@article{BrueningGoubergritsHepptetal., author = {Br{\"u}ning, Jan and Goubergrits, Leonid and Heppt, Werner and Zachow, Stefan and Hildebrandt, Thomas}, title = {Numerical Analysis of Nasal Breathing - A Pilot Study}, series = {Facial Plastic Surgery}, volume = {33}, journal = {Facial Plastic Surgery}, number = {4}, doi = {doi:10.1055/s-0037-1603789}, pages = {388 -- 395}, abstract = {Background: Currently, there is no fully sufficient way to differentiate between symptomatic and normal nasal breathing. Using the nose's total resistance is disputed as a valid means to objectify nasal airflow, and the need for a more comprehensive diagnostic method is increasing. This work's aim was to test a novel approach considering intranasal wall shear stress as well as static pressure maps obtained by computational fluid dynamics (CFD). Methods: X-ray computed tomography (CT) scan data of six symptom-free subjects and seven symptomatic patients were used. Patient-specific geometries of the nasal cavity were segmented from these data sets. Inspiratory and expiratory steady airflow simulations were performed using CFD. Calculated static pressures and wall shear stresses (WSS) were mapped onto a common template of the nasal septum, allowing for comparison of these parameters between the two patient groups. Results: Significant differences in wall shear stress distributions during the inspiratory phase could be identified between the two groups, whereas no differences were found for the expiratory phase. It is assumed that one essential feature of normal nasal breathing probably consists in distinctively different intranasal flow fields for inspiration and expiration. This is in accordance with previous investigations. Conclusion: The proposed method seems to be a promising tool for developing a new kind of patient-specific assessment of nasal breathing. However, more studies and a greater case number of data with an expanded focus, would be ideal.}, language = {en} } @article{BrueningHildebrandtHepptetal., author = {Br{\"u}ning, Jan and Hildebrandt, Thomas and Heppt, Werner and Schmidt, Nora and Lamecker, Hans and Szengel, Angelika and Amiridze, Natalja and Ramm, Heiko and Bindernagel, Matthias and Zachow, Stefan and Goubergrits, Leonid}, title = {Characterization of the Airflow within an Average Geometry of the Healthy Human Nasal Cavity}, series = {Scientific Reports}, volume = {3755}, journal = {Scientific Reports}, number = {10}, doi = {10.1038/s41598-020-60755-3}, abstract = {This study's objective was the generation of a standardized geometry of the healthy nasal cavity. An average geometry of the healthy nasal cavity was generated using a statistical shape model based on 25 symptom-free subjects. Airflow within the average geometry and these geometries was calculated using fluid simulations. Integral measures of the nasal resistance, wall shear stresses (WSS) and velocities were calculated as well as cross-sectional areas (CSA). Furthermore, individual WSS and static pressure distributions were mapped onto the average geometry. The average geometry featured an overall more regular shape that resulted in less resistance, reduced wall shear stresses and velocities compared to the median of the 25 geometries. Spatial distributions of WSS and pressure of average geometry agreed well compared to the average distributions of all individual geometries. The minimal CSA of the average geometry was larger than the median of all individual geometries (83.4 vs. 74.7 mm²). The airflow observed within the average geometry of the healthy nasal cavity did not equal the average airflow of the individual geometries. While differences observed for integral measures were notable, the calculated values for the average geometry lay within the distributions of the individual parameters. Spatially resolved parameters differed less prominently.}, language = {en} } @article{GoubergritsHellmeierBrueningetal., author = {Goubergrits, Leonid and Hellmeier, Florian and Bruening, Jan Joris and Spuler, Andreas and Hege, Hans-Christian and Voss, Samuel and Janiga, G{\´a}bor and Saalfeld, Sylvia and Beuing, Oliver and Berg, Philipp}, title = {Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH): Uncertainty Quantification of Geometric Rupture Risk Parameters}, series = {BioMedical Engineering OnLine}, volume = {18}, journal = {BioMedical Engineering OnLine}, number = {35}, doi = {10.1186/s12938-019-0657-y}, abstract = {Background Geometric parameters have been proposed for prediction of cerebral aneurysm rupture risk. Predicting the rupture risk for incidentally detected unruptured aneurysms could help clinicians in their treatment decision. However, assessment of geometric parameters depends on several factors, including the spatial resolution of the imaging modality used and the chosen reconstruction procedure. The aim of this study was to investigate the uncertainty of a variety of previously proposed geometric parameters for rupture risk assessment, caused by variability of reconstruction procedures. Materials 26 research groups provided segmentations and surface reconstructions of five cerebral aneurysms as part of the Multiple Aneurysms AnaTomy CHallenge (MATCH) 2018. 40 dimensional and non-dimensional geometric parameters, describing aneurysm size, neck size, and irregularity of aneurysm shape, were computed. The medians as well as the absolute and relative uncertainties of the parameters were calculated. Additionally, linear regression analysis was performed on the absolute uncertainties and the median parameter values. Results A large variability of relative uncertainties in the range between 3.9 and 179.8\% was found. Linear regression analysis indicates that some parameters capture similar geometric aspects. The lowest uncertainties < 6\% were found for the non-dimensional parameters isoperimetric ratio, convexity ratio, and ellipticity index. Uncertainty of 2D and 3D size parameters was significantly higher than uncertainty of 1D parameters. The most extreme uncertainties > 80\% were found for some curvature parameters. Conclusions Uncertainty analysis is essential on the road to clinical translation and use of rupture risk prediction models. Uncertainty quantification of geometric rupture risk parameters provided by this study may help support development of future rupture risk prediction models.}, language = {en} } @article{GoubergritsKertzscherAffeldetal.2008, author = {Goubergrits, Leonid and Kertzscher, Ulrich and Affeld, Klaus and Petz, Christoph and Stalling, Detlev}, title = {Numerical Dye Washout Method as a Tool for Characterizing the Heart Valve Flow}, series = {ASAIO Journal}, volume = {54(1)}, journal = {ASAIO Journal}, doi = {10.1097/MAT.0b013e31815c5e38}, pages = {50 -- 57}, year = {2008}, language = {en} } @article{GoubergritsKertzscherSchoenebergetal.2008, author = {Goubergrits, Leonid and Kertzscher, Ulrich and Sch{\"o}neberg, Bastian and Wellnhofer, Ernst and Petz, Christoph}, title = {CFD analysis in an anatomically realistic coronary artery model based on non-invasive 3D imaging}, series = {Int. J. Cardiovasc. Imaging}, volume = {24(4)}, journal = {Int. J. Cardiovasc. Imaging}, doi = {10.1007/s10554-007-9275-z}, pages = {411 -- 421}, year = {2008}, language = {en} } @article{GoubergritsOsmanMevertetal., author = {Goubergrits, Leonid and Osman, Jan and Mevert, Ricardo and Kertzscher, Ulrich and P{\"o}thkow, Kai and Hege, Hans-Christian}, title = {Turbulence in blood damage modeling}, series = {The International Journal of Artificial Organs}, volume = {39}, journal = {The International Journal of Artificial Organs}, number = {4}, doi = {10.5301/ijao.5000476}, pages = {147 -- 210}, abstract = {Purpose: To account for the impact of turbulence in blood damage modeling, a novel approach based on the generation of instantaneous flow fields from RANS simulations is proposed. Methods: Turbulent flow in a bileaflet mechanical heart valve was simulated using RANS-based (SST k-ω) flow solver using FLUENT 14.5. The calculated Reynolds shear stress (RSS) field is transformed into a set of divergence-free random vector fields representing turbulent velocity fluctuations using procedural noise functions. To consider the random path of the blood cells, instantaneous flow fields were computed for each time step by summation of RSS-based divergence-free random and mean velocity fields. Using those instantaneous flow fields, instantaneous pathlines and corresponding point-wise instantaneous shear stresses were calculated. For a comparison, averaged pathlines based on mean velocity field and respective viscous shear stresses together with RSS values were calculated. Finally, the blood damage index (hemolysis) was integrated along the averaged and instantaneous pathlines using a power law approach and then compared. Results: Using RSS in blood damage modeling without a correction factor overestimates damaging stress and thus the blood damage (hemolysis). Blood damage histograms based on both presented approaches differ. Conclusions: A novel approach to calculate blood damage without using RSS as a damaging parameter is established. The results of our numerical experiment support the hypothesis that the use of RSS as a damaging parameter should be avoided.}, language = {en} } @inproceedings{GoubergritsPoethkePetzetal.2008, author = {Goubergrits, Leonid and P{\"o}thke, Jens and Petz, Christoph and Hege, Hans-Christian and Spuler, Andreas and Kertzscher, Ulrich}, title = {3D Bildgebung von zerebralen Aneurysmen}, series = {Bildverarbeitung f{\"u}r die Medizin}, booktitle = {Bildverarbeitung f{\"u}r die Medizin}, doi = {10.1007/978-3-540-78640-5_31}, pages = {153 -- 157}, year = {2008}, language = {en} } @article{GoubergritsSchallerKertzscheretal., author = {Goubergrits, Leonid and Schaller, Jens and Kertzscher, Ulrich and Petz, Christoph and Hege, Hans-Christian and Spuler, Andreas}, title = {Reproducibility of Image-Based Analysis of Cerebral Aneurysm Geometry and Hemodynamics: An In-Vitro Study of Magnetic Resonance Imaging, Computed Tomography, and Three-Dimensional Rotational Angiography}, series = {Journal of Neurological Surgery, Part A: Central European Neurosurgery}, volume = {74}, journal = {Journal of Neurological Surgery, Part A: Central European Neurosurgery}, number = {5}, doi = {10.1055/s-0033-1342937}, pages = {294 -- 302}, language = {en} } @article{GoubergritsSchallerKertzscheretal.2012, author = {Goubergrits, Leonid and Schaller, Jens and Kertzscher, Ulrich and van den Bruck, Nils and P{\"o}thkow, Kai and Petz, Christoph and Hege, Hans-Christian and Spuler, Andreas}, title = {Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms}, series = {J. R. Soc. Interface}, volume = {9}, journal = {J. R. Soc. Interface}, number = {69}, doi = {10.1098/rsif.2011.0490}, pages = {677 -- 688}, year = {2012}, language = {en} } @article{GoubergritsSpulerSchalleretal.2014, author = {Goubergrits, Leonid and Spuler, Andreas and Schaller, Jens and Wiegmann, Nils and Berthe, Andre and Hege, Hans-Christian and Affeld, Klaus and Kertzscher, Ulrich}, title = {In vitro study of hemodynamic treatment improvement: Hunterian ligation of a fenestrated basilar artery aneurysm after coiling}, series = {The International Journal of Artificial Organs}, volume = {37}, journal = {The International Journal of Artificial Organs}, number = {4}, doi = {10.5301/ijao.5000314}, pages = {325 -- 335}, year = {2014}, abstract = {Hunterian ligation affecting hemodynamics in vessels was proposed to avoid rebleeding in a case of a fenestrated basilar artery aneurysm after incomplete coil occlusion. We studied the hemodynamics in vitro to predict the hemodynamic changes near the aneurysm remnant caused by Hunterian ligation. A transparent model was fabricated based on three-dimensional rotational angiography imaging. Arteries were segmented and reconstructed. Pulsatile flow in the artery segments near the partially occluded (coiled) aneurysm was investigated by means of particle image velocimetry. The hemodynamic situation was investigated before and after Hunterian ligation of either the left or the right vertebral artery (LVA/RVA). Since post-ligation flow rate in the basilar artery was unknown, reduced and retained flow rates were simulated for both ligation options. Flow in the RVA and in the corresponding fenestra vessel is characterized by a vortex at the vertebrobasilar junction, whereas the LVA exhibits undisturbed laminar flow. Both options (RVA or LVA ligation) cause a significant flow reduction near the aneurysm remnant with a retained flow rate. The impact of RVA ligation is, however, significantly higher. This in vitro case study shows that flow reduction near the aneurysm remnant can be achieved by Hunterian ligation and that this effect depends largely on the selection of the ligated vessel. Thus the ability of the proposed in vitro pipe-line to improve hemodynamic impact of the proposed therapy was successfully proved.}, language = {en} }