A flexible 32-channel receive array combined with a homogeneous transmit coil for human lung imaging with hyperpolarized 3He at 1.5 T.

ABSTRACT

Parallel imaging presents a promising approach for MRI of hyperpolarized nuclei, as the penalty in signal-to-noise ratio typically encountered with (1)H MRI due to a reduction in acquisition time can be offset by an increase in flip angle. The signal-to-noise ratio of hyperpolarized MRI generally exhibits a strong dependence on flip angle, which makes a homogeneous B(1)(+) transmit field desirable. This paper presents a flexible 32-channel receive array for (3) He human lung imaging at 1.5T designed for insertion into an asymmetric birdcage transmit coil. While the 32-channel array allows parallel imaging at high acceleration factors, the birdcage transmit coil provides a homogeneous B(1)(+) field. Decoupling between array elements is achieved by using a concentric shielding approach together with preamplifier decoupling. Coupling between transmit coil and array elements is low by virtue of a low geometric coupling coefficient, which is reduced further by the concentric shields in the array. The combination of the 32-channel array and birdcage transmit coil provides (3)He ventilation images of excellent quality with similar signal-to-noise ratio at acceleration factors R = 2 and R = 4, while maintaining a homogeneous B(1)(+).