title: K-space filter deconvolution and flip angle self-calibration in 2D radial hyperpolarised 3He lung MRI.
abstract: 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.
authors.affiliation: Unit of Academic Radiology, University of Sheffield, Floor C, Royal Hallamshire Hospital, Glossop Road, Sheffield, UK, S10 2JF. H.Marshall@sheffield.ac.uk
authors.forename: Helen
authors.initials: H
authors.lastname: Marshall
authors.forename: Salma
authors.initials: S
authors.lastname: Ajraoui
authors.forename: Martin H
authors.initials: MH
authors.lastname: Deppe
authors.forename: Juan
authors.initials: J
authors.lastname: Parra-Robles
authors.forename: Jim M
authors.initials: JM
authors.lastname: Wild
mesh_terms: D002138:Calibration; D003198:Computer Simulation; D006371:Helium; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007554:Isotopes; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves
chemical_list: D007554:Isotopes; D006371:Helium