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Reply: REPLY: velocities in aneurysms, which may cause mislocations of the zero velocity points. Therefore, we suggest that it should be e applaud the advanced and multidirectional studies per- verified that their vortex core lines are located in the center of 1 2 Wformed by Wetzel et al and Meckel et al. We agree with vortex flows in aneurysms. This verification would guarantee Meckel et al, who showed that aneurysms with an irregular the usefulness of the tool integrating the algorithm to auto- shape or a high aspect ratio may have complex and unstable flow. matically identify vortex core lines in aneurysms and to avoid In our study, we differentiated vortex core lines from vortex the interobserver differences. We hope that the tool helps to cores. We identified vortex cores as thin streamline bundles with clarify the role of the vortical flow pattern in aneurysm behav- minimum velocities by progressively decreasing a threshold to vis- ior in future studies. ualize flow streamlines with velocities under the threshold in aneurysms. In extremely low velocity thresholds, a vortex core REFERENCES was exhibited as a line. In our study, we did not include such lines 1. Wetzel S, Meckel S, Frydrychowicz A, et al. In vivo assessment and visu- into vortex cores, because we could not definitely discriminate the alization of intracranial arterial hemodynamics with flow-sensitized lines from irregular streamlines which were usually visualized in 4D MR imaging at 3T. AJNR Am J Neuroradiol 2007;28:433–38 Medline aneurysms via 4D flow MR imaging. In our study, the velocity- 2. Meckel S, Stalder AF, Santini F, et al. In vivo visualization and analysis encoding (VENC) for 4D flow MR imaging was set to 40–60 cm/s of 3-D hemodynamics in cerebral aneurysms with flow sensitized 4-D to correctly extract low-velocity vectors in aneurysms. We verified MR imaging at 3 T. Neuroradiology 2008;50:473–84 CrossRef Medline that the thin streamline bundle was a vortex core by showing that 3. Futami K, Uno T, Misaki K, et al. Identification of vortex cores in cerebral aneurysms on 4D flow MRI. AJNR Am J Neuroradiol the bundle passed through the center of vortical flow vectors in 2019;40:2111–16 CrossRef Medline the aneurysmal dome. 4. Sujudi D, Haimes R. Identification of swirling flow in 3-D vector Meckel et al showed a vortex core line using an algorithm to fields. In: Proceedings of the 12th Computational Fluid Dynamics identify the points on the face where reduced velocity is zero and Conference, San Diego, California; June 19–22, 1995; https://doi.org/ to connect these distinct points. However, the locations of vortex 10.2514/6.1995-1715 CrossRef core lines can vary between algorithms. In 4 of 5 aneurysms K. Futami examined in their study, the VENC for 4D flow MR imaging was Department of Neurosurgery 90 cm/s to detect high-velocity flow components. This VENC Hokuriku Central Hospital value can lead to errors in the extraction of flow vectors with low Toyama, Japan K. Misaki M. Nakada Department of Neurosurgery http://dx.doi.org/10.3174/ajnr.A6474 Kanazawa University School of Medicine Ishikawa, Japan AJNR Am J Neuroradiol 41:E27 May 2020 www.ajnr.org E27 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Neuroradiology American Journal of Neuroradiology

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Publisher
American Journal of Neuroradiology
Copyright
© 2020 by American Journal of Neuroradiology
ISSN
0195-6108
eISSN
1936-959X
DOI
10.3174/ajnr.A6474
Publisher site
See Article on Publisher Site

Abstract

REPLY: velocities in aneurysms, which may cause mislocations of the zero velocity points. Therefore, we suggest that it should be e applaud the advanced and multidirectional studies per- verified that their vortex core lines are located in the center of 1 2 Wformed by Wetzel et al and Meckel et al. We agree with vortex flows in aneurysms. This verification would guarantee Meckel et al, who showed that aneurysms with an irregular the usefulness of the tool integrating the algorithm to auto- shape or a high aspect ratio may have complex and unstable flow. matically identify vortex core lines in aneurysms and to avoid In our study, we differentiated vortex core lines from vortex the interobserver differences. We hope that the tool helps to cores. We identified vortex cores as thin streamline bundles with clarify the role of the vortical flow pattern in aneurysm behav- minimum velocities by progressively decreasing a threshold to vis- ior in future studies. ualize flow streamlines with velocities under the threshold in aneurysms. In extremely low velocity thresholds, a vortex core REFERENCES was exhibited as a line. In our study, we did not include such lines 1. Wetzel S, Meckel S, Frydrychowicz A, et al. In vivo assessment and visu- into vortex cores, because we could not definitely discriminate the alization of intracranial arterial hemodynamics with flow-sensitized lines from irregular streamlines which were usually visualized in 4D MR imaging at 3T. AJNR Am J Neuroradiol 2007;28:433–38 Medline aneurysms via 4D flow MR imaging. In our study, the velocity- 2. Meckel S, Stalder AF, Santini F, et al. In vivo visualization and analysis encoding (VENC) for 4D flow MR imaging was set to 40–60 cm/s of 3-D hemodynamics in cerebral aneurysms with flow sensitized 4-D to correctly extract low-velocity vectors in aneurysms. We verified MR imaging at 3 T. Neuroradiology 2008;50:473–84 CrossRef Medline that the thin streamline bundle was a vortex core by showing that 3. Futami K, Uno T, Misaki K, et al. Identification of vortex cores in cerebral aneurysms on 4D flow MRI. AJNR Am J Neuroradiol the bundle passed through the center of vortical flow vectors in 2019;40:2111–16 CrossRef Medline the aneurysmal dome. 4. Sujudi D, Haimes R. Identification of swirling flow in 3-D vector Meckel et al showed a vortex core line using an algorithm to fields. In: Proceedings of the 12th Computational Fluid Dynamics identify the points on the face where reduced velocity is zero and Conference, San Diego, California; June 19–22, 1995; https://doi.org/ to connect these distinct points. However, the locations of vortex 10.2514/6.1995-1715 CrossRef core lines can vary between algorithms. In 4 of 5 aneurysms K. Futami examined in their study, the VENC for 4D flow MR imaging was Department of Neurosurgery 90 cm/s to detect high-velocity flow components. This VENC Hokuriku Central Hospital value can lead to errors in the extraction of flow vectors with low Toyama, Japan K. Misaki M. Nakada Department of Neurosurgery http://dx.doi.org/10.3174/ajnr.A6474 Kanazawa University School of Medicine Ishikawa, Japan AJNR Am J Neuroradiol 41:E27 May 2020 www.ajnr.org E27

Journal

American Journal of Neuroradiology – American Journal of Neuroradiology

Published: May 1, 2020

References

  • In vivo assessment and visualization of intracranial arterial hemodynamics with flow-sensitized 4D MR imaging at 3T
    Wetzel