Radiative losses of a birdcage resonator

Harpen, Michael D.

doi:10.1002/mrm.1910290522

Cited by 28 publications

(34 citation statements)

References 6 publications

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“…The challenging issue for high field (>100 MHz) large volume coils (>6000 cm 3 ) is the variable coil-subject interaction that significantly changes the field distribution and resonance frequency of the coil. In addition, the radiation loss from the coil to the environment increases drastically with field strength (10,11). Due to the short wavelength at high Larmor frequencies (20 cm for protons at 4T), far field effects cannot be ignored.…”

Section: Introductionmentioning

confidence: 99%

The design and test of a new volume coil for high field imaging

Wen

Chesnick

Balaban

1994

Magnetic Resonance in Med

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A major problem in the development of high field (>100 MHz) large volume (>6000 cm 3 ) MR coils is the interaction of the coil with the subject as well as the radiation loss to the environment. To reduce subject perturbation of the coil resonance modes, a volume coil that uses an array of freely rotating resonant elements radially mounted between two concentric cylinders was designed for operation at 170 MHz. Substantial electromagnetic energy is stored in the resonant elements outside the sample region without compromising the efficiency of the overall coil. This stored energy reduces the effect of the subject on the circuit and maintains a high Q, facilitating the tuning and matching of the coil. The unloaded O of the coil is 680; when loaded with a head, it was 129. The ratio of 5.3 of the unloaded to loaded Q supports the notion that the efficiency of the coil was maintained in comparison with previous designs. The power requirement and signal-to-noise performance are significantly improved. The coil is tuned by a mechanism that imparts the same degree of rotation on all of the elements simultaneously, varying their degree of mutual coupling and preserving the overall coil symmetry. A thin radiofrequency shield is an integral part of the coil to reduce the radiation effect, which is a significant loss mechanism at high fields. MR images were collected at 4T using this coil design with high sensitivity and B 1 homogeneity.

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Section: Introductionmentioning

confidence: 99%

The design and test of a new volume coil for high field imaging

Wen

Chesnick

Balaban

1994

Magnetic Resonance in Med

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“…Each side was constructed on a 170 × 170 mm 2 acrylic frame (Figure 1A). Two sides were then assembled with a 127 × 170 × 170 mm 3 copper shield box to decrease the radiation loss and increase RF efficiency [38] (green dotted line in Figure 1B). Approximate lengths of the matching and the tuning rods that need to be inserted in their respective outer struts were calculated using full wave FDTD simulations.…”

Section: Methodsmentioning

confidence: 99%

Experimental and numerical analysis of B 1 + field and SAR with a new transmit array design for 7 T breast MRI

Kim

Krishnamurthy

Santini

et al. 2016

Journal of Magnetic Resonance

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“…Due to the presence of end ring RF currents, split birdcage coils require a continuous electrical connection between two halves of the coil [1]. Additionally, most high-field (>3 T) head-sized RF coils use a shield surrounding the entire coil to decrease radiation losses [2]. For shielded RF coils, both the birdcage coil and the shield must be separated and reliably reconnected electrically during each use, which complicates both the fabrication and utilization.…”

Section: Introductionmentioning

confidence: 99%

4T split TEM volume head and knee coils for improved sensitivity and patient accessibility

Avdievich

Bradshaw

Lee

et al. 2007

Journal of Magnetic Resonance

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Split RF coils offer improved patient access by eliminating the need for the coil to be slid over the region of interest. For unshielded birdcage coils, the presence of end ring currents necessitates a direct electrical connection between two halves of the coil. For high-field (>3T) shielded birdcage coils, both the shield and the coil must be split and reliably connected electrically. This problem can be circumvented by the use of split TEM volume coils. Since the elements of a TEM coil are coupled inductively, no direct electrical connection between the halves is necessary. In this work we demonstrate that the effects of splitting the shield for head and knee TEMs can be compensated for, and performance retained. For the knee, the improved access allowed the coil diameter to be reduced, enhancing the sensitivity by 15-20%.

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Radiative losses of a birdcage resonator

Cited by 28 publications

References 6 publications

The design and test of a new volume coil for high field imaging

The design and test of a new volume coil for high field imaging

Experimental and numerical analysis of B 1 + field and SAR with a new transmit array design for 7 T breast MRI

4T split TEM volume head and knee coils for improved sensitivity and patient accessibility

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