The shifted radial reordering for intermediate TE imaging in 3D long echo train acquisition

Introduction Use of nonselective pulses and modulated flip angles (aka SPACE, [2, 3, 4]) in refocusing pulses improves the sampling efficiency in 3D turbo spin echo imaging. Two flexible reordering schemes, the linear mode and the radial mode, have been proposed [1] to circumvent some intrinsic limitations of the rectangular kspace sampling grid (e.g., allowing for flexible k-space coverage) in segmented 3D imaging. The proposed radial reordering is good for ultra-short or ultra-long TE imaging, where the data from the first echo or last echo are put into the k-space center. However, it does not support intermediate TE values, which are useful in some body or orthopedic imaging applications. Compared to the linear reordering (Fig.1b), the radial reordering in intermediate TE imaging is sometimes preferred since it gives well defined contrast weighting, reduces intensity fluctuation at the k-space center as well as image blurring during Partial Fourier (PF) imaging. We propose here a method to support intermediate TE imaging using radial sampling. Methods In this abstract, the typical radial reordering is called the centric mode. The new radial reordering scheme will be called the shifted mode (see Fig. 1c, 1d). In 3D long echo train imaging, let L = the turbo factor and represents the echo train length, M = the echo number at the k-space center and M < L/2. In the shifted radial reordering, each echo train represents one view going through the center region of the radial k-space. When the M echo in the echo train is defined as the k-space center, there are L/2 echoes on one side of the view, and M echoes along the other side. The actual echo train length in one view is shortened from L to L/2+M. L/2-M echoes will be missing in each view. When the azimuth angle goes from 0 to π during sampling, the missing echoes may be reconstructed using PF reconstruction. The effective PF factor is given by ( ) L M L f PF + = 2 / ;