Hadamard-encoding combined with two-dimensional-selective radiofrequency excitations for flexible and efficient acquisitions of multiple voxels in MR spectroscopy

Abstract

Purpose: 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. Materials and Methods: 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. Results: 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. Conclusion: 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. © 2011 Wiley Periodicals, Inc.