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RISS 인기검색어
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- 저자 : Phil Heo(허필) (검색결과 1 건)
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Influences of RF Transmit Field (B₁+) of Un-shielded Birdcage Coil at 7 Tesla
Phil Heo(허필),Sun Young Chae(채선영),Julius Juhyun Chung(정주현),Jung Hee Lee(이정희) 대한전기학회 2014 정보 및 제어 심포지엄 논문집 Vol.2014 No.10
Despite the effect of radio frequency (RF) shield on the birdcage coil leading to degradation of RF signal sensitivity in the imaging region, RF shield has to be considered for preventing the electro-magnetic field interaction between RF coil and MR scanner. Although the RF shield decreases overall transverse magnetic field (B₁) and RF transmit (B₁+) sensitivity compared to un-shielded volume coil, optimal RF shield configuration and positioning are critical issues in small-animal MR scanner. In this study, we demonstrated that improper positioning of un-shield RF birdcage (BC) coil leads to inhomogeneous B₁ + distribution at 7 Tesla. The flip angle (FA) map and the S-parameter measurement of custom-built 8-leg BC coil were performed when rotating its coil by 5° in the azimuthally angle. The results clearly show that an inhomogeneous FA map was measured in all cases due to the coil-subject interaction and improper positioning of BC coil. The mean valuesfor reference angles at 55°, +100° and + 220° of BC coil were 56.9, 54.5 and 58.3, respectively. Standard deviation (SD) value of for reference angles at 55°, +100° and + 220° of BC coil were measured to be 2.5, 2.7 and 2.3. The differentiation of mean and SD value of rotating angles indicate inhomogeneity and their sensitivity of B₁+ field. The proper positioning of BC coil in the MR scanner is crucial in shielding RF in the small-animal MR scanner.
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