T1 weighted fat/water separated PROPELLER acquired with dual bandwidths

• Published in: Magnetic resonance in medicine 2018-12, Vol.80 (6), p.2501-2513
• Main Authors: Rydén, Henric, Berglund, Johan, Norbeck, Ola, Avventi, Enrico, Skare, Stefan
• Format: Article
• Language: English
• Subjects: Chemical equilibrium; dixon; Echoes; Efficiency; Image acquisition; Image quality; Inverse problems; motion correction; MRI; Noise; Organic chemistry; PROPELLER; Regularization
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.27228

Purpose To describe a fat/water separated dual receiver bandwidth (rBW) spin echo PROPELLER sequence that eliminates the dead time associated with single rBW sequences. A nonuniform noise whitening by regularization of the fat/water inverse problem is proposed, to enable dual rBW reconstructions. Methods Bipolar, flyback, and dual spin echo sequences were developed. All sequences acquire two echoes with different rBW without dead time. Chemical shift displacement was corrected by performing the fat/water separation in k‐space, prior to gridding. The proposed sequences were compared to fat saturation, and single rBW sequences, in terms of SNR and CNR efficiency, using clinically relevant acquisition parameters. The impact of motion was investigated. Results Chemical shift correction greatly improved the image quality, especially at high resolution acquired with low rBW, and also improved motion estimates. SNR efficiency of the dual spin echo sequence was up to 20% higher than the single rBW acquisition, while CNR efficiency was 50% higher for the bipolar acquisition. Noise whitening was deemed necessary for all dual rBW acquisitions, rendering high image quality with strong and homogenous fat suppression. Conclusion Dual rBW sequences eliminate the dead time present in single rBW sequences, which improves SNR efficiency. In combination with the proposed regularization, this enables highly efficient T1‐weighted PROPELLER images without chemical shift displacement.