Abstract:In this paper we address the possibility to perform imaging of two samples within the same acquisition time using coupled ceramic resonators and one transmit/receive channel. We theoretically and experimentally compare the operation of our ceramic dual-resonator probe with a wire-wound solenoid probe, which is the standard probe used in ultrahigh-field magnetic resonance microscopy. We show that due to the low-loss ceramics used to fabricate the resonators, and a favorable distribution of the electric field wi… Show more
“…However, as shown in Figure 8, this does not exclude certain block geometries from being used as an efficient RF antenna. We note that there could be other efficient feed mechanisms (or their combinations, given the fact that some of them are orthogonal) which could be used, for example, E x -k z (Figure 8) and should be investigated in the future [23][24][25][26][27][28].…”
Section: Discussionmentioning
confidence: 99%
“…In the context of our study, previous work can be divided into two groups: (a) reports in which different, mainly loop-coupled, dielectric structures were used with a clear motivation to induce desired dielectric modes [23][24][25][26]28] and (b) reports in which dielectric structures were used solely for the purpose of shortening dipole antennas [6,11,13,15,29,30]. In the case of (a), different types of dielectric modes were investigated, while in the case of (b), even if dielectric modes and their impact on antenna performance were considered by the authors, it was not mentioned in any of those reports.…”
Shortened dipole antennas based on rectangular dielectric blocks play an important role in ultrahigh field magnetic resonance imaging (UHF-MRI) radio frequency (RF) coil design. However, the generally assumed direct contact with the subject is difficult to maintain in typical in vivo settings. We have previously observed that certain dielectrically shortened dipole antennas can produce a substantially altered transmit field distribution with a very low transmit efficiency when the block and the sample are physically separated. Therefore, the aim of this study was to determine a) why certain designs of dielectrically shortened dipole antennas can produce an inefficient transmit field when the block and the sample are physically separated and b) how this depends on key parameters such as rectangular block geometry, dielectric constant, loading geometry, and RF feeding. In this work, two main types of quasi-transverse dielectric modes were found in different rectangular block geometries and interpreted as TE11δz (MR efficient) and TE1δδy (MR inefficient), and their impact on in vivo MRI experiments involving the human head, calf, and wrist was explored. This study shows, for the first time, why certain antennas preserve their transmit field efficiency despite physical separation from the sample. We conclude that the proposed approach has the potential to provide new insights into dipole antenna design for UHF-MRI.
“…However, as shown in Figure 8, this does not exclude certain block geometries from being used as an efficient RF antenna. We note that there could be other efficient feed mechanisms (or their combinations, given the fact that some of them are orthogonal) which could be used, for example, E x -k z (Figure 8) and should be investigated in the future [23][24][25][26][27][28].…”
Section: Discussionmentioning
confidence: 99%
“…In the context of our study, previous work can be divided into two groups: (a) reports in which different, mainly loop-coupled, dielectric structures were used with a clear motivation to induce desired dielectric modes [23][24][25][26]28] and (b) reports in which dielectric structures were used solely for the purpose of shortening dipole antennas [6,11,13,15,29,30]. In the case of (a), different types of dielectric modes were investigated, while in the case of (b), even if dielectric modes and their impact on antenna performance were considered by the authors, it was not mentioned in any of those reports.…”
Shortened dipole antennas based on rectangular dielectric blocks play an important role in ultrahigh field magnetic resonance imaging (UHF-MRI) radio frequency (RF) coil design. However, the generally assumed direct contact with the subject is difficult to maintain in typical in vivo settings. We have previously observed that certain dielectrically shortened dipole antennas can produce a substantially altered transmit field distribution with a very low transmit efficiency when the block and the sample are physically separated. Therefore, the aim of this study was to determine a) why certain designs of dielectrically shortened dipole antennas can produce an inefficient transmit field when the block and the sample are physically separated and b) how this depends on key parameters such as rectangular block geometry, dielectric constant, loading geometry, and RF feeding. In this work, two main types of quasi-transverse dielectric modes were found in different rectangular block geometries and interpreted as TE11δz (MR efficient) and TE1δδy (MR inefficient), and their impact on in vivo MRI experiments involving the human head, calf, and wrist was explored. This study shows, for the first time, why certain antennas preserve their transmit field efficiency despite physical separation from the sample. We conclude that the proposed approach has the potential to provide new insights into dipole antenna design for UHF-MRI.
“…24 . The approach can be extended using two coupled DRs, which were shown to be able to simultaneously image two samples with high sensitivity [ 105 ]. Fig.…”
Section: New Materials In Designing Transmit and Receive Resonatorsmentioning
This article reviews recent developments in designing and testing new types of materials which can be: (i) placed around the body for in vivo imaging, (ii) be integrated into a conventional RF coil, or (iii) form the resonator itself. These materials can improve the quality of MRI scans for both in vivo and magnetic resonance microscopy applications. The methodological section covers the basic operation and design of two different types of materials, namely high permittivity materials constructed from ceramics and artificial dielectrics/metasurfaces formed by coupled conductive subunits, either in air or surrounded by dielectric material. Applications of high permittivity materials and metasurfaces placed next to the body to neuroimaging and extremity imaging at 7 T, body and neuroimaging at 3 T, and extremity imaging at 1.5 T are shown. Results using ceramic resonators for both high field in vivo imaging and magnetic resonance microscopy are also shown. The development of new materials to improve MR image quality remains an active area of research, but has not yet found significant use in clinical applications. This is mainly due to practical issues such as specific absorption rate modelling, accurate and reproducible placement, and acceptable size/weight of such materials. The most successful area has been simple “dielectric pads” for neuroimaging at 7 T which were initially developed somewhat as a stop-gap while parallel transmit technology was being developed, but have continued to be used at many sites. Some of these issues can potentially be overcome using much lighter metasurfaces and artificial dielectrics, which are just beginning to be assessed.
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