Radiative RF antenna arrays for cardiac, brain and thermal magnetic resonance at ultrahigh and extreme magnetic field strengths: Concepts, electromagnetic field simulations and applications

2017 ◽  
Author(s):  
Thoralf Niendorf ◽  
Celal Oezerdem ◽  
Yiyi Ji ◽  
Eva Oberacker ◽  
Andre Kuehne ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Magnetic Resonance ◽  
Antenna Arrays ◽  
Rf Antenna ◽  
Field Strengths

A 4 × 4 array multichannel magnetic stimulation system using submillimeter sized planar square spiral coils: The spatial distribution of electromagnetic field

2022 ◽  
pp. 1-18
Author(s):  
Lei Tian ◽  
Limei Song ◽  
Yu Zheng ◽  
Jinhai Wang
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Spatial Distribution ◽  
Field Strength ◽  
Electric Field ◽  
Magnetic Stimulation ◽  
Spiral Coil ◽  
Average Magnetic Field ◽  
Stimulation System ◽  
Field Strengths

Multi-coil magnetic stimulation has advantages over single-coil magnetic stimulation, such as more accurate targeting and larger stimulation range. In this paper, a 4 × 4 array multichannel magnetic stimulation system based on a submillimeter planar square spiral coil is proposed. The effects of multiple currents with different directions on the electromagnetic field strength and the focusing zone of the array-structured magnetic stimulation system are studied. The spatial distribution characteristics of the electromagnetic field are discussed. In addition, a method is proposed that can predict the spatial distributions of the electric and magnetic fields when currents in different directions are applied to the array-structured magnetic stimulation system. The study results show that in the section of z = 2 μm, the maximum and average magnetic field strengths of the array-structured magnetic stimulation system are 6.39 mT and 2.68 mT, respectively. The maximum and average electric field strengths are 614.7 mV/m and 122.82 mV/m, respectively, where 84.39% of the measured electric field values are greater than 73 mV/m. The average magnetic field strength of the focusing zone, i.e., the zone in between the two coils, is 3.38 mT with a mean square deviation of 0.18. Therefore, the array-structured multi-channel magnetic stimulation system based on a planar square spiral coil can have a small size of 412 μm × 412 μm × 1.7 μm, which helps improving the spatial distribution of electromagnetic field and increase the effectiveness of magnetic stimulation. The main contribution of this paper is a method for designing multichannel micro-magnetic stimulation devices.

scholarly journals Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment

Cancers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1720
Author(s):  
Haopeng Han ◽  
Thomas Wilhelm Eigentler ◽  
Shuailin Wang ◽  
Egor Kretov ◽  
Lukas Winter ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Radio Frequency ◽  
Cancer Treatment ◽  
Antenna Arrays ◽  
Power Level ◽  
Signal Generator ◽  
Rf Heating ◽  
Anti Cancer ◽  
Rf Antenna ◽  
Rf Channels

Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.

A quantum mechanical discussion of Rabi oscillations

2008 ◽  
Vol 86 (8) ◽  
pp. 953-960 ◽  
Author(s):  
G R Hoy ◽  
J Odeurs
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Quantum Mechanics ◽  
Magnetic Resonance ◽  
Spin System ◽  
Magnetic Moment ◽  
Time Dependent ◽  
Quantum Mechanical ◽  
Rabi Oscillations ◽  
Interaction Picture

In 1937, Rabi treated the problem of a magnetic moment in an applied time-dependent magnetic field. This became the well-known magnetic resonance situation. The Hamiltonian is often taken to be [Formula: see text] = – µ · [[Formula: see text]]. In this paper, the Rabi oscillations formula, describing the spin flipping, is derived in an unusual way. The method uses a modification of a method due to Heitler. In the Heitler method, one uses the Interaction Picture of quantum mechanics. Due to the time-dependence in the problem, the usual Heitler method fails. However, the solution is found after quantizing the electromagnetic field. To better understand the origin of the spin flipping, the analogous time-independent problem is also solved. It is made clear that the origin of the Rabi oscillations is not due to the time-dependent magnetic field. The spin flipping is essentially due to the fact that the spin system, when initially prepared, is not in an eigenstate of the Hamiltonian. Thus, as times progresses, the system naturally evolves through the noneigenstate basis states.PACS Nos.: 03.65.–w, 76.20.+q

Putaminal magnetic resonance imaging features at various magnetic field strengths in multiple system atrophy

2010 ◽  
Vol 25 (12) ◽  
pp. 1916-1923 ◽  
Author(s):  
Hirohisa Watanabe ◽  
Mizuki Ito ◽  
Hiroshi Fukatsu ◽  
Jo Senda ◽  
Naoki Atsuta ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Field ◽  
Magnetic Resonance ◽  
Multiple System Atrophy ◽  
Imaging Features ◽  
Resonance Imaging ◽  
Field Strengths

scholarly journals Novel Magnetic Resonance Acquisition and Processing Strategies for Biological Tissue Characterisation

2021 ◽  
Author(s):  
◽  
Fangrong Zong
Keyword(s):  
Magnetic Field ◽  
Principal Component Analysis ◽  
Magnetic Resonance ◽  
Compressed Sensing ◽  
Fractional Anisotropy ◽  
Principal Component ◽  
Component Analysis ◽  
Tissue Characterisation ◽  
Diffusion Weighted ◽  
Field Strengths

<p>Proton magnetic resonance techniques have become indispensable for characterising tissues non-invasively. These methods provide abundant information regarding metabolism, morphology and histology of the sample under study. While these techniques were more expensive in the past compared to radioactive methods, modern advances in hardware and methodology provide the potential to use magnetic resonance systems more efficiently and widely. In this context, this thesis explored innovative magnetic resonance technologies from three independent perspectives which are suitable for tissue characterisation, utilising techniques from a wide range of disciplines including physics, engineering, biology and medical sciences.  One strategy relates to compressed sensing magnetic resonance imaging, seeking to recover detailed features at high undersampling rates. A data-adaptive sparse transform facilitated by principal component analysis was introduced as an alternative to the conventional pre-defined sparse transform. Moreover, the principal component analysis was used in a recognition algorithm for the reconstruction of undersampled data. The performances of these approaches were studied in cases of localised changes in the acquired images. The results demonstrated that the recognition reconstruction algorithm performed better than wavelet compressed sensing. This progress can be utilised to accelerate current state of the art imaging protocols at high magnetic field strengths. Furthermore, the prior knowledge contained in high resolution databases may enhance imaging capabilities of technologies at low magnetic field strengths.  A second approach exploits nuclear magnetic resonance diffusion contrast instead of contrast agents for tissue characterisation. Microstructural information and global fractional anisotropy can be obtained from diffusion-diffusion correlation spectroscopy via a novel multi-dimensional gradient scheme. The concept was validated by random walk simulations and experiments of biological samples. Both correlation maps and global fractional anisotropy of in vitro healthy and tumour-bearing mouse brains were found to be different, thus providing a potential application of the proposed scheme in diffusion oncology.  In addition, a threshold algorithm on the selection of a region of interest was implemented to minimise inter-observer variations. This technique was applied to a pilot study of diffusion weighted imaging data which were acquired from patients after x-ray mammography indicated lesions. The statistical analysis revealed an optimal threshold similar to values commonly used in positron emission tomography. Apart from selecting regions automatically, various data processing methods were implemented and compared with each other regarding their diagnostic accuracies. This field study provides opportunities for standardising procedures in diffusion weighted mammography, which may be integrated into clinical analysis in the future.</p>

The eigenvalues of electromagnetic angular momentum

1936 ◽  
Vol 32 (4) ◽  
pp. 614-621 ◽  
Author(s):  
M. H. L. Pryce
Keyword(s):  
Magnetic Field ◽  
Field Theory ◽  
Electromagnetic Field ◽  
Angular Momentum ◽  
Vector Potential ◽  
Charged Particles ◽  
Radial Component ◽  
Spin Angular Momentum ◽  
The Magnetic Field ◽  
Field Strengths

It is shown that the eigenvalues of the angular momentum of the electromagnetic field containing a number of charged particles, apart from spin angular momentum, are only the integral multiples of ħ. This is shown by using cylindrical polar variables, and taking a particular choice of the vector potential in which the radial component is zero, defined explicitly in terms of the magnetic field strengths. By expanding in terms of the Fourier functions einθ, the angular momentum is separated out into terms independent of one another, each taking on only integral values in units of ħ.The arguments all apply equally well to a modified field theory such as that of Born and Infeld.

scholarly journals Enhancing magnetic resonance imaging with contrast agents for ultra-high field strengths

The Analyst ◽  
2014 ◽  
Vol 139 (18) ◽  
pp. 4401-4410 ◽  
Author(s):  
Akhila N. W. Kuda-Wedagedara ◽  
Matthew J. Allen
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Field ◽  
Magnetic Resonance ◽  
Contrast Agents ◽  
High Magnetic Field ◽  
High Field ◽  
Resonance Imaging ◽  
Ultra High Field ◽  
New Strategies ◽  
Field Strengths

New strategies for contrast agents enable effective magnetic resonance imaging at ultra-high magnetic field strengths.

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