Dynamic tracking in interventional MRI using wavelet-encoded gradient-echosequences

This work describes a newly developed magnetic resonance imaging (MRI) data -acquisition strategy which replaces the standard Fourier phase-encoding wi th the spatially localized coefficients of wavelet-encoding and offers a ne w technique for image guidance when combined with a dynamic tracking algori thm. By using this new technique, only a specific fraction of the entire ra w data set needs to be updated and reconstructed to visualize the movement of an interventional device during an MR guided procedure. The combination of wavelet-encoding and a dynamic tracking algorithm was implemented in two -dimensional and three-dimensional gradient-echo sequences on a 0.2-T open C-arm-shaped MR system (Siemens, Erlangen Germany) and tested in phantom an d in vitro experiments, When applying the wavelet-encoding direction parall el to the movement of a straight interventional device, only those spatiall y localized wavelet-coefficients mainly affected by the interventional devi ce are updated. This led to potential increases of the image frame rate by a factor of up to seven.