Sensitive-volume localization for in vivo NMR using heteronuclear spin-echo pulse sequences.

31P/ 1H WALTZ-4 broadband decoupling at 1.5 T: different versions of the composite pulse and consequences when using a surface coil

We present a scalable uniform technique for construction of highly conditional C$^n$-NOT quantum gates of trapped ion qubits, such as the Toffoli gate, without using ancilla states and circuits of an exorbitant number of concatenated one- and two-qubit gates. Apart from the initial dressing of the internal qubit states with vibrational phonons and the final restoration of the phonon ground state, our technique requires the application of just a single composite pulse on the target qubit and is applicable both in and outside the Lamb-Dicke regime. We design special narrowband composite pulses, which suppress all transitions but the conditional transition of the target qubit; moreover, these composite pulses significantly improve the spatial addressing selectivity.

In order to improve the performance of magnetic resonance imaging and spectroscopy of atherosclerotic plaque the potential use of novel radiofrequency coil structures with sensitive detection volumes tailored to the geometry of the arterial wall was investigated. It was found that a cylindrical meanderline (zig-zag) coil design provides a sensitive volume that is restricted to a cylindrical shell, thereby maximizing the filling factor and signal-to-noise ratio for plaques while reducing the intense blood signal. The cylindrical meanderline coil has the added advantages of an open interior, which allows for unimpeded blood flow during scanning, and the potential to be expanded against the walls of the artery, thereby stabilizing the coil against the pulsatile blood flow and minimizing motion artifacts. The performance of cylindrical meanderline coils with theoretical simulations of the electromagnetic fields as well as with experimental images of test objects (phantoms) and human endarterectomy surgical specimens is demonstrated. This radically new RF coil geometry offers the potential to improve the efficiency of MR data acquisition in medical applications in which curved surfaces or slabs contain the material of interest.

RF coils play an important role to acquire MR images with the maintenance of high homogeneity in high field MR system more than 3.0 T. Many kinds of RF coils such as birdcage coil, STR, surface coil, and phase array coil have been used, however, the good uniformity of a coil has always been an issue. In this paper, comparison of B(1) homogeneity between birdcage and phase array coil was investigated using FDTD method at 3.0 T MRI in order to develop RF coils with the high uniformity. Three different configurations of the FDTD simulation were performed like as using a free space configuration, water phantom configuration, and head mesh model. B1 homogeneity was calculated to the case of birdcage coil and 8-channel phase array coil in each configuration of simulation. Improvement on the homogeneity of the images and reduction of standing wave effect was achieved with comparing the real MR images with the result from simulation.

This study is an evaluation of the ratio of electric field to magnetic field (E/B1), specific absorption rate (SAR) and signal-to-noise ratio (SNR) generated by three different RF transceiver coil setups: surface coil, surface coil with shielding, and microstrip using a finite discrete time domain (FDTD) simulation in the presence of a head phantom. One of our main focuses in this study is to better understand coil designs that would improve patient safety at high fields by studying a coil type that may potentially minimize SAR while examining potential changes in SNR. In the presence of a human head load, the microstrip's E/B1 ratio was on average smallest while its SAR was also on average smallest of the three setups, suggesting the microstrip may be a better RF coil choice for MRI concerning patient safety and parallel excitation applications than the other two coils. In addition, the study suggests that the microstrip also has a higher SNR compared with the other two coils demonstrating the possibility that the microstrip could lead to higher quality MRI images.

IntroductionThe purpose of this study was to demonstrate the feasibility and efficiency of cardiac MR at 3 Tesla using local four-channel RF coil transmission and benchmark it against large volume body RF coil excitation.MethodsElectromagnetic field simulations are conducted to detail RF power deposition, transmission field uniformity and efficiency for local and body RF coil transmission. For both excitation regimes transmission field maps are acquired in a human torso phantom. For each transmission regime flip angle distributions and blood-myocardium contrast are examined in a volunteer study of 12 subjects. The feasibility of the local transceiver RF coil array for cardiac chamber quantification at 3 Tesla is demonstrated.ResultsOur simulations and experiments demonstrate that cardiac MR at 3 Tesla using four-channel surface RF coil transmission is competitive versus current clinical CMR practice of large volume body RF coil transmission. The efficiency advantage of the 4TX/4RX setup facilitates shorter repetition times governed by local SAR limits versus body RF coil transmission at whole-body SAR limit. No statistically significant difference was found for cardiac chamber quantification derived with body RF coil versus four-channel surface RF coil transmission. Our simulation also show that the body RF coil exceeds local SAR limits by a factor of ~2 when driven at maximum applicable input power to reach the whole-body SAR limit.ConclusionPursuing local surface RF coil arrays for transmission in cardiac MR is a conceptually appealing alternative to body RF coil transmission, especially for patients with implants.

Purpose: The purpose of this study was to enhance the technical improvement which can develop the advanced sensitive RF surface coil to investigate the sensitivities of the multi‐spiral surface coils and eventually achieve the high resolution of microscopic MR images and MR spectra. Method and Materials: The simulation of a coil's magnetic field was processed in MATLAB. Biot‐Savart law provides information about the relation between the amplitude and the position. The experiment was processed in the Oxford magnet (1.5T), Copley gradient (25mT/m) coil and Analogic RF amplitude system. The diameter of a coil was fixed at 4cm, and the turn of a coil was increased with a spiral turning method. Results: 1. Simulation of magnetic field. The magnetic field strength was increased close to the wire because of a ring‐shape wire coil. This simulation was performed assuming no obstruction in the current and domain. Thus, the shape and the field distribution of a RF surface coil were able to be visually analyzed. 2. Coils' performance. The ROI with approximately 3cm was identified by a water phantom in 1.5T. The three and five turned spiral coils were developed and their Q‐factor and bandwidth were estimated. Conclusion: The present study showed that the sensitivity of RF surface coil was improved by the increasing the number of a spiral coil's turn, and also the SNR of RF surface coil was dependent upon the number of a spiral coil's turn. However, the sensitivity was not proportional to the number of a spiral RF coil's turn. There is an optimal vale in a spiral RF coil turn and sensitivity. In order to obtain a high sensitivity as varying the spiral RF coil's performance, it is important to find the optimal number of turn. This study provides an efficient approach to designing high‐field RF coils.

Spin evolution in a radio frequency field studied through muon spin resonance

A neutral current single sensor sampling composite zero vector pulse width modulation (CZV-PWM) phase current reconstruction strategy for three-level inverter is proposed in this paper. Firstly, the sampling principle of T-type three-level inverter with neutral current sensor is analyzed and the existence mechanism of unobservable region of the neutral current is investigated. Then, by compensating the observable voltage vector that does not meet the minimum sampling time requirement in different regions, and providing sampling windows by three end-to-end vectors, the CZV principle is proposed. Finally, experiments were performed and the results show that the current reconstruction error of the proposed method is lower than 2.5%, and the phase current THD is lower than 3.21%, which can provide accurate reconstructed phase current for the control system.

A method of determining arterial input function (AIF) by continuously detecting the (17)O MR signal changes of (17)O-labeled water tracer in the rat carotid artery using a region-defined (REDE) implanted vascular RF coil at 9.4 Tesla is reported. This coil has a compact physical size of 1 mm inner diameter, 3 mm outer diameter and 11 mm in length. It can be readily implanted into the rat neck and wrapped around the rat carotid artery for achieving adequate MR detection sensitivity for determining AIF with minimal surgical trauma. Water phantom and in vivo MR experiments were conducted for validating the coil's performance. A signal-to-noise ratio of approximately 20:1 was achieved for the (17)O signal acquired from naturally abundant H(2)(17)O in a small amount of blood (approximately 7 microl) inside the rat carotid artery with an acquisition time of 11 s. The REDE RF coil design electromagnetically isolates the rat carotid artery from surrounding tissues and ensures that the MR signal detected by the RF coil is only attributable to the artery blood. It also minimizes the electromagnetic coupling between the implanted RF coil and a head surface coil tuned at the same operating frequency (two-coil configuration). This configuration allowed simultaneous measurements of dynamic changes of (17)O MR signal of the H(2)(17)O tracer in both rat carotid artery and brain. Compared to most contemporary MR approaches, the REDE implanted RF provides a simple, accurate, and promising solution for determination of AIF in small experimental animals.

Phase-modulated rotating-frame spectroscopic localization using an adiabatic plane-rotation pulse and a single surface coil

PurposeThis study aims (1) to implement a robust acquisition, fully automated reconstruction, and processing pipeline using a novel rosette k‐space pattern for UTE 31P 3D MRSI and (2) to evaluate the clinical applicability and reproducibility at different experimental setups.MethodsA multi‐center feasibility/reproducibility study was conducted for the novel UTE 31P 3D MRSI sequence with rosette petal trajectory (PETALUTE) at three institutions with different experimental setups (Siemens Prisma with volume head coil or surface coil, Siemens Biograph mMR with volume head coil). Five healthy subjects at each site were measured with an acquisition delay of 65 μs and a final resolution of 10 × 10 × 10 mm3 in 9 min. The measurement was repeated three times and averaged for the spectral analysis using the LCModel package. The potential for acceleration was assessed using compressed sensing on retrospectively undersampled data. Reproducibility at each site was evaluated using the inter‐subject coefficient of variance.ResultsThis novel acquisition and advanced processing techniques yielded high‐quality spectra and enabled the detection of the critical brain metabolites at three different sites with different hardware specifications. In vivo, feasibility with an acceleration factor of 4 in 6.75 min resulted in a mean Cramér‐Rao lower bounds below 20% for phosphocreatine (PCr), adenosine triphosphate (ATP), phosphomonoesters (PME), and a mean coefficient of variation for ATP/PCr below 20%.ConclusionWe demonstrated that UTE 31P 3D rosette MRSI acquisition, combined with compressed sensing and LCModel analysis, allows clinically feasible, robust, high‐resolution 31P MRSI to be acquired at clinical setups.

Special designed RF-antenna with integrated non-invasive carbon electrodes for simultaneous magnetic resonance imaging and electroencephalography acquisition at 7T

Phosphorus (31P) MRS, combined with saturation transfer (ST), provides non‐invasive insight into muscle energy metabolism. However, even at 7 T, the standard ST method with T1app measured by inversion recovery takes about 10 min, making it impractical for dynamic examinations. An alternative method, i.e. four‐angle saturation transfer (FAST), can shorten the examination time. The aim of this study was to test the feasibility, repeatability, and possible time resolution of the localized FAST technique measurement on an ultra‐high‐field MR system, to accelerate the measurement of both Pi‐to‐ATP and PCr‐to‐ATP reaction rates in the human gastrocnemius muscle and to test the feasibility of using the FAST method for dynamic measurements.We measured the exchange rates and metabolic fluxes in the gastrocnemius muscle of eight healthy subjects at 7 T with the depth‐resolved surface coil MRS (DRESS)‐localized FAST method. For comparison, a standard ST localized method was also used. The measurement time for the localized FAST experiment was 3.5 min compared with the 10 min for the standard localized ST experiment. In addition, in five healthy volunteers, Pi‐to‐ATP and PCr‐to‐ATP metabolic fluxes were measured in the gastrocnemius muscle at rest and during plantar flexion by the DRESS‐localized FAST method.The repeatability of PCr‐to‐ATP and Pi‐to‐ATP exchange rate constants, determined by the slab‐selective localized FAST method at 7 T, is high, as the coefficients of variation remained below 20%, and the results of the exchange rates measured with the FAST method are comparable to those measured with standard ST.During physical activity, the PCr‐to‐ATP metabolic flux decreased (from FCK = 8.21 ± 1.15 mM s−1 to FCK = 3.86 ± 1.38 mM s−1) and the Pi‐to‐ATP flux increased (from FATP = 0.43 ± 0.14 mM s−1 to FATP = 0.74 ± 0.13 mM s−1).In conclusion, we could demonstrate that measurements in the gastrocnemius muscle are feasible at rest and are short enough to be used during exercise with the DRESS‐localized FAST method at 7 T. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

The influence of partial tumor sampling in a volume of interest (VOI) on the ratios of phosphorus metabolites was examined by localized phosphorus magnetic resonance spectroscopy (P-31-MRS). Experiments were performed to investigate the characteristics of the surface coil used and precession of spatial localization. A total of 24 patients with liver metastases and 20 volunteers were studied by P-31-MRS. Patients were divided in two groups: VOI < 50% (n = 8) and VOI > 50% (n = 16) occupied by tumor. For evaluation of the surface coil and localization method (image selected in vivo spectroscopy), phantom studies were performed. Superficial focal liver tumors were detectable with a surface coil at a distance within the coil radius. The image selected in vivo spectroscopy permitted the study of phosphorus metabolism in a defined VOI, phosphomonoester/beta-adenosine triphosphate and phosphodiester/beta-adenosine triphosphate were elevated significantly in spectra of both patient groups. Detection of small tumor volumes within a VOI filled by less than 50% of the tumor is possible, with results statistically different from that in normal volunteers.