Design of a radiative surface coil array element at 7 T: The single‐side adapted dipole antenna

Abstract

Ultra high field MR imaging (≥7 T) of deeply located targets in the body is facing some radiofrequency‐field related challenges: interference patterns, reduced penetration depth, and higher Specific Absorbtion Ratio (SAR) levels. These can be alleviated by redesigning the elements of the transmit or transceive array. This is because at these high excitation field (B1) frequencies, conventional array element designs may have become suboptimal. In this work, an alternative design approach is presented, regarding coil array elements as antennas. Following this approach, the Poynting vector of the element should be oriented towards the imaging target region. The single‐side adapted dipole antenna is a novel design that fulfills this requirement. The performance of this design as a transmit coil array element has been characterized by comparison with three other, more conventional designs using finite difference time domain (FDTD) simulations and B +1 measurements on a phantom. Results show that the B +1 level at the deeper regions is higher while maintaining relatively low SAR levels. Also, the B +1 field distribution is more symmetrical and more uniform, promising better image homogeneity. Eight radiative antennas have been combined into a belt‐like surface array for prostate imaging. T1‐weighted (T1W) and T2‐weighted (T2W) volunteer images are presented along with B +1 measurements to demonstrate the improved efficiency. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

Magnetic resonance thermometry: Methodology, pitfalls and practical solutions

“…This justifies the use of birdcage type RF coils for transmission and loop RF coils for reception at lower fields (B0≤3.0T), while dipole antennas are well suited as transmit/receive elements for UHF MRI at B0≥7.0T (31,(119)(120)(121) and above (122). The usage of dipole or "dipole-like" antennas as a targeted RF heating device is very well recognized by the hyperthermia community (104,(126)(127)(128).…”

Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond

“…To address this obstacle multi-element transceiver coil arrays have been developed. These developments took advantage of building blocks that include stripline elements (34)(35)(36)(37)(38), dielectric resonant antennae (39), loop elements (40)(41)(42)(43)(44)(45)(46) and electrical dipoles (47)(48)(49)(50)(51)(52)(53).…”

“…Electrical dipole antennae were reported to provide a valuable alternative to traditional loop coils or stripline elements (47). Dipole antennae exhibit a simple RF antenna design with good directivity where the Poynting vector is perpendicular to the dipole length.…”

Safety of Ultra-High Field MRI: What are the Specific Risks?

“…This rapid growth in the number of UHF-MRI sites has quickly led to the development of scanning protocols [1][2][3] and the required hardware (brain [4][5][6], cardiac [7,8], body [9,10], spine [11,12], breast [13,14], and eye [15] ) to enable the use of UHF-MRI in both fundamental and clinical research studies as well as in pilot studies for pure clinical use [16][17][18]. A recent review article provides a comprehensive overview of the current status of high field MRI [19 •• ].…”