Robust reconstruction of B1+ maps by projection into a spherical functions space
Article first published online: 13 FEB 2013
Copyright © 2013 Wiley Periodicals, Inc.
Magnetic Resonance in Medicine
Volume 71, Issue 1, pages 394–401, January 2014
How to Cite
Sbrizzi, A., Hoogduin, H., Lagendijk, J. J., Luijten, P. and van den Berg, C. A. T. (2014), Robust reconstruction of B1+ maps by projection into a spherical functions space. Magn Reson Med, 71: 394–401. doi: 10.1002/mrm.24640
- Issue published online: 17 DEC 2013
- Article first published online: 13 FEB 2013
- Manuscript Accepted: 20 DEC 2012
- Manuscript Revised: 19 DEC 2012
- Manuscript Received: 5 JUL 2012
- B1+ mapping;
- parallel transmit;
- Helmholtz equation;
- spherical harmonics;
- radiofrequency field mapping
Several parallel transmit MRI techniques require knowledge of the transmit radiofrequency field profiles (B1+). During the past years, various methods have been developed to acquire this information. Often, these methods suffer from long measurement times and produce maps exhibiting regions with poor signal-to-noise ratio and artifacts. In this article, a model-based reconstruction procedure is introduced that improves the robustness of B1+ mapping.
Theory and Methods
The missing information from undersampled B1+ maps and the regions of poor signal to noise ratio are reconstructed through projection into the space of spherical functions that arise naturally from the solution of the Helmholtz equations in the spherical coordinate system.
As a result, B1+ data over a limited range of the field of view/volume is sufficient to reconstruct the B1+ over the full spatial domain in a fast and robust way. The same model is exploited to filter the noise of the measured maps. Results from simulations and in vivo measurements confirm the validity of the proposed method.
A spherical functions model can well approximate the magnetic fields inside the body with few basis terms. Exploiting this compression capability, B1+ maps are reconstructed in regions of unknown or corrupted values. Magn Reson Med 71:394–401, 2014. © 2013 Wiley Periodicals, Inc.