Combination Of Coils Research Articles

A fast and flexible MRI system for the study of dynamic vocal tract shaping.

The aim of this work was to develop and evaluate an MRI-based system for study of dynamic vocal tract shaping during speech production, which provides high spatial and temporal resolution. The proposed system utilizes (a) custom eight-channel upper airway coils that have high sensitivity to upper airway regions of interest, (b) two-dimensional golden angle spiral gradient echo acquisition, (c) on-the-fly view-sharing reconstruction, and (d) off-line temporal finite difference constrained reconstruction. The system also provides simultaneous noise-cancelled and temporally aligned audio. The system is evaluated in 3 healthy volunteers, and 1 tongue cancer patient, with a broad range of speech tasks. We report spatiotemporal resolutions of 2.4 × 2.4 mm2 every 12 ms for single-slice imaging, and 2.4 × 2.4 mm2 every 36 ms for three-slice imaging, which reflects roughly 7-fold acceleration over Nyquist sampling. This system demonstrates improved temporal fidelity in capturing rapid vocal tract shaping for tasks, such as producing consonant clusters in speech, and beat-boxing sounds. Novel acoustic-articulatory analysis was also demonstrated. A synergistic combination of custom coils, spiral acquisitions, and constrained reconstruction enables visualization of rapid speech with high spatiotemporal resolution in multiple planes. Magn Reson Med 77:112-125, 2017. © 2016 Wiley Periodicals, Inc.

Combined use of Onyx and coils for transarterial balloon-assisted embolization of traumatic carotid-cavernous fistulas: a report of 16 cases with 17 fistulas

ObjectiveThe combination of coils and Onyx for the treatment of carotid-cavernous fistulas (CCFs) is an interesting new development. The purpose of the current study is to evaluate our preliminary experience...

Effects of different coil combinations on the optimal design of a 25 T superconducting magnet

High field above 20 T is required in diverse physical programs and nuclear magnetic resonance (NMR) systems. For intended science program requirements, as a demonstration of the development in high field superconducting magnet technology, a 25 T (4.2 K) 52 mm cold-bore all-superconducting magnet consisting of a 10 T high-temperature superconducting insert magnet and a 15 T low-temperature superconducting background magnet, is being developed at the Institute of Electrical Engineering, Chinese Academy of Sciences. The development of such a magnet requires its optimization, and the choosing the number and type of coils is crucial to the final optimal design. However there are few researches focusing on the effect of coil combinations. To study the relationship between the number of coils and the magnet parameters, we first discuss the magnet optimization. The objective function of the optimization is defined as the weighted function of coil volume according to the costs of different superconductors, and the following constraint conditions are taken into considerations: center field, YBCO conductor characterization, hoop stress in Nb3Sn coils, and the critical performances of these wires. All those constraint conditions are taken in the analytical form, and the magnetic field, stress results are verified with the finite element method. To guarantee the reliability of the optimal results, in addition to consider the constraint conditions, a method of combining global optimization and local optimization is adopted. 20 different coil combinations are selected according to the investigation of superconducting wires, and their optimal results are calculated. The following conclusions are drawn from the analyses of these results. Firstly, in the design of high field magnet, the number of coils and magnet cost demonstrate a "V"-shaped relationship, that is, there exist an optimal number of coils. Secondly, when the objective function demonstrates good values, Nb3Sn coils generate fields in a range of 6-7 T, whereas NbTi coils generate fields in a range of 8-9 T. Finally, the objective functions under two different situations, i.e., Nb3Sn coils and NbTi coils are powered together and separately, are calculated. From the comparisons we find that the effect of reducing one power supply is acceptable when the number of coils is not too big.

Ureteral Embolization to Prevent Thrombotic Obstruction of Nephrostomy Catheters in the Context of Refractory Hemorrhagic Radiation Cystitis with Severe Vesicoureteral Reflux.

We present a case of refractory hemorrhagic radiation cystitis in a patient who failed conservative management and was unable to undergo operative urinary diversion secondary to multiple comorbidities. His management was complicated by recurrent obstruction of his nephrostomy catheters due to marked ureteral thrombus formation from blood refluxing into the ureters from the urinary bladder. We were successful in treating his condition by occluding his distal ureters with a combination of embolization coils and glue to prevent the reflux of blood in order to allow his nephrostomy catheters to function properly.

Enhanced phase-sensitive SSFP reconstruction for fat-water separation in phased-array acquisitions.

To propose and assess a method to improve the reliability of phase-sensitive fat-water separation for phased-array balanced steady-state free precession (bSSFP) acquisitions. Phase-sensitive steady-state free precession (PS-SSFP) is an efficient fat-water separation technique that detects the phase difference between neighboring bands in the bSSFP magnetization profile. However, large spatial variations in the sensitivity profiles of phased-array coils can lead to noisy phase estimates away from the coil centers, compromising tissue classification. We first perform region-growing phase correction in individual coil images via unsupervised selection of a fat-voxel seed near the peak of each coil's sensitivity profile. We then use an optimal linear combination of phase-corrected images to segregate fat and water signals. The proposed method was demonstrated on noncontrast-enhanced SSFP angiograms of the thigh, lower leg, and foot acquired at 1.5T using an 8-channel coil. Individual coil PS-SSFP with a common seed selection for all coils, individual coil PS-SSFP with coil-wise seed selection, PS-SSFP after coil combination, and IDEAL reconstructions were also performed. Water images reconstructed via PS-SSFP methods were compared in terms of the level of fat suppression and the similarity to reference IDEAL images (signed-rank test). While tissue misclassification was broadly evident across regular PS-SSFP images, the proposed method achieved significantly higher levels of fat suppression (P < 0.005) and increased similarity to reference IDEAL images (P < 0.005). The proposed method enhances fat-water separation in phased-array acquisitions by producing improved phase estimates across the imaging volume. J. Magn. Reson. Imaging 2016;44:148-157.

Analysis of risk factors for perifocal oedema after endovascular embolization of unruptured intracranial arterial aneurysms.

BackgroundEndovascular embolization is a treatment of choice for the management of unruptured intracranial aneurysms, but sometimes is complicated with perianeurysmal oedema. The aim of our study was to establish incidence and outcomes of perianeurysmal oedema after endovascular coiling of unruptured intracranial aneurysms, and to reveal possible risk factors for development of this potentially serious complication.MethodsIn total 119 adult patients with endovascular embolization of unruptured intracranial aneurysm (performed at Department for Interventional Neuroradiology, Clinical Center, Kragujevac, Serbia) were included in our study. The embolizations were made by electrolite-detachable platinum coils: pure platinum, hydrophilic and combination of platinum and hydrophilic coils. Primary outcome variable was perianeurysmal oedema visualized by magnetic resonance imaging (MRI) 7, 30 and 90 days after the embolization.ResultsThe perianurysmal oedema appeared in 47.6% of patients treated with hydrophilic coils, in 21.6% of patients treated with platinum coils, and in 53.8% of those treated with mixed type of the coils. The multivariate logistic regression showed that variables associated with occurrence of perianeurysmal oedema are volume of the aneurysm, hypertension, diabetes and smoking habit. Hypertension is the most important independent predictor of the perianeurysmal oedema, followed by smoking and diabetes.ConclusionsThe results of our study suggest that older patients with larger unruptured intracranial aneurysms, who suffer from diabetes mellitus and hypertension, and have the smoking habit, are under much higher risk of having perianeurysmal oedema after endovascular coiling.

Selective channel combination of MRI signal phase.

Signal magnitude can robustly be combined using the sum-of-squares approach. Methods have been developed to combine complex images. However, techniques based only on signal phase have not been developed and evaluated. We performed simulations to demonstrate the effect of noise on coil combination. 32-channel 7 Tesla human gradient echo MRI brain data were collected. We combined phase images based on phase noise leading to spatially selective and coil selective combination of phase images. We compared our selective combination approach to optimal noise distribution and adaptive combination methods. We found that selective combination of signal phases leads to improved phase signal-to-noise ratio. Furthermore, a phase shift can be present in combined phase images introduced by the method used to combine multiple channel phases. Mapping of signal phase from ultra-high field MRI data undoubtedly provides a wealth of information about the ageing brain and the effects of neurodegenerative disorders. Measurement of signal phase is essential in frequency shift mapping and in quantitative susceptibility mapping. The method used to combine signal phase should be informed by an understanding of the noise distribution in signal phase at the individual channel level. Magn Reson Med 76:1469-1477, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Armature Design of Low-Voltage FSPMSMs: An Attempt to Enhance the Open-Circuit Fault Tolerance Capabilities

This paper deals with the torque production capabilities of fractional-slot permanent-magnet synchronous machines (FSPMSMs) under open-circuit faulty conditions. The developed approach considers a class of FSPMSMs where an armature is inserted in double-layer slots and is arranged by connecting in parallel the coils or suitable combinations of coils of each phase. In light of this, the machine operates at a low-voltage level. Accordingly, its integration within 42-V-technology-based automotive systems becomes much more realistic. Moreover, the adopted approach leads to a significant improvement in the fault tolerance capability under an open-circuit faulty operation. Indeed, a failure affecting a coil would discard one branch among the parallel branches of the corresponding phase, rather than affecting the total phase in FSPMSMs with series-connected coils in the armature. The approach is initiated by an identification allied to a characterization of the slot/pole combinations enabling the parallel connection of the FSPMSM phase coils or group of coils. Then, this paper considers the selected three-phase and five-phase FSPMSMs. Following an assessment of their healthy operation, the torque values developed by both machines are predicted using a 2-D finite-element analysis under different open-circuit faulty scenarios. Then, a simple control strategy based on the readjustment of the reference sinusoidal current initial phases is proposed to recover the torque production capability of both machines under a branch open-circuit fault.

Correlation between conductivity and prognostic factors in invasive breast cancer using magnetic resonance electric properties tomography (MREPT).

To investigate the correlation between conductivity and prognostic factors of invasive breast cancer using magnetic resonance electric properties tomography (MREPT). This retrospective study was approved by the Institutional Review Board, and verbal informed consent was obtained prior to breast MRI. This study included 65 women with surgically confirmed invasive breast cancers measuring 1cm or larger on T2-weighted fast spin echo (FSE). Phase-based MREPT and the coil combination technique were used to reconstruct conductivity. Simple and multiple linear regression analysis were used to find an independent factor associated with conductivity. In total tumours, tumours with HER-2 overexpression showed lower conductivity than those without, and HER-2 overexpression was independently associated with conductivity. In 37 tumours 2cm or larger, tumours with high mitosis or PR positivity showed higher conductivity than those without, and high mitosis and PR positivity were independently associated with conductivity. In 28 tumours 1-2cm in size, there were no differences in conductivity according to the prognostic factors. Conductivity values measured using MREPT are associated with the HER-2 overexpression status, and may provide information about mitosis and the PR status of invasive breast cancers 2cm or larger. • In all tumours, HER-2 overexpression was independently associated with conductivity. • In tumours ≥ 2cm, high mitosis and PR positivity were associated with conductivity. • Conductivity is associated with the HER-2 overexpression status of invasive breast cancers.

Development of a Conductivity Sensor for Monitoring Groundwater Resources to Optimize Water Management in Smart City Environments.

The main aim of smart cities is to achieve the sustainable use of resources. In order to make the correct use of resources, an accurate monitoring and management is needed. In some places, like underground aquifers, access for monitoring can be difficult, therefore the use of sensors can be a good solution. Groundwater is very important as a water resource. Just in the USA, aquifers represent the water source for 50% of the population. However, aquifers are endangered due to the contamination. One of the most important parameters to monitor in groundwater is the salinity, as high salinity levels indicate groundwater salinization. In this paper, we present a specific sensor for monitoring groundwater salinization. The sensor is able to measure the electric conductivity of water, which is directly related to the water salinization. The sensor, which is composed of two copper coils, measures the magnetic field alterations due to the presence of electric charges in the water. Different salinities of the water generate different alterations. Our sensor has undergone several tests in order to obtain a conductivity sensor with enough accuracy. First, several prototypes are tested and are compared with the purpose of choosing the best combination of coils. After the best prototype was selected, it was calibrated using up to 30 different samples. Our conductivity sensor presents an operational range from 0.585 mS/cm to 73.8 mS/cm, which is wide enough to cover the typical range of water salinities. With this work, we have demonstrated that it is feasible to measure water conductivity using solenoid coils and that this is a low cost application for groundwater monitoring.

Occupancy and Belt Detection in Removable Vehicle Seats Via Inductive Power Transmission

This work proposes the use of inductive links to wirelessly power an autonomous sensor in a vehicle application. The selected application is intended for occupancy and belt detection in removable vehicle seats, where wiring the seat detectors from the vehicle chassis is impractical. The autonomous sensor includes seat detectors and a wireless transceiver to transfer the data on the state of detectors. To compensate the loose coupling between the coupled coils, resonant tanks were used. To drive the transmitting resonant network, a commercial class-D amplifier was used. Working frequency was restricted to 150 kHz. Commercial magnetic-core coils were selected as they provide high coil values and quality factors in a small-size factor, which is a requirement for the intended application. At the receiving network, a rectifier and a voltage regulator were used to provide dc voltage supply to the autonomous sensor. Three kinds of voltage regulators were compared from the point of view of the power efficiency. Both a theoretical analysis and experimental results are presented for different combinations of coils and working frequencies. Theoretical analysis shows that the operating points for the linear shunt regulator always lead to higher power efficiencies compared with other alternatives such as linear series and switching buck regulators. Experimental tests were carried out using a mechanical setup to fix the coil-to-coil distances. Experimental results agree with the theoretical analysis. Achieved power efficiencies ranged from around 50% to 10% for coil-to-coil distances from one to three times the inner diameter of the coils. Experimental tests also showed that the autonomous sensor was properly powered up to coil-to-coil distances of 2.5 cm, i.e., more than four times the inner diameter of the coils.

Experimental and numerical research on process formability in magnetic pulse forming of AZ31 magnesium alloy sheets

The plain strain of AZ31 magnesium alloy sheet in magnetic pulse forming was investigated by numerical simulation and experimental method. Combination of uniform pressure coil and Holmberg’s specimen was employed to evaluate the plain strain of AZ31 sheet. The numerical simulation for magnetic pulse plain strain of AZ31 sheet is performed by means of ANSYS FEA software. The magnetic flux density of uniform pressure coil was distributed uniformly, especially at the center of gauged area of AZ31 sheet directly in relation to the deformation behavior of AZ31 sheet. The velocity of typical point increases as increasing energy, and the more position closes to the center of sheet the higher velocity achieves. The forming height is increased with increasing discharge voltage. Compared with C=768 µF and C=1536 µF, the capacitance of 1152 µF is more effective for forming, which is confirmed by experiments. The peak velocity at the center of sheet is about 105 m/s. The major strains of magnetic pulse plane strain lie approximately in the strain ranges of 5.83-6.45%. However, the 3.22-3.82% (major strain) are the limit strains in quasi-static condition. The experimental results indicate that the major strain of AZ31 sheet improves about 75% compared with the quasi-static case.

Economic Effect of Malaria on Artisanal Fish Production in a Coastal Area of Nigeria

Abstract This study investigated the economic effect of malaria on artisanal fish production in Lagos State, Nigeria. A total of 120 fisher folks households were sampled through a multi-stage random sampling procedure. Primary data which were obtained through administration of structured questionnaire was used for this study. The data were analysed using descriptive statistics, Cost of Illness (COI) approach and ordinary least square (OLS) regression analysis. The study found that 1.67% of the sampled respondent used only mosquito coil as preventive measure while 41.67% of the respondents used a combination of mosquito coil, insecticide and immunization as preventive measures to avert the possible occurrence of malaria among their household members. The mean COI among the fisher folks’ households was ₦109, 995.85 per year, out of which 31.6% was spent on drugs and herbs, 15.5% on hospital consultancy fees while the time cost of illness of both the sick person and the caretaker were 28.4% and 13.1%, respectively. The regression analysis result revealed that aged and experienced fisher folks were more susceptible to malaria attack while number of days absent from work, number of malaria episodes and cost of treatment had adverse effect on fish production in the study area. The study concluded that the incidence of malaria in the households impact negatively on fish catch level. It is therefore recommended, among others, that health care services in the fishing communities be improved while fishers should make proper use of preventive measures so as to reduce cost and number of days lost to illness.

Evaluation of Magnetic-Field Distribution by Screening Current in Multiple REBCO Coils

Coil systems are fabricated with various combinations of multiple coils in order to generate homogenous fields for NMR and MRI applications. In multiple coil systems using REBCO coils, the behavior of the screening current, which deteriorates field homogeneity, depends on the patterns of the transport current, the charging sequence of the coils, and the various resulting magnetic fields. It is therefore important to investigate and clarify the behavior of the irregular magnetic field and screening current in multiple coil systems under different operating environments. In a previous study, we experimentally and numerically clarified the different behaviors of irregular magnetic fields based on the charging sequence of coils in multiple-model REBCO coils [1], [2]. In this paper, we constructed the multiple-model REBCO coils in order to obtain the fundamental data for reducing or improving the resulting irregular magnetic field. Furthermore, the distribution of the irregular magnetic field in terms of the screening current was measured by using the reversal current method [3], [4]. We also calculated the spatial and temporal behavior of the irregular magnetic field by using our developed 3-D numerical simulation. Based on the experimental and numerical results, we discuss the behavior of the magnetic field in terms of the screening current when using the current sweep reversal method in multiple-model REBCO coils.

Direct percutaneous transorbital puncture under fluoroscopic guidance with a 3D skull reconstruction overlay for embolisation of intraorbital and cavernous sinus dural arteriovenous fistulas.

To describe the direct percutaneous transorbital puncture technique for embolisation of the selected intraorbital and cavernous sinus dural arteriovenous fistula, which failed to be treated by conventional endovascular techniques. One case of intraorbital and five cases of cavernous sinus dural arteriovenous fistula were embolised through direct percutaneous transorbital puncture in 2012, and the clinical data were reviewed. Under fluoroscopic guidance with a three-dimensional (3D) skull reconstruction overlay, the cavernous sinus or ophthalmic vein was punctured via the superior orbital fissure. Then a microcatheter was inserted via the needle, and Onyx was injected to embolise the fistula with or without a combination of coils. Complete obliteration of the fistula was achieved in all six patients. After operation all the patients experienced transient swelling of the punctured orbit persisting for three to five days. No other complications occurred. Follow-up of six patients at three to six months showed resolution of their initial neuro-ophthalmological symptoms in five and left visual loss in one did not recover. Six months follow-up angiogram showed no recurrence of these fistulas. Direct percutaneous transorbital puncture provides an option for the intraorbital and cavernous sinus dural arteriovenous fistulas, particularly when the conventional transvenous routes are inaccessible. Overlay of the 3D skull reconstruction can facilitate the precise puncture of the superior orbital fissure.

Pre-operative embolisation of spinal metastasis: technique, complication rate and outcome-clinical experience.

Pre-operative embolisation of metastatic spinal tumours has the potential to decrease intra-operative blood loss. Intra-operative blood loss is multifactorial and one factor may be the embolisation technique used. The purpose of this study was to retrospectively analyse the effect of three different pre-operative embolisation techniques on intra-operative blood loss, complication rate and tumour aetiology in patients treated with a corpectomy and dorsoventral stabilisation at our institution. We conducted a retrospective analysis of embolisation procedures for vertebral metastases performed from January 2002 to December 2011. Only pre-operatively embolised patients treated by a single-level hemicorpectomy or corpectomy procedure from T4-L5, including posterior spinal stabilisation using pedicle screws, were included. All patient charts and examinations were analysed regarding the embolisation technique, gender, age, primary tumour, time between the embolisation and surgery, intra-operative blood loss, intra-operative transfusions and complications related to embolisation. We identified a total of 46 patients, 25 male and 21 female patients. The mean age at the time of surgery was 66 years (range 39-84 years). The tumours treated were: 15 (33%) renal cell carcinomas, six (13%) breast carcinomas, five (11%) lung carcinomas, five (11%) urothelial carcinomas, four (9%) myelomas and 11 (24%) miscellaneous types including rectal carcinoma, thymoma and melanoma. Embolisation with coils was performed in 23 patients, particles were used in six and a combination of coils and particles in 18. The mean time between the embolisation and surgery was 23 hours (range 80-4,430 minutes). The median overall intra-operative estimated blood loss (EBL) was 2,300 ml (range 500-15,000 ml). In patients embolised with coils and particles, EBL was 2,200 ml compared to 1,450 ml in patients embolised with particles and 2,500 ml in the coil group. No statistically significant differences between the three groups could be detected. There were no complications related to the embolisation techniques. Pre-operative embolisation of spinal metastases using coils, particles or a combination of both is a safe and reproducible procedure. In our cohort we reported no complications during the three different embolisation techniques. No statistically significant difference regarding blood loss between the three embolisation techniques could be detected. Our data confirm existing studies concerning the control of intra-operative blood loss using different embolisation techniques. The benefit of embolisation with a combination of coils and particles compared to embolisation with particles only is questionable.

Tumor necrosis after preventive embolization of large renal angiomyolipomas.

The purpose of this study was to retrospectively evaluate tumor necrosis following preventive embolization in patients with renal angiomyolipoma (RAML) at high risk of bleeding. Arterial embolization was performed in 24 patients (22 women, 2 men; mean age, 43±13 years) with a total of 30 RAMLs (mean volume, 137 cm(3)±163) between 1996 and 2012. Two sub-groups of patients were identified and further compared based on the presence or not of necrosis following arterial embolization. The technical and clinical success rates of arterial embolization of RAMLs were 97% and 87%, respectively. The mean initial volume of RAMLs differed between the two sub-groups with 331cm(3) in the group with tumor necrosis and 88 cm(3) in the group without tumor necrosis (P=0.0047). High-fat content RAMLs were predominantly observed in the necrosis group and the mean volume reduction observed for high-fat RAMLs was 65% whereas it was 36% for low-fat content RAMLs. The six patients who developed RAML necrosis had arterial embolization using microspheres (one patient with microspheres alone and five with a combination of microspheres and metallic coils). All necrotic RAMLs displayed arterial dysplasia. The risk of tumor necrosis is higher for larger RAMLs. The role of distal arterial embolization with microspheres in tumor necrosis in RAML is suggested by the results of our study but could not be definitely demonstrated statistically due to the limited sample size.

Coil combination for receive array spectroscopy: Are data-driven methods superior to methods using computed field maps?

PurposeCombining spectra from receive arrays, particularly X‐nuclear spectra with low signal‐to‐noise ratios (SNRs), is challenging. We test whether data‐driven combination methods are better than using computed coil sensitivities.TheorySeveral combination algorithms are recast into the notation of Roemer's classic formula, showing that they differ primarily in their estimation of coil receive sensitivities. This viewpoint reveals two extensions of the whitened singular‐value decomposition (WSVD) algorithm, using temporal or temporal + spatial apodization to improve the coil sensitivities, and thus the combined spectral SNR.MethodsRadiofrequency fields from an array were simulated and used to make synthetic spectra. These were combined with 10 algorithms. The combined spectra were then assessed in terms of their SNR. Validation used phantoms and cardiac 31P spectra from five subjects at 3T.ResultsCombined spectral SNRs from simulations, phantoms, and humans showed the same trends. In phantoms, the combined SNR using computed coil sensitivities was lower than with WSVD combination whenever the WSVD SNR was >14 (or >11 with temporal apodization, or >9 with temporal + spatial apodization). These new apodized WSVD methods gave higher SNRs than other data‐driven methods.ConclusionIn the human torso, at frequencies ≥49 MHz, data‐driven combination is preferable to using computed coil sensitivities. Magn Reson, 2015. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Magn Reson Med 75:473–487, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

A subspace-based coil combination method for phased-array magnetic resonance imaging.

Coil-by-coil reconstruction methods are followed by coil combination to obtain a single image representing a spin density map. Typical coil combination methods, such as square-root sum-of-squares and adaptive coil combining, yield images that exhibit spatially varying modulation of image intensity. Existing practice is to first combine coils according to a signal-to-noise criterion, then postprocess to correct intensity inhomogeneity. If inhomogeneity is severe, however, intensity correction methods can yield poor results. The purpose of this article is to present an alternative optimality criterion for coil combination; the resulting procedure yields reduced intensity inhomogeneity while preserving contrast. A minimum mean squared error criterion is adopted for combining coils via a subspace decomposition. Techniques are compared using both simulated and in vivo data. Experimental results for simulated and in vivo data demonstrate lower bias, higher signal-to-noise ratio (about 7×) and contrast-to-noise ratio (about 2×), compared to existing coil combination techniques. The proposed coil combination method is noniterative and does not require estimation of coil sensitivity maps or image mask; the method is particularly suited to cases where intensity inhomogeneity is too severe for existing approaches.

Three-layered radio frequency coil arrangement for sodium MRI of the human brain at 9.4 Tesla.

A multinuclei imaging setup with the capability to acquire both sodium ((23) Na) and proton ((1) H) signals at 9.4 Tesla is presented. The main objective was to optimize coil performance at the (23) Na frequency while still having the ability to acquire satisfactory (1) H images. The setup consisted of a combination of three radio frequency (RF) coils arranged in three layers: the innermost layer was a 27-channel (23) Na receive helmet which was surrounded by a four-channel (23) Na transceiver array. The outer layer consisted of a four-channel (1) H dipole array for B0 shimming and anatomical localization. Transmit and receive performance of the (23) Na arrays was compared to a single-tuned (23) Na birdcage resonator. While the transmit efficiency of the (23) Na transceiver array was comparable to the birdcage, the (23) Na receive array provided substantial signal-to-noise ratio (SNR) gain near the surface and comparable SNR in the center. The utility of this customized setup was demonstrated by (23) Na images of excellent quality. High SNR, efficient transmit excitation and B0 shimming capability can be achieved for (23) Na MRI at 9.4T using novel coil combination. This RF configuration is easily adaptable to other multinuclei applications at ultra high field (≥ 7T).