Abstract
We describe an actively shielded cylindrical RF transmit coil producing a highly uniform internal field (±0.5%) over an extended volume and a strongly suppressed (÷20) external field. Direct field mapping and experimental checks using in-situ NMR and MRI of polarised 3He at low temperature demonstrate performance consistent with numerical field computations.
Highlights
Obtaining highly uniform RF fields over extended volumes is mandatory for pulsed NMR and MRI experiments requiring accurate tipping angles
Eddy currents may result in significant heating of surrounding conductors, which must be avoided in low temperature experiments
The eddy currents can be actively reduced using a surrounding shield coil designed for this purpose [4]
Summary
Obtaining highly uniform RF fields over extended volumes is mandatory for pulsed NMR and MRI experiments requiring accurate tipping angles. This requirement may occur, for instance, when series of fixed or variable smallangle flips are used in hyperpolarised samples. The large RF field outside such coils may induce eddy currents in neighbouring conductors and affect RF field uniformity. Eddy currents may result in significant heating of surrounding conductors, which must be avoided in low temperature experiments. The eddy currents can be actively reduced using a surrounding shield coil designed for this purpose [4]
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