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Ghost-Free Spin-Echo Echo Planar Imaging Method for Diffusion Weighted Images using Adaptive RF Pulses

(0,0,0) as a reference. Images were also acquired with the conventional SE-DW-EPI sequence as a comparison and the diffusion values were calculated using a homemade software. When acquiring conventional SE-DW-EPI, and 8 NEX images were acquired to match the total acquisition time with the proposed method. Discussions Figure 2 shows the DWIs acquired using the conventional SE-DW-EPI (left) and the proposed method (right). The intensity of the images is amplified for displaying purposes. As shown in the images, It is clear that the proposed method produces ghost-free images with no loss in signal strength. This is because the N/2 ghosts are generated because of the phase difference in odd and even lines of the k-space data. Since a perfect phase error correction is very difficult, we rather suggested that the images to be acquired separately with even N/2 ghost and odd N/2 ghost. Each image contains N/2 ghost on the other side of the main image but the other side of the image containing the N/2 ghost is cut off during the concatenation, producing a ghost-free full image. Note that the signal strength from the conventional method does not look much better even though it is averaged twice the number of averages used for the proposed method. Calculated diffusion matrix images are shown in fig.3. The matrix calculated from the images acquired by the proposed method (top) seems clearer than that from the conventional one (bottom). In case of tensor calculation, it is more important to reduce N/2ghost because the artifact can significantly alter the final tracking results. A further analysis of the diffusion images and calculated valued need still to be done. Conclusions We acquired ghost-free diffusion weighted images using alternating RF selection pulses applied in the phase encoding direction. When used in combination with other methods which can reduce ghost-related artifacts, acquisition time can be further reduced and we can acquire images with better SNR which are free of N/2 ghosts.