Hemispherical gradient coils for magnetic resonance imaging

Green, Dan; Leggett, James; Bowtell, Richard

doi:10.1002/mrm.20603

Cited by 23 publications

(19 citation statements)

References 17 publications

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“…Liu and Petropoulos (71) described the design of spherical z-gradient coil using minimum inductance approach. Green et al (72) took the hemispherical gradient coil idea and adds a term where consider the total torque formed from a stream function (77). When this is not considered, the net torque makes its operation at high currents and fields problematic, although this inclusion of torque-balancing produces a considerable reduction of the performance of the transverse hemispherical coils, as is also the case for asymmetric, cylindrical coils.…”

Section: Torquementioning

confidence: 99%

Theory of gradient coil design methods for magnetic resonance imaging

Hidalgo-Tobón

2010

Concepts Magnetic Resonance

133

104

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The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. In simple terms, an magnetic resonance imaging (MRI) system consists of five major components: a magnet, gradient systems, an RF coil system, a receiver, and a computer system. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. In modern MRI, gradient coils able to generate high gradient strengths and slew rates are required to produce high imaging speeds and improved image quality. MRI also requires the use of gradient coils that generate magnetic fields, which vary linearly with position over the imaging volume. Gradient coils for MRI must therefore have high current efficiency (defined as the ratio of gradient generated to current drawn), short switching time (i.e., low inductance), gradient linearity over a large volume, low power consumption, and minimal interaction with any other equipment, which would otherwise result in eddy currents. Over the last two decades new methods of gradient coil design have been developed, and a combination of these methods can be a mixture of them trying to avoid discomforts to patients that at the end is the center of all the technological efforts in the art of MRI.

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Section: Torquementioning

confidence: 99%

Theory of gradient coil design methods for magnetic resonance imaging

Hidalgo-Tobón

2010

Concepts Magnetic Resonance

133

104

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“…Myers and Roemer showed that cylindrical gradient coils with asymmetrically positioned regions of uniformity (ROU) have high efficiency and reasonable gradient field uniformity (8). There are many more examples of coil designs that deviate from cylindrical geometry; planar gradients for NMR microscopy (9) and ''open'' MRI systems (10), gradients with a hemispherical geometry for brain imaging (11,12), gradients with parabolic return paths to accommodate the shoulders (13), conical section surfaces linking the primary to the shield for short gradients (14), gradients with multiple regions of interest (ROI) (15) and MAMBA coils for simultaneous acquisition of images from different sample regions (16).…”

Section: Introductionmentioning

confidence: 99%

Novel gradient coils designed using a boundary element method

Poole

Bowtell

2007

Concepts Magn Reson

Self Cite

160

156

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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-B 0 arrays (MAMBA); iv) an insertable set of head gradient coils with shoulder cutouts.

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“…Another design method (11) represents current density on the primary coil by a finite series expansion, assuming the shield coil is much longer than the primary coil. Though most methods are typically used to design whole-body gradients, they have also been applied to small animal imaging and organ-specific imaging applications such as kidney and head (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29).…”

Section: Introductionmentioning

confidence: 99%

“…Designing a small-head gradient coil, in particular, requires advanced optimization techniques because of gradient performance tradeoffs forced by the need to take body shape, primarily the shoulders, into account. Various methods have been proposed: parabolic shoulder cutouts (20,21), gradients with an asymmetric center position (18-20, 23, 24, 27), a symmetric gradient (26,28), an edge gradient (26), and a hemispherical gradient (29). There have also been other head gradient design developments, such as the use of axial return paths (25,28).…”

Section: Introductionmentioning

confidence: 99%

Discrete design method of transverse gradient coils for MRI

Shvàrtsman¹,

Steckner²

2007

Concepts Magn Reson

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A method is presented for designing transverse gradient coils for magnetic resonance imaging. This method is based on the set of Z intercepts of the coils' current patterns with the z axis in the unfolded z-arc plane. We show that the set of Z intercepts combined with a description of the coil topology, as defined by the necessary azimuthal harmonics, the axial symmetry and the directions of the current flow, is sufficient for designing a practical gradient coil. The theory and design of transverse coils with Z intercepts is illustrated with examples of a symmetric unshielded insert gradient coil for small animal imaging, a human head unshielded symmetric insert gradient coil with shoulder cutouts, and a self-shielded short whole-body gradient coil. The Z-intercept method has also been extended to design higher-order transverse shims. This is illustrated with the design of a ZX shim. Additional design capabilities of the Z-intercepts method are also discussed.

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Hemispherical gradient coils for magnetic resonance imaging

Cited by 23 publications

References 17 publications

Theory of gradient coil design methods for magnetic resonance imaging

Theory of gradient coil design methods for magnetic resonance imaging

Novel gradient coils designed using a boundary element method

Discrete design method of transverse gradient coils for MRI

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