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U-shaped Ladder TEM-Coil Structure with Truncated Sensitivity Profile in z-Direction for High Field MRI
Conventional TEM-coils [1] come with a sensitivity profile and field-of view (FOV) that is largely extended in the z-direction comparedwith birdcage coils (BC) [2]. There is an analog situation when comparing TEM coil arrays [3] and degenerate birdcages (DBC) [4]. The excess z-FOV leads to safety issues with respect to the specific absorption rate (SAR). Moreover, it reduces image quality due to additional sensitivity to noise pickup [5, 6] and back-folding. We present anovel TEM coil with modified geometry, which has the strip sectionof each TEM coil element extended laterally at both ends before connecting to the RF screen. We call this coil type UTEM, due to the U-shape of the individual elements. Each of these lateral extensions has been found to produce transversal B1 field at the isocenter resulting in a steeper sensitivity profile along the z-axis and thus partially compensating the drawback of a traditional TEM element. Compared with a birdcage resonator, which is a floating RF structure resulting in e.g. the requirement of baluns for feeding, the defined RF ground of the TEM provides a solid reference for detuning circuits, feeding cables and pick-up coils used for RF-safety purposes.
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