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Erschienen in:
01.10.2014 | Research Article
Spatial phase encoding exploiting the Bloch–Siegert shift effect
Erschienen in: Magnetic Resonance Materials in Physics, Biology and Medicine | Ausgabe 5/2014
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Objective
The present work introduces an alternative to the conventional \(B_{0}\)-gradient spatial phase encoding technique. By applying far off-resonant radiofrequency (RF) pulses, a spatially dependent phase shift is introduced to the on-resonant transverse magnetization. This so-called Bloch–Siegert (BS) phase shift has been recently used for \(B_{1}^{ + }\)-mapping. The current work presents the theoretical background for the BS spatial encoding technique (BS-SET) using RF-gradients.
Materials and methods
Since the BS-gradient leads to nonlinear encoding, an adapted reconstruction method was developed to obtain undistorted images. To replace conventional phase encoding gradients, BS-SET was implemented in a two-dimensional (2D) spin echo sequence on a 0.5 T portable MR scanner.
Results
A 2D spin echo (SE) measurement imaged along a single dimension using the BS-SET was compared to a conventional SE 2D measurement. The proposed reconstruction method yielded undistorted images.
Conclusions
BS-gradients were demonstrated as a feasible option for spatial phase encoding. Furthermore, undistorted BS-SET images could be obtained using the proposed reconstruction method.