1. Unbalanced SSFP for super‐resolution in MRI
- Author
-
Paul M. Matthews, Neal K. Bangerter, Peter J Lally, Wellcome Trust, and UK DRI Ltd
- Subjects
super‐ ,structured illumination microscopy ,SSFP ,computer.software_genre ,030218 nuclear medicine & medical imaging ,White matter ,03 medical and health sciences ,Magnetization ,0302 clinical medicine ,Optics ,0903 Biomedical Engineering ,Flip angle ,Voxel ,Image Processing, Computer-Assisted ,medicine ,Radiology, Nuclear Medicine and imaging ,High Resolution Imaging ,Physics ,Science & Technology ,Super-Resolution ,medicine.diagnostic_test ,Phantoms, Imaging ,business.industry ,Radiology, Nuclear Medicine & Medical Imaging ,RF power amplifier ,resolution ,Specific absorption rate ,spatial encoding ,Magnetic resonance imaging ,Steady-state free precession imaging ,Magnetic Resonance Imaging ,Nuclear Medicine & Medical Imaging ,medicine.anatomical_structure ,Artifacts ,business ,Life Sciences & Biomedicine ,computer ,030217 neurology & neurosurgery - Abstract
Purpose To achieve rapid, low specific absorption rate (SAR) super-resolution imaging by exploiting the characteristic magnetization off-resonance profile in SSFP. Theory and methods In the presented technique, low flip angle unbalanced SSFP imaging is used to acquire a series of images at a low nominal resolution that are then combined in a super-resolution strategy analogous to non-linear structured illumination microscopy. This is demonstrated in principle via Bloch simulations and synthetic phantoms, and the performance is quantified in terms of point-spread function (PSF) and SNR for gray and white matter from field strengths of 0.35T to 9.4T. A k-space reconstruction approach is proposed to account for B0 effects. This was applied to reconstruct super-resolution images from a test object at 9.4T. Results Artifact-free super-resolution images were produced after incorporating sufficient preparation time for the magnetization to approach the steady state. High-resolution images of a test object were obtained at 9.4T, in the presence of considerable B0 inhomogeneity. For gray matter, the highest achievable resolution ranges from 3% of the acquired voxel dimension at 0.35T, to 9% at 9.4T. For white matter, this corresponds to 3% and 10%, respectively. Compared to an equivalent segmented gradient echo acquisition at the optimal flip angle, with a fixed TR of 8 ms, gray matter has up to 34% of the SNR at 9.4T while using a ×10 smaller flip angle. For white matter, this corresponds to 29% with a ×11 smaller flip angle. Conclusion This approach achieves high degrees of super-resolution enhancement with minimal RF power requirements.
- Published
- 2020