Vincent Boer PhD, Abstract Co-Author: Nothing to Disclose

Dennis W. J. Klomp, Abstract Co-Author: Nothing to Disclose

Peter Blakeley Barker DPhil, Presenter: Research Consultant, Olea Medical

When performing MRS using multiple receiver coils, spatial information is inherently contained in the signal from each channel. Using this information, parallel reconstruction techniques can be used to separate spectra from multiple, simultaneously excited, regions. This study investigated the feasibility of Parallel Reconstruction Image Acquisition Mode (PRIAM) MRS of the human brain.

PRIAM experiments were performed on 3 normal volunteers using 3T or 7T Achieva (Philips Healthcare) systems equipped with 32-channel receive head coils. At 7T, sLASER localization with high bandwidth excitation pulses was used (TR/TE 4000/37ms, 3x1.5x1.5cm^3, 64 averages), while at 3T the PRESS sequence (2000/31ms) was used. Spectra were recorded from the left and right hippocampi. Dual volume excitation pulses were implemented as the scaled, complex summation of 2 slice selective pulses used for each individual location. PRIAM reconstruction using the SENSE algorithm was performed on data acquired both with and without VAPOR water suppression.

Figure 1 shows example spectra recorded from the left and right hippocampi at 7T. The spectral appearance of the PRIAM reconstruction (c, recorded in half the total scan time) is virtually identical to that of the individual excitations (a, b). Similar results were also obtained at 3T. Note also that the ‘out-of-voxel’ residual water artifact at > 4 ppm is unfolded by the PRIAM reconstruction into the contralateral hemisphere in the single excitation example (b).

PRIAM reconstruction of localized MRS data is feasible provided that the voxel locations to be separated have sufficiently different coil sensitivity profiles; when they are similar, the reconstructions will have increased noise. Use of higher magnetic fields and more receiver coils will allow voxels that are closer together to be separated.

This study demonstrates that PRIAM is feasible for simultaneously acquiring spectra from both hemispheres of the brain, thereby reducing scan time compared to conventional, sequential acquisitions. PRIAM may also be used to reduce artifacts from ‘out-of-voxel’ magnetization. The protocol described is suitable for the rapid measurement of bilateral hippocampal metabolites in patients with epilepsy, or other disorders of the mesial temporal lobe.

Boer, V, Klomp, D, Barker, P, Parallel Reconstruction Image Acquisition Mode (PRIAM) in Localized Brain MR Spectroscopy.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14013981.html