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Abstract:
Purpose/Introduction: K-space weighting by acquiring different numbers of averages depending on position in k-space [1,2] is a well-known and oftenused technique to avoid signal contamination due to the the unfavorable shape
of the point-spread function (PSF) in chemical shift imaging. In addition, it is well-known that this technique can improve the apparent SNR by avoiding negative signal contributions from other regions of the sample [3]. This
advantage, however, has so far barely been used in imaging, mainly because it requires averaging [4]. For high-resolution images, where averaging is anyway
necessary for SNR reasons, k-space weighted acquisition can help to improve resolution and SNR without sacrificing scan time.
Subjects and Methods: To demonstrate the SNR gain that is possible by kspace weighted acquisition, a 3D-FLASH sequence with weighting in both phase encode directions was implemented. The scheme of the radial weighting function was adjusted to yield equal resolution in the same scan time as a standard FLASH sequence with otherwise identical parameters.
Results: Figure 1 shows a comparison of PSFs of the weighted and unweighted sequences. While the width of the PSF is equal in both cases, implying equal spatial resolution, signal contributions from outside the voxel are strongly suppressed by weighted acquisition, resulting in reduced Gibbs-ringing and improved apparent SNR.
Discussion/Conclusion: For high-resolution imaging, where averaging is required for SNR-reasons, k-space weighted acquisition can help to significantly improve SNR and image quality with no extra cost in scan time.
