Imaging capabilities of the 1H-X-nucleus metamaterial-inspired multinuclear RF-coil

Conventionally, magnetic resonance imaging (MRI) is performed by pulsing gradient coils, which invariably leads to strong acoustic noise, patient safety concerns due to induced currents, and costly power/space requirements. This modeling study investigates a new silent, gradient coil-free MR imaging method, in which a radiofrequency (RF) coil and its nonuniform field (B1+) are mechanically rotated about the patient. The advantage of the rotatingB1+field is that, for the first time, it provides a large number of degrees of freedom to aid a successfulB1+image encoding process. The mathematical modeling was performed using flip angle modulation as part of a finite-difference-based Bloch equation solver. Preliminary results suggest that representative MR images with intensity deviations of <5% from the original image can be obtained using rotating RF field approach. This method may open up new avenues towards anatomical and functional imaging in medicine.

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An Antenna-Theory Method for Modeling High-Frequency RF Coils: A Segmented Birdcage Example

International Journal of Antennas and Propagation ◽

10.1155/2008/456019 ◽

2008 ◽

Vol 2008 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Xin Chen ◽

Victor Taracila ◽

Timothy Eagan ◽

Hiroyuki Fujita ◽

Xingxian Shou ◽

...

Keyword(s):

High Frequency ◽

Dipole Antenna ◽

Rf Coils ◽

Optimized Design ◽

Theory Method ◽

Rf Coil ◽

Field Approach ◽

Antenna Theory ◽

Target Field ◽

Tem Mode

We suggest that center-fed dipole antenna analytics can be employed in the optimized design of high-frequency MRI RF coil applications. The method is illustrated in the design of a single-segmented birdcage model and a short multisegmented birdcage model. As a byproduct, it is shown that for a long single-segmented birdcage model, the RF field within it is essentially a TEM mode and has excellent planar uniformity. For a short shielded multisegmented birdcage model, the RF field is optimized with a target-field approach with an average SAR functional. The planar homogeneity of the optimized RF field is significantly improved compared with that of a single-segmented birdcage model with the same geometry. The accuracy of the antenna formulae is also verified with numerical simulations performed via commercial software. The model discussed herein provides evidence for the effectiveness of antenna methods in future RF coil analysis.

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Numerical Analysis of a Flexible Dual Loop Coil and its Experimental Validation for pre-Clinical Magnetic Resonance Imaging of Rodents at 7 T

Measurement Science Review ◽

10.1515/msr-2016-0037 ◽

2016 ◽

Vol 16 (6) ◽

pp. 294-299 ◽

Cited By ~ 1

Author(s):

S. Solis-Najera ◽

F. Vazquez ◽

R. Hernandez ◽

O. Marrufo ◽

A.O. Rodriguez

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Resonance ◽

Imaging System ◽

Ex Vivo ◽

Small Animal ◽

Magnetic Resonance Imaging System ◽

External Diameter ◽

Rf Coil ◽

Resonance Imaging ◽

Clinical Magnetic Resonance Imaging

Abstract A surface radio frequency coil was developed for small animal image acquisition in a pre-clinical magnetic resonance imaging system at 7 T. A flexible coil composed of two circular loops was developed to closely cover the object to be imaged. Electromagnetic numerical simulations were performed to evaluate its performance before the coil construction. An analytical expression of the mutual inductance for the two circular loops as a function of the separation between them was derived and used to validate the simulations. The RF coil is composed of two circular loops with a 5 cm external diameter and was tuned to 300 MHz and 50 Ohms matched. The angle between the loops was varied and the Q factor was obtained from the S11 simulations for each angle. B1 homogeneity was also evaluated using the electromagnetic simulations. The coil prototype was designed and built considering the numerical simulation results. To show the feasibility of the coil and its performance, saline-solution phantom images were acquired. A correlation of the simulations and imaging experimental results was conducted showing a concordance of 0.88 for the B1 field. The best coil performance was obtained at the 90° aperture angle. A more realistic phantom was also built using a formaldehyde-fixed rat phantom for ex vivo imaging experiments. All images showed a good image quality revealing clearly defined anatomical details of an ex vivo rat.

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