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CURATOR
A pinboard by
Myung Kyun Woo

Research assistant, University of Minnesota/ Center for Magnetic Resonance Research (CMRR)

PINBOARD SUMMARY

A loop+dipole transceiver antenna array was designed for 447 MHz /10.5 tesla human head imaging.

Magnetic resonance imaging (MRI) is one of the invasive techniques for human imaging without any radioactive materials. Especially, ultra-high field (UHF) MRI, such as 10.5 tesla (T) MRI, provides a high signal-to noise ratio (SNR) which allows high resolution anatomical MRI and functional MRI (fMRI). To transmit and receive the signal for MRI, radiofrequency (RF) coil plays the role as the medium between the MRI machine and the human subject. The magnetic field called “B field” is generated by RF coils. Without RF coil development, none of MRI researches could have shown such substantial results we see nowadays. One thing we have to accept is that at 10.5T, the human body shows a short wavelength, and due to this, a significantly non-uniform B field distribution of RF coils results. Arrays consisting of transmit antennas have the ability to mitigate these non-uniformity through optimal combinations of phase and amplitude of the RF excitation waveform. For UHF applications, arrays are essentially required to achieve acceptable B field uniformity and optimized transmit efficiency. A combined loop and dipole antenna structure we developed is predicted to yield optimal RF transmitter performance for 10.5T human brain imaging. Loop is one of the efficient coil types for MRI. Recently, a new design of array coil based on a radiative antenna, such as a dipole antenna array, has been proposed to address the challenges of currently available loop array coil. In my research, I am combining a loop array and a dipole antenna array. This concept of combination is possible from the orthogonal B field generation of loop and dipole antenna. To investigate this for various geometries, we evaluated a geometrically adjustable 16-channel loop+dipole antenna array both through simulations and experiments on a human head size phantom. This combined loop+dipole antenna array includes benefits from both loop and dipole antenna array. Since RF coil is the electrical machine, going through simulation process is essential for the safety issue. For the safety, we calculated specific absorption rate (SAR) of this coil at 10.5T by simulation using the finite-difference time-domain (FDTD) method.

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