scholarly journals Magnetic Resonance-Electrical Properties Tomography by Directly Solving Maxwell’s Curl Equations

2020 ◽  
Vol 10 (9) ◽  
pp. 3318
Author(s):  
Jieru Chi ◽  
Lei Guo ◽  
Aurelien Destruel ◽  
Yaohui Wang ◽  
Chunyi Liu ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Electrical Properties ◽  
Graphics Processing Unit ◽  
Field Measurements ◽  
Processing Unit ◽  
Field Calculation ◽  
Resonance Imaging ◽  
Equation Problem ◽  
Magnetic Resonance Imaging Mri

Magnetic Resonance-Electrical Properties Tomography (MR-EPT) is a method to reconstruct the electrical properties (EPs) of bio-tissues from the measured radiofrequency (RF) field in Magnetic Resonance Imaging (MRI). Current MR-EPT approaches reconstruct the EP profile by solving a second-order partial differential wave equation problem, which is sensitive to noise and can induce large reconstruction artefacts near tissue boundaries and areas with inaccurate field measurements. In this paper, a novel MR-EPT approach is proposed, which is based on a direct solution to Maxwell’s curl equations. The distribution of EPs is calculated by iteratively fitting the RF field calculated by the finite-difference-time-domain (FDTD) technique to the measured values. To solve the time-consuming problem of the iterative fitting, a graphics processing unit (GPU) is used to accelerate the FDTD technique to process the field calculation kernel. The new EPT method was evaluated by investigating a numerical head phantom, and it was found that EP values can be accurately calculated and were relatively insensitive to simulated RF field errors. The feasibility of the proposed method was further validated using phantom-based experimental data collected from a 9.4 Tesla (T) Magnetic Resonance Imaging (MRI) system. The results also indicated that more accurate EP values could be reconstructed from the new method compared with conventional methods. Moreover, even in the absence of phase information of the RF field, the proposed approach is still capable of offering robust EPT solutions, thus having improved practicality for potential clinical applications.

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

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.

Top-Ten Tips for Imaging the Brachial Plexus with Ultrasound and MRI

2019 ◽  
Vol 23 (04) ◽  
pp. 405-418 ◽  
Author(s):  
James F. Griffith ◽  
Radhesh Krishna Lalam
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Brachial Plexus ◽  
Muscle Denervation ◽  
Resonance Imaging ◽  
Neural Injury ◽  
Clinical Indications ◽  
Magnetic Resonance Imaging Mri ◽  
High Level ◽  
Extensive Involvement

AbstractWhen it comes to examining the brachial plexus, ultrasound (US) and magnetic resonance imaging (MRI) are complementary investigations. US is well placed for screening most extraforaminal pathologies, whereas MRI is more sensitive and accurate for specific clinical indications. For example, MRI is probably the preferred technique for assessment of trauma because it enables a thorough evaluation of both the intraspinal and extraspinal elements, although US can depict extraforaminal neural injury with a high level of accuracy. Conversely, US is probably the preferred technique for examination of neurologic amyotrophy because a more extensive involvement beyond the brachial plexus is the norm, although MRI is more sensitive than US for evaluating muscle denervation associated with this entity. With this synergy in mind, this review highlights the tips for examining the brachial plexus with US and MRI.

Use of Magnetic Resonance Imaging (MRI) to Determine the 3D Geometry in the Human Rectum

Endoscopy ◽  
2004 ◽  
Vol 36 (10) ◽  
Author(s):  
BP McMahon ◽  
JB Frøkjær ◽  
A Bergmann ◽  
DH Liao ◽  
E Steffensen ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Resonance Imaging ◽  
3D Geometry ◽  
Human Rectum ◽  
Magnetic Resonance Imaging Mri

Magnetic resonance imaging in study of lungs

2019 ◽  
pp. 10-23
Author(s):  
T. A. Akhadov ◽  
S. Yu. Guryakov ◽  
M. V. Ublinsky
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Medical Society ◽  
Resonance Imaging ◽  
Iodinated Contrast ◽  
Long Time ◽  
Women And Children ◽  
Magnetic Resonance Imaging Mri ◽  
A Current ◽  
Lung Mri

For a long time, there was a need to apply magnetic resonance imaging (MRI) technique for lung visualization in clinical practice. The development of this method is stimulated by necessity of the emergence of an alternative to computed tomography, especially when radiation and injection of iodine-containing contrast agents are contraindicated or undesirable, for example, in pregnant women and children, people with intolerance to iodinated contrast. One of the reasons why lung MRI is still rarely used is lack of elaborated standardized protocols that would be adapted to clinical needs of medical society. This publication is a current literature review on the use of MRI in lung studies.

26. Nothing but the truth, so help me God: The history of magnetic resonance imaging

2007 ◽  
Vol 30 (4) ◽  
pp. 41
Author(s):  
A. Dechant
Keyword(s):  
Magnetic Resonance Imaging ◽  
New York ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nobel Prize ◽  
Resonance Imaging ◽  
Solid State Physics ◽  
Magnetic Resonance Imaging Mri ◽  
The Times ◽  
Nuclear Magnetic

On the morning of October 10, 2003, the residents of New York awoke to find that an entire page of their beloved paper, The Times, had been usurped for the sole purpose of flagrant self-promotion and protestation. On his own behalf, Dr. Raymand Damadian had purchased a one page spread bemoaning his exclusion in the Nobel Prize for Medicine that year which had previously been awarded to Paul Laterbur and Peter Mansfield for their contributions to the development of Magnetic Resonance Imaging (MRI). Over the course of the next few months, the public was to witness a series of such articles proclaiming that a shameful wrong had been committed, and that the truth would eventually prove Dr. Damadian’s accusations. That truth lay in the early theoretical and technical foundations that led to the discovery of MRI. Described just after the Second World War, nuclear magnetic resonance (NMR) was hailed as a breakthrough in physical chemistry for which Felix Bloch and Edward Purcell were awarded the Nobel Prize in Physics in 1952. Two decades later, in 1971, Dr. Damadian discovered that differences between the NMR signals of cancerous and normal tissue might provide a rapid means of cancer detection. However, Laterbur and Mansfield were the first to actually demonstrate images of live tissue using the application of magnetic gradients – the key to modern MRI. Though speculation exists that Dr. Damadian may have been excluded from the prize due to his religious beliefs or political rivalry, only time will reveal the whole truth when the Nobel files are opened 50 years hence. Bradley W. The Nobel Prize: Three Investigators Allowed but Two Were Chosen. Journal of Magnetic Resonance Imaging 2004; 19:520. Laterbur P. Image formation by induced local interactions: examples of employing nuclear magnetic resonance. Nature 1973; 242:190-191. Mansfield P, Grannell P. “NMR diffraction in solids?” Journal of Physics C: Solid State Physics 1973; 63:L433-L426.

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