Water Fat Separation with Undersampled TSE BLADE Based on Three Point Dixon

Introduction In the three-point Dixon water fat separation method, one in-phase echo and two out-of-phase echoes are sampled in Cartesian k-space trajectory conventionally [1][2]. The Cartesian sampling is sensitive to motions, such as from pulsation and flow, which cause artifacts degrading the image quality. To address this problem, a non Cartesian sampling method, TSE BLADE three-point Dixon, is proposed in another abstract. This technique acquires one in-phase image and two out-of-phase images with two consecutive TSE BLADE sequences. Before the computation of the water-fat separation, the images are reconstructed by regridding methods traditionally [3], which require a high enough sampling rate and thus long scanning time to overcome streaking artifacts. The present work demonstrates that the integration of a total variation (TV) regularized iterative reconstruction of each image and water-fat separation calculation with undersampled BLADE k-space trajectory will reduce the scanning time, suppress streaking artifacts while maintaining a high quality of water-fat separation. Meanwhile, the proposed reconstruction method will keep the benefits of BLADE sampling, which is much less sensitive to motions. Methods Sequence: A normal TSE BLADE sequence (Fig. 1A) is used to acquire the in-phase image, a double echo TSE BLADE sequence (Fig. 1B) with equal time shiftτ from spin echo time is designed to generate the two out-of-phase images. This design ensures that gradient delays and eddy current effects will have the same impact on all acquired images. The reconstruction consists of a 2D TV regularized iterative reconstruction to work out in-phase and out-of-phase images, which is shown in the optimization problem by means of equation (1) [4][5], and followed by a water-fat separation calculation based on phase unwrapping [1]. Fig. 2 indicates the BLADE k-space trajectories with different coverage of 100% (23 blades), 82.6% (19 blades, undersampling rate=1/0.826=1.2) and 52.2% (12 blades, undersampling rate=1.9) with 18 phase encoding lines on each blade, respectively.