TY - JOUR
T1 - Extending a Birdcage Coil for Magnetic Resonance Imaging of a Human Head with an Artificial Magnetic Shield
AU - Lezhennikova, Kseniia
AU - Simovski, C.
AU - Abdeddaim, R.
AU - Balafendiev, R.
AU - Glybovski, S.
PY - 2021/2
Y1 - 2021/2
N2 - In magnetic resonance imaging, a birdcage coil is the most commonly used volumetric resonator creating a highly homogeneous radiofrequency magnetic field in a conductive sample. An artificial magnetic radiofrequency shield was recently shown to improve the magnetic field amplitude per unit power (transmit efficiency) of a preclinical birdcage coil by reducing the intrinsic losses in the coil and increasing power absorbed by the sample. In this paper, we propose a new application of an artificial shield in clinical MRI. Thanks to the proposed artificial shield a birdcage coil for human brain imaging operating at 300 MHz (Larmor frequency of protons at static fields of 7 T) can be expanded to increase free space. As a result, the coil becomes more comfortable for the patient and keeping comparable transmit efficiency. The same extended coil with a conventional copper shield would have at least 10% lower efficiency. The proposed artificial shield is implemented as an annular-ring cavity-backed slot in a copper cylinder that tightly surrounds the birdcage. To demonstrate the effect, radiofrequency magnetic field and specific absorption rate distributions were compared numerically and experimentally for the initial and extended coils with different shields.
AB - In magnetic resonance imaging, a birdcage coil is the most commonly used volumetric resonator creating a highly homogeneous radiofrequency magnetic field in a conductive sample. An artificial magnetic radiofrequency shield was recently shown to improve the magnetic field amplitude per unit power (transmit efficiency) of a preclinical birdcage coil by reducing the intrinsic losses in the coil and increasing power absorbed by the sample. In this paper, we propose a new application of an artificial shield in clinical MRI. Thanks to the proposed artificial shield a birdcage coil for human brain imaging operating at 300 MHz (Larmor frequency of protons at static fields of 7 T) can be expanded to increase free space. As a result, the coil becomes more comfortable for the patient and keeping comparable transmit efficiency. The same extended coil with a conventional copper shield would have at least 10% lower efficiency. The proposed artificial shield is implemented as an annular-ring cavity-backed slot in a copper cylinder that tightly surrounds the birdcage. To demonstrate the effect, radiofrequency magnetic field and specific absorption rate distributions were compared numerically and experimentally for the initial and extended coils with different shields.
KW - Ultra-high field MRI
KW - Magnetic shield
KW - Human head MRI
KW - Birdcage coil
UR - http://www.scopus.com/inward/record.url?scp=85099242535&partnerID=8YFLogxK
U2 - 10.1016/j.photonics.2020.100890
DO - 10.1016/j.photonics.2020.100890
M3 - Article
SN - 1569-4410
VL - 43
JO - Photonics and Nanostructures - Fundamentals and Applications
JF - Photonics and Nanostructures - Fundamentals and Applications
M1 - 100890
ER -