Abstract:A light weight, simple design NMR apparatus consists of 24 identical magnets arranged in Halbach array was designed and built. The homogeneity of the magnetic field B0 can be improved by dividing a long magnets into several rings. The size of the useful volume depends on both the gap between each ring and some others shim magnets. Our aim is to enhance the sensitive volume and to maintain the highest magnetic static field (B0). This apparatus generates a B0 field strength of about 0.1 T. This work focuses on t… Show more
“…a volume of 3 x 3 x 5 mm 2 in [36] and 5 x 5 x 5 mm 3 for a homogeneity of less than 0.1 mT/0.311 T and 18 x 18 x 30 mm 3 with a homogeneity of 700 ppm in [43]. Shimming methods such as adding small magnetic shimming blocks inside the cylinder were proposed [44,45].…”
Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable "point-of-care" and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on nonlinear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable lowcost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.
“…a volume of 3 x 3 x 5 mm 2 in [36] and 5 x 5 x 5 mm 3 for a homogeneity of less than 0.1 mT/0.311 T and 18 x 18 x 30 mm 3 with a homogeneity of 700 ppm in [43]. Shimming methods such as adding small magnetic shimming blocks inside the cylinder were proposed [44,45].…”
Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable "point-of-care" and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on nonlinear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable lowcost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.
“…Two different designs are produced in [12]. At first, Halbach magnet is combined from two main rings with a gap between them (this gap is optimized) and two shim rings is installed inside the main rings.…”
Nowadays, Halbach magnets serve different purposes in electrical machine designs by offering different structures. These structures can be used to shim (improve the inhomogeneity) of new static fields in the magnetic resonance imaging (MRI) system. The shimming method proposed here uses axial and radial Halbach arrays. The inhomogeneity and average field is obtained at a constant diameter of spherical volume. Using the Maxwell software, different topologies are evaluated and the best structure is then selected and optimized. The optimum structure is manufactured and all issues related to the construction are explained in details. Comparison between simulation and experimental results shows the effectiveness of the proposed idea.
At present, the application of magnetizers (magnetic conditioners) is increasingly booming, in the different branches of socioeconomic work such as Industry, Agriculture, and Medicine. In this work the calculation and design of a magnetizer is proposed; formed by equal permanent magnets type Halbach with rectangular shape, distributed and confined in a non-ferromagnetic structure, circular section in the form of a ring, consisting of an octagonal inner circle, with a magnetic field induction (25,7-42,8) mT and a homogeneity of magnetic field, in the volume of interest, of 1,5 x 10-2 ppm (in a sphere of radius of 0,025 m), in the center of the configuration lines are distributed transversally for different water flow capacities.
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