Validation of numerical methods for electromagnetic dosimetry through near-field measurements

This paper describes the arrangement of a first experimental set-up which allows the comparison between the measurement of the electromagnetic field quantities induced inside a simple cylindrical phantom and the same quantities estimated numerically through a boundary element method. The reliability of the numerical method has been tested at 64 MHz, the Larmor frequency associated to the magnetic resonance imaging devices with an isocenter magnetic field of 1.5 T. To assess its robustness, the comparison is also performed by introducing, inside the phantom, a metallic non magnetic element, which roughly simulates a medical implant.

Download Full-text

B0-Shimming Methodology for Affordable and Compact Low-Field Magnetic Resonance Imaging Magnets

Frontiers in Physics ◽

10.3389/fphy.2021.704566 ◽

2021 ◽

Vol 9 ◽

Author(s):

Konstantin Wenzel ◽

Hazem Alhamwey ◽

Tom O’Reilly ◽

Layla Tabea Riemann ◽

Berk Silemek ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Magnetic Resonance ◽

Point Of Care ◽

Low Cost ◽

Field Measurements ◽

Target Volume ◽

Resonance Imaging ◽

Low Field ◽

Magnetic Resonance Imaging Mri

Low-field (B0 < 0.2 T) magnetic resonance imaging (MRI) is emerging as a low cost, point-of-care alternative to provide access to diagnostic imaging technology even in resource scarce environments. MRI magnets can be constructed based on permanent neodymium-iron-boron (NdFeB) magnets in discretized arrangements, leading to substantially lower mass and costs. A challenge with these designs is, however, a good B0 field homogeneity, which is needed to produce high quality images free of distortions. In this work, we describe an iterative approach to build a low-field MR magnet based on a B0-shimming methodology using genetic algorithms. The methodology is tested by constructing a small bore (inner bore diameter = 130 mm) desktop MR magnet (<15 kg) at a field strength of B0 = 0.1 T and a target volume of 4 cm in diameter. The configuration consists of a base magnet and shim inserts, which can be placed iteratively without modifying the base magnet assembly and without changing the inner dimensions of the bore or the outer dimensions of the MR magnet. Applying the shims, B0 field inhomogeneity could be reduced by a factor 8 from 5,448 to 682 ppm in the target central slice of the magnet. Further improvements of these results can be achieved in a second or third iteration, using more sensitive magnetic field probes (e.g., nuclear magnetic resonance based magnetic field measurements). The presented methodology is scalable to bigger magnet designs. The MR magnet can be reproduced with off-the-shelf components and a 3D printer and no special tools are needed for construction. All design files and code to reproduce the results will be made available as open source hardware.

Download Full-text

Using electromagnetic field calculations to understand the complexity of magnetic resonance imaging (MRI) at high magnetic field strength

IEEE Antennas and Propagation Society International Symposium. 2001 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.01CH37229) ◽

10.1109/aps.2001.958872 ◽

2002 ◽

Author(s):

M.B. Smith ◽

C. Collins ◽

Qing Yang ◽

Jinghua Wang ◽

Wanzhan Liu

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Electromagnetic Field ◽

Magnetic Resonance ◽

Field Strength ◽

Magnetic Field Strength ◽

High Magnetic Field ◽

Resonance Imaging ◽

High Magnetic Field Strength ◽

Magnetic Resonance Imaging Mri

Download Full-text

Comparative magnetic field measurements for homogeneity adjustment of magnetic resonance imaging equipments

2017 11th International Conference on Measurement ◽

10.23919/measurement.2017.7983585 ◽

2017 ◽

Author(s):

I. Frollo ◽

P. Andris ◽

A. Krafcik ◽

D. Gogola ◽

T. Dermek

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Magnetic Resonance ◽

Field Measurements ◽

Resonance Imaging ◽

Magnetic Field Measurements

Download Full-text

Interelement Decoupling Strategies at UHF MRI

Frontiers in Physics ◽

10.3389/fphy.2021.717369 ◽

2021 ◽

Vol 9 ◽

Author(s):

Irena Zivkovic

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Signal To Noise Ratio ◽

Larmor Frequency ◽

Resonance Imaging ◽

Signal To Noise ◽

Ultrahigh Field ◽

Coil Arrays ◽

Noise Ratio ◽

Rf Signal

Moving to the ultrahigh field magnetic resonance imaging (UHF MRI) brought many benefits such as potentially higher signal-to-noise ratio, contrast-to-noise ratio, and improved spectral resolution. The UHF MRI regime also introduced some challenges which could prevent full exploitation of mentioned advantages. A higher static magnetic field means increase in Larmor frequency, which further implies the shorter wavelength in a tissue. The shorter wavelength causes interferences of the RF signal and inhomogeneous excitation, which can be partially resolved by the introduction of the multichannel coil arrays. The biggest problem in UHF multichannel densely populated arrays is the existence of the interelement coupling, which should be minimized as much as possible. This article presents the nonconventional, recently developed decoupling techniques used in UHF MRI.

Download Full-text

Magnetic resonance imaging: effects of magnetic field strength.

Radiology ◽

10.1148/radiology.151.1.6701302 ◽

1984 ◽

Vol 151 (1) ◽

pp. 127-133 ◽

Cited By ~ 57

Author(s):

L E Crooks ◽

M Arakawa ◽

J Hoenninger ◽

B McCarten ◽

J Watts ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Magnetic Resonance ◽

Field Strength ◽

Magnetic Field Strength ◽

Resonance Imaging

Download Full-text

MRI Susceptibility Artefacts Related to Scaphoid Screws: the Effect of Screw Type, Screw Orientation and Imaging Parameters

Journal of Hand Surgery (European Volume) ◽

10.1054/jhsb.2001.0717 ◽

2002 ◽

Vol 27 (2) ◽

pp. 165-170 ◽

Cited By ~ 30

Author(s):

M. GANAPATHI ◽

G. JOSEPH ◽

R. SAVAGE ◽

A. R. JONES ◽

B. TIMMS ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Titanium Alloy ◽

Magnetic Resonance ◽

Main Magnetic Field ◽

Resonance Imaging ◽

Metal Implants ◽

Imaging Parameters ◽

Susceptibility Artefact

Metal implants produce susceptibility artefacts in magnetic resonance imaging. We have explored the effects of scaphoid screw characteristics and orientation on MR susceptibility artefact. Titanium alloy, smallness and longitudinal alignment with the z-axis of the main magnetic field reduce the size of the susceptibility artefact.

Download Full-text