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. 2017 Jul 13;7:5330. doi: 10.1038/s41598-017-04676-8

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Processing of motion estimates for physiological signal monitoring. From the 4 different velocity-encoded echoes (4 flow echoes), 4 different directions of motion are measured using the Butterfly navigators and are plotted in terms of image pixels in (a). Each color represents a different channel from a 32-channel cardiac coil receiver. In (b), these estimates are rotated to the conventional right/left (R/L), anterior/posterior (A/P) and superior/inferior (S/I) directions. In (c), a low-pass filter tuned with a cut-off frequency based on the recorded cardiac rate is used to remove the cardiac signal and noise. In (d), a high-pass filter is applied to remove the low-frequency drifting that is partially attributed to the contrast administration. In (e), a coil-clustering algorithm is used to extract the dominate motion. Afterwards, the motion estimates can be directly used to compute soft-gating weights (f) or further processed for respiratory-resolved imaging (g). For respiratory-resolved imaging, the respiratory trigger points can be located and used to determine respiratory phases. Soft-gating weights based on residual patient motion from changing respiratory depth or bulk patient motion can then be computed.