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K‐space filter deconvolution and flip angle self‐calibration in 2D radial hyperpolarised 3 He lung MRI
Author(s) -
Marshall Helen,
Ajraoui Salma,
Deppe Martin H.,
ParraRobles Juan,
Wild Jim M.
Publication year - 2012
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1766
Subject(s) - deconvolution , calibration , physics , space (punctuation) , filter (signal processing) , flip angle , nuclear magnetic resonance , magnetic resonance imaging , optics , computer science , medicine , radiology , quantum mechanics , computer vision , operating system
In hyperpolarised 3 He lung MRI with constant flip angles, the transverse magnetisation decays with each RF excitation imposing a k‐space filter on the acquired data. For radial data acquired in an angularly‐sequential order, this filter causes streaking, angular shading and loss of spatial resolution in the images. The main aim of this work was to reduce the effects of the RF depletion k‐space filter in radial acquisitions. Two approaches are presented; (i) retrospective deconvolution of the k‐space filter for sequentially‐acquired data and (ii) golden angle acquisition order. Radial trajectories sample the centre of k‐space with every projection, thereby self‐tracking signal decay. The inverse of the signal decay function was used to retrospectively deconvolve RF depolarisation k‐space filter effects and the method was demonstrated in 2D radial imaging in phantoms and human lungs. A golden angle radial acquisition was shown to effectively suppress artefacts caused by the RF depletion k‐space filter. In addition, the average flip angle per slice was calculated from the signal decay and the values were found to correspond with conventional flip angle maps, providing a means of flip angle self‐calibration. Copyright © 2011 John Wiley & Sons, Ltd.