| 日 時 | 2024年02月22日(木) 10:00 より 11:45 まで |
|---|---|
| 講演者 | Myung Kyun Woo 博士 |
| 講演者所属 | Assistant Professor, Division of Biomedical Engineering, Hankuk University of Foreign Studies, Republic of Korea |
| 場 所 | Zoomオンライン |
| お問い合わせ先 | 福永雅喜（生体機能情報解析室） fuku@nips.ac.jp |
| 要旨 |
Fundamentally, the physics of magnetic resonance imaging (MRI) dictates that the achievable signal-to-noise ratio (SNR) increases with magnetic field strength. Hence, ultra- high field (UHF) MRIs at 7 tesla (T) and above can yield higher resolution images or faster acquisition times over conventional high-field MRIs of 1.5 T or 3 T. Currently, a 10.5 T/447 MHz MRI system at University of Minnesota is the highest fully operational whole human body MRI scanner and is at the forefront of the MRI hardware technology. Since the wavelength at 447 MHz (in the presence of human tissue) is within the dimension of the imaging subject, unique challenges, particularly related to overall field homogeneity, arise at UHF, and the design of radiofrequency (RF) coil arrays for MRI applications benefits from serious consideration of antenna concepts. This is a significant change from the strict near-field regime-dominated RF coil arrays operating at clinical MRI frequencies below 3 T/128 MHz. At UHF frequencies, radiative-type antennas, particularly dipole antennas, have been suggested as excellent building blocks for transmit arrays and have, indeed, shown promising performance. Compared to other coil types, such as loop or microstrip antennas, dipole antennas have the additional advantage of symmetric B1+- field (defined as the transmit magnetic field generated by an RF coil) patterns, as well as a favorable direction of energy propagation (Poynting vector), which results in greater penetration depth. Consequently, both dipole antennas and the combination of loops with dipole antennas have been successfully used for UHF human imaging applications with high penetration, efficiency, and SNR. However, for realistic head array housings, the coaxial feed cables for dipole antennas have to be routed in close proximity to one leg of the dipole and they interact with the antenna elements. In recent research, we had started to evaluate and compare multiple innovative antenna arrays for UHF arrays. We compared the B1+ efficiency (defined as B1+ -field normalized by the square root of net input power) and specific absorption rate (SAR) efficiency (defined as B1+/√(peak 10 g SAR)) of the multiple arrays with the phantom. Finally, we compared the performance of these arrays with a human model. |
