatly limited to the vicinity of the coil(s). However, we conclude that neither the MR-compatible commercial TMS coil nor the 3-axis TMS coil array siginificantly elevate SAR in the head or neck beyond accepted safety limits.

Measuring the link between cardiac mechanical function and metabolism during hyperpolarized 13C-pyruvate magnetic resonance experiments

PurposeThe goal of this study was to develop a methodology to investigate the relationship between contractile function and hyperpolarized (HP) [1-13C]pyruvate metabolism in a small animal model. To achieve sufficient signal from HP 13C compounds, HP 13C MRS/MRSI has required relatively large infusion volumes relative to the total blood volume in small animal models, which may affect cardiac function. MethodsEight female Sprague Dawley rats were imaged on a 4.7T scanner with a dual tuned 1H/13C volume coil. ECG and respiratory gated k-t spiral MRSI and an IDEAL based reconstruction to determine [1-13C]pyruvate metabolism in the myocardium. This was coupled with 1H cine MRI to determine ventricular volumes and mechanical function pre- and post-infusion of [1-13C]pyruvate. For comparison to the [1-13C]pyruvate experiments, three female Sprague Dawley rats were imaged with 1H cine MRI to determine myocardial function pre- and post-saline infusion. ResultsWe demonstrated significant changes in cardiac contractile function between pre- and post-infusion of [1-13C]pyruvate. Specifically, there was an increase in end-diastolic volume (EDV), stroke volume (SV), and ejection fraction (EF). Additionally, the ventricular vascular coupling ratio (VVCR) showed an improvement after [1-13C]pyruvate infusion, indicating increased systolic performance due to an increased arterial load. There was a moderate to strong relationship between the downstream metabolic conversion of pyruvate to bicarbonate and a strong relationship between the conversion of pyruvate to lactate and the cardiac mechanical function response. ConclusionThe infusion of [1-13C]pyruvate resulted in demonstrable increases in contractile function which was related to pyruvate conversion to bicarbonate and lactate. The combined effects of the infusion volume and inotropic effects of pyruvate metabolism likely explains the augmentation in myocardial mechanical function seen in these experiments. Given the relationship between pyruvate metabolism and contractile function observed in this study, this methodological approach may be utilized to better understand cardiac metabolic and functional remodeling in heart disease.

Эффективное возбуждение магнитоэлектрического эффекта в структуре ферромагнетик-пьезоэлектрик током через магнитный слой

The effective excitation of the magnetoelectric effect in a planar structure amorphous ferromagnet – piezoelectric lead zirconate titanate by alternating current flowing through the magnetic layer was demonstrated. Due to orientation of the exciting magnetic field perpendicular to the constant field and absence of demagnetization, the structure generates even voltage harmonics with efficiency, several times higher than the efficiency of excitation of the effect by volume coils. It was shown that the amplitude of the second harmonic is proportional to the piezomagnetic coefficient of the magnetic layer,increases quadratically with the amplitude of the current and decreases inversely with the biasing magnetic field

A new design of divided solenoid with high homogeneity based on linear programming

A novel divided solenoid with high homogeneity is designed through linear programming (LP) for actual guiding magnet application in high power microwave devices. During the LP process, current density, magnetic field homogeneity, and total volume of coils are set as variable, constraint condition, and objective function, respectively. The divided solenoid is designed after calculating current density in the available zone where the coil current exists. After comparing the electrical parameters and magnetic field distribution of the conventional and the new solenoid, it is concluded that the inhomogeneity of the new design is reduced from 10% to 0.7%, the central magnetic field is equal, and other factors are in the same range. The divided solenoid magnet designed by LP is able to achieve high uniformity by improving the winding process and mechanical structure, which also has strong generalization.

Impact of transvenous embolization via superior ophthalmic vein on reducing the total number of coils used for patients with cavernous sinus dural arteriovenous fistula.

Although transvenous embolization (TVE) via the superior ophthalmic vein (SOV) is adopted in treating cavernous sinus dural arteriovenous fistula (CS DAVF), its effect on the coil volume is rarely understood. The purpose of the study was to investigate if there is a difference in the total number of coils used and in patient safety when comparing two access strategies. We retrospectively reviewed charts for patients with CS DAVF treated with TVE between January 2008 and March 2018. The baseline patient characteristics, details of procedure, placed coils, and clinical results were compared. A total of 42 patients with CS DAVF were treated with the inferior petrosal sinus (IPS) (n = 32) or SOV (n = 10) approach. TVE via SOV showed a high success rate of 100% (10/10) by transfemoral access. The total number (23 versus 11; P < 0.001), length (159 versus 81cm; P = 0.003), and volume of placed coils (111 versus 46mm3; P = 0.005) were significantly lower in patients treated via SOV. Patients treated via SOV had significantly higher initial intrasinus pressure (49 versus 59mmHg; P = 0.022) obtained by microcatheters; however, no adverse events occurred related to elevated sinus pressure between both approaches. Procedural complications and cranial nerve palsy outcomes were not significantly different. In cases with a visualized pathway to the SOV, this approach should be preferred, in all other cases standard approach via the IPS should be used, even if it cannot be visualized.

Determination of Cefixime Using Batch, Cloud Point Extraction and Flow Injection as New Spectrophotometric Methods

Three simple, sensitive, selective, accurate and efficient spectrophotometric methodsfor determining cefixime in bulk drug and pharmaceutical formulations havedescribed. The first method involved conversion of NH 2 in cefixime to diazoniumsalt, which has coupled with Bisphenol A in an alkaline medium. The orange coloredproduct showed λ max at 490 nm and followed Beer's law over a concentration range of1-50 μg mL -1 , with molar absorptivity of 0.866×10 4 L.mol -1 .cm -1 and the detectionlimit was 0.157 μg.mL -1 . The second method involved pre-concentration of a traceamount of cefixime-azo dyes using cloud point extraction (CPE). The extracted drug-dye was spectrophotometrically measured at λ max 500. The constructed calibrationcurve to determine cefixime followed Beer’s law in a range of 0.25-6 μg.mL -1 , with acorrelation coefficient of 0.9998, molar absorptivity of 0.961×10 5 L.mol -1 .cm -1 andthe detection limit was equal to 0.031 μg.mL -1 . The pre-concentration factor was 25and distribution coefficient (D) was 314.03.A diazotization of the studied drug (cefixime) and its coupling with Bisphenol A wasstudied using a developed flow injection analysis method, based on the detection ofthe absorption of the diazotization product. Chemical and physical properties [ofwhat??] were studied to develop the suggested method and to determine the stabilityof the colored of product. A flow rate of 2.5 mL.min -1 , 50 cm reaction coil and 100μL sample volume were used to operate the system and the orange colored productwas detected at 490 nm. The proposed three methods were successfully applied todetermine cefixime in pharmaceutical formulation, where results were satisfactory

Dual-Tuned Monopole/Loop Coil Array for Concurrent RF Excitation and Reception Capability for MRI

Radiofrequency (RF) coils based on two operating frequencies, or dual-tuned (DT) coils, for magnetic resonance imaging (MRI) in parallel with MR spectroscopy (MRS) and MR spectroscopy imaging (MRSI) are used to obtain morphological and metabolic information for early diagnosis of diseases. However, this method suffers from serious problems such as the extremely low signal sensitivity of X-nuclei and the long image acquisition time required for the two measurements. In this study, a single-channel DT coil was proposed for RF excitation/reception (Tx/Rx) of hydrogen (1H) and phosphorous (31P) by using a monopole antenna and a loop coil, and it was extended to an eight-channel volume coil at 7 T. To verify the DT coil performance, we compared the single RF port of the DT coil with monopole/loop geometry to the individual coil of the 1H monopole antenna and the 31P loop coil with a cylindrical phantom. The monopole/loop coil shows no magnetic flux interaction between individual coils despite the superimposed positions owing to the single RF port. The study results demonstrated that the proposed DT monopole/loop (DTML) coil can be extended to multiple RF Tx/Rx systems and can reduce the acquisition time with a single measurement.

A Theoretical Study on Circular Wire and Flat Strip Conductor Inductance for Magnetic Resonance-Shielded Phased-Array Circular Coils

Phased-array radiofrequency (RF) coils are commonly used for signal reception in magnetic resonance for their large spatial coverage, typical of volume coils, and for their high signal-to-noise ratio, usually associated with surface coils. The simplest design of phased-array coils is an array of circular loops whose conductor can be constituted by flat strip or circular wire cross-sectional geometry, often partially enclosed in an RF shield for minimizing electromagnetic interference. This paper proposes a method for the analytical calculation of the mutual inductance between two circular loops constituting a dual-element phased-array coil by taking into account the conductor’s geometry and the effect of an eventual RF shield.

Bacterial Nucleoid: Interplay of DNA Demixing and Supercoiling

This work addresses the question of the interplay of DNA demixing and supercoiling in bacterial cells. Demixing of DNA from other globular macromolecules results from the overall repulsion between all components of the system and leads to the formation of the nucleoid, which is the region of the cell that contains the genomic DNA in a rather compact form. Supercoiling describes the coiling of the axis of the DNA double helix to accommodate the torsional stress injected in the molecule by topoisomerases. Supercoiling is able to induce some compaction of the bacterial DNA, although to a lesser extent than demixing. In this work, we investigate the interplay of these two mechanisms with the goal of determining whether the total compaction ratio of the DNA is the mere sum or some more complex function of the compaction ratios due to each mechanism. To this end, we developed a coarse-grained bead-and-spring model and investigated its properties through Brownian dynamics simulations. This work reveals that there actually exist different regimes, depending on the crowder volume ratio and the DNA superhelical density. In particular, a regime in which the effects of DNA demixing and supercoiling on the compaction of the DNA coil simply add up is shown to exist up to moderate values of the superhelical density. In contrast, the mean radius of the DNA coil no longer decreases above this threshold and may even increase again for sufficiently large crowder concentrations. Finally, the model predicts that the DNA coil may depart from the spherical geometry very close to the jamming threshold as a trade-off between the need to minimize both the bending energy of the stiff plectonemes and the volume of the DNA coil to accommodate demixing.