Concepts in Magnetic Resonance Part B-magnetic Resonance Engineering 

About: Concepts in Magnetic Resonance Part B-magnetic Resonance Engineering is an academic journal published by Wiley-Blackwell. The journal publishes majorly in the area(s): Electromagnetic coil & Radiofrequency coil. It has an ISSN identifier of 1552-5031. It is also open access. Over the lifetime, 335 publications have been published receiving 5895 citations. The journal is also known as: Magnetic resonance engineering.

Application of a Fourier‐based method for rapid calculation of field inhomogeneity due to spatial variation of magnetic susceptibility

Abstract: Inhomogeneous B0-magnetic fields generate distortion in magnetic resonance images, particularly those produced using echo planar imaging, and are responsible for signal reduction due to intravoxel dephasing in gradient echo experiments. Such effects increase in magnitude in proportionality with the static field strength, and with the growing use of high-field (3 T and above) systems in medical imaging, it is increasingly important to be able to quantify field inhomogeneities. Here, we describe the implementation and use of a method for rapidly calculating frequency shifts due to spatially varying magnetic susceptibility that is based on an approach previously used to calculate long-range dipolar field effects. The method relies on a simple expression that relates the three-dimensional Fourier transforms of the magnetization distribution and the field, and can naturally include the effect of the sphere of Lorentz. It has been used to evaluate field inhomogeneity in the head due to the variation of magnetic susceptibility with tissue type and to calculate the change in field inhomogeneity that occurs due to small rotations of the head. In addition, this approach has been used to simulate the effect of lung volume changes in generating respiration induced resonant offsets in the brain. © Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 25B: 65–78, 2005

A fast calculation method for magnetic field inhomogeneity due to an arbitrary distribution of bulk susceptibility

Abstract: A fast calculation method for the magnetic field distribution due to (dynamic) changes in susceptibility may allow real-time interventional applications. Here it is shown that a direct relationship can be obtained between the magnetic field perturbation and the susceptibility distribution inside the MR magnet using a first order perturbation approach to Maxwell's magneto-static equations, combined with the Fourier transformation technique to solve partial derivative equations. The mathematical formalism does not involve any limitation with respect to shape or homogeneity of the susceptibility field. A first order approximation is sufficient if the susceptibility range does not exceed 10−4 (or 100 ppm). The formalism allows fast numerical calculations using 3D matrices. A few seconds computation time on a PC is sufficient for a 128 × 128 × 128 matrix size. Predicted phase maps fitted both analytical and experimental data within 1% precision. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 19B: 26–34, 2003.

Design and construction of a dipolar Halbach array with a homogeneous field from identical bar magnets: NMR Mandhalas

Abstract: Magnets of the Halbach layout are interesting for the use in mobile NMR/MRI devices. Therefore, the ideal Halbach magnet was iterated using identical bar magnets, which are positioned and oriented based on analytical equations. These configurations were simulated with two-dimensional finite-element methods. Performance factors were defined to relate field strength with homogeneity and mass. A geometry of 16 magnets provided a good compromise between performance and special requirements for the desired use to store hyperpolarized xenon. The construction of such a magnet required the design of dedicated support frames and procedures to mount them. The field strength and homogeneity in the finished magnet were measured by a Hall probe and agreed well with the simulations. The calculation and construction are described in detail and together with the tabled field values for n magnets with n ≤ 80 may prove helpful for building similar devices, which were named NMR Mandhalas (Magnet Arrangements for Novel Discrete Halbach Layout). © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 23B: 16–25, 2004

Design and performance of a DNP prepolarizer coupled to a rodent MRI scanner

Abstract: For most of the last forty years, the techniques of Dynamic Nuclear Polarization (DNP) have been confined to particle-physics laboratories building polarized targets, but recently it has been shown that samples similar to a solid target can be transformed into room temperature liquid solutions while retaining a high nuclear polarization. This method of "hyperpolarization" is of interest in NMR/MRI/MRS. We describe a 3.35 T DNP/9.4 T MRI installation based on a continuous-flow cryostat, using a standard wide-bore low-field NMR magnet as prepolarizer magnet and a widely available radical as polarizing agent. The interfacing to a rodent scanner requires that the infusion of the polarized solution in the animal be remotely controlled, because of limited access inside the magnet bore. Physiological constraints on the infusion rate can be a serious source of polarization loss, and the discussion of efficiency is therefore limited to that of the prepolarizer itself, i.e., the spin temperatures obtained in the solid state. To put our results in context, we summarize data obtained in targets with different types of radicals, and provide a short review of the DNP mechanisms needed in their discussion. (C) 2007 Wiley Periodicals, Inc.

Novel gradient coils designed using a boundary element method

Abstract: Boundary element methods offer a powerful approach for designing gradient coils, allowing the generation of coils wounds on arbitrarily shaped surface so as to produce any form of field variation that is consistent with Maxwell's equations. These methods are based on meshing the current carrying surface into an array of boundary elements. In this work, we have extended boundary element methods that have previously been used used for coil design and integrated a powerful mesh generating program so as to produce coils with totally arbitrary geometry. Four examples are used to illustrate how the modified method provides a single versatile coil design protocol. These relate to the design of: i) shielded head gradients with highly asymmetric surface geometry that give the highest possible gradient field strengths; ii) very short, shielded gradient coils to allow improved access to the subject; iii) bi-planar coils generating highly asymmetric, stepped magnetic fields for use in fast imaging by multiple acquisition with micro-B0 arrays (MAMBA); iv) an insertable set of head gradient coils with shoulder cut-outs