Theoretical and experimental evaluation of detached endcaps for 3 T birdcage coils.
(2003)
Journal - Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine (United States )
Abstract :
The use of detached endcaps for 3 T birdcage coils was investigated both theoretically and experimentally. Finite difference time domain analysis, along with workbench and MRI techniques, were used to map the radiofrequency (RF) B(1) distribution along the coil axis with and without an endcap. Without an endcap the measured B(1) value at the service end of the birdcage was only 45% of the value at the coil's center. This was improved to 85% with a detached endcap of maximum achievable diameter (375 mm), positioned 4 mm from the RF shield. The B(1) field distribution on the patient side of the coil was unaffected by the presence of the endcap. The dependence of the B(1) distribution as a function of endcap diameter was also investigated. Surprisingly, simulations and experiments show that there is an optimum ratio of endcap-to-birdcage coil diameter (approximately 1.08) that gives the best B(1) homogeneity. In the human head the optimized endcap, positioned 16 mm from the RF shield, improves the MRI signal amplitude from 55% to 85% of maximum toward the service end. This novel endcap design is easy to implement with existing birdcage coils, and could prove useful when flexibility in access to the RF coil is required.Copyright 2003 Wiley-Liss, Inc.
| ISSN : | 0740-3194 |
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| Mesh Heading : | Equipment Design Head Humans Magnetic Resonance Imaging Phantoms, Imaging |
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| Mesh Heading Relevant : | anatomy & histology instrumentation |
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Characterization and reduction of gradient-induced eddy currents in the RF shield of a TEM resonator.
(2002)
Journal - Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine (United States )
Abstract :
Radiofrequency (RF) shields that surround MRI transmit/receive coils should provide effective RF screening, without introducing unwanted eddy currents induced by gradient switching. Results are presented from a detailed examination of an effective RF shield design for a prototype transverse electromagnetic (TEM) resonator suitable for use at 3 Tesla. It was found that effective RF shielding and low eddy current sensitivity could be achieved by axial segmentation (gap width = 2.4 mm) of a relatively thick (35 microm) copper shield, etched on a kapton polyimide substrate. This design has two main advantages: first, it makes the TEM less sensitive to the external environment and RF interference; and second, it makes the RF shield mechanically robust and easy to handle and assemble.Copyright 2002 Wiley-Liss, Inc.
| ISSN : | 0740-3194 |
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| Mesh Heading : | Electromagnetic Phenomena Magnetic Resonance Imaging Radio Waves methods |
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| Mesh Heading Relevant : | instrumentation |
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