Theory of gradient coil design methods for magnetic resonance imaging

Abstract

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.

A theoretical study for the inverse design of an ellipsoidal phased-array breast coil

“…Therefore, the y-component of the magnetic field (H y ) (in local coordinates) that is considered in the work is equivalent to the H X in the system coordinates. The expressions for the y-component of the induced magnetic field vector at any field point (x, y, z) in Cartesian coordinates are expressed as (5) where,   sinh ( ); sinh ( ); cosh( ); cosh( );…”

“…The inverse design methods have been reviewed firstly by Turner [4], and recently by Hidalgo-Tobon [5] for gradient coils design. This method was later employed by Fujita et al for the design of the RF coils.…”

Qualitative analysis of Fruits and Vegetables using Earth’s Field Nuclear Magnetic Resonance (EFNMR) and Magnetic Resonance Imaging (MRI)

“…There are various imaging techniques in biomedical field such as ultrasonic [1][2][3][4][5], X-rays [6][7][8][9][10][11] and NMR [12][13][14][15][16][17][18][19][20][21]. Among the imaging techniques, magnetic resonance imaging (MRI) is effective, powerful and reliable.…”

Goodbye wires and formers: 3-D additive manufacturing and fractal cooling applied to construction of MRI gradient coils

“…Most importantly, conductivities were attained that were close to bulk conductivity. As in other application of computer controlled numerical machining, we expect that our approach would be a good match to the simulations typically employed to optimize the design of gradient coils[4,7,21,22]. Frankly, we cannot imagine any other way to implement the fractal cooling schemes [19] that promise to significantly improve duty cycles at the high power typically required by MRI gradient systems.…”