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Abstract:
Purpose/Introduction: It is well known that k-space weighted
averaging has the potential to improve SNR and image quality [1] as compared to conventional averaging, but it requires sophisticated sequence modifications. Here, we show that part of its advantages can also be realized by retrospective filtering of an image acquired with
increased spatial resolution.
Subjects and Methods: Phantom images were acquired at 3 T, using a standard gradient echo sequence. A conventional dataset with two averages was compared to a single repetition of a higher resolution scan, which was k-space filtered with a Hanning-function in all three dimensions. The filter function was designed to finally yield exactly
the same spatial resolution (given by the width of the PSF) and the same experiment duration as the twice averaged conventional image. Additional experiments were performed at 14.1 T on an isolated mouse brain and at 9.4 T on the brain of a human subject.
Results: Figure 1 shows the reconstructed images of a resolution phantom. Although both images have equal spatial resolution and require the same time, the filtered image has an increased mean SNR by 41 . Filter functions and PSFs of both scans are shown above. The equal width of the PSFs at the voxel edges as well as the zoomed images of the grid demonstrate the equal spatial resolutions of both
scans. Figure 2 illustrates the SNR gain on the high resolution images of a mouse brain.
Discussion/Conclusion: Similar to acquisition weighted imaging, this retrospective alternative makes it possible to improve SNR by favorably shaping the PSF. Although not the entire SNR gain of the acquisition weighted technique can be recovered, it has the advantage of not requiring a specialized pulse sequence. In addition, it can also
be applied on the read direction, even for non-averaged images (Fig. 3), and allows adjusting the spatial resolution after acquisition.
