Hadamard-encoding combined with two-dimensional-selective radiofrequency excitations for flexible and efficient...

To improve the efficiency and flexibility of acquisitions of multiple voxels in MR spectroscopy by combining two-dimensional-selective radiofrequency (2DRF) excitations and Hadamard encoding.

With 2DRF excitations (PROPELLER trajectory, 16 half-Fourier segments, each with five lines) two voxels are defined. By combining the individual 2DRF pulses with Hadamard-like encoded phases, the voxels are acquired simultaneously but the individual contributions can be isolated from the obtained spectra. This is demonstrated on a 3 Tesla whole-body MR system in phantoms and in the human brain in vivo.

Compared with sequential single-voxel acquisitions the signal efficiency increases with the number of voxels covered. Furthermore, in comparison to conventional single-voxel MRS based on cross-sectional RF excitations, 2DRF excitations offer a higher flexibility because they allow for arbitrary voxel sizes, orientations, in-plane positions, and shapes.

The presented approach improves the flexibility and efficiency of acquisitions of multiple voxels, i.e., can shorten acquisition times accordingly, and can help to reduce partial volume effects.