GLORIA

GEOMAR Library Ocean Research Information Access

X

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Online Resource
    Online Resource
    Virtual stenting of intracranial aneurysms: A pilot study for the prediction of treatment success based on hemodynamic simulations
    SAGE Publications ; 2018
    In:  The International Journal of Artificial Organs Vol. 41, No. 11 ( 2018-11), p. 698-705
    Details
    In: The International Journal of Artificial Organs, SAGE Publications, Vol. 41, No. 11 ( 2018-11), p. 698-705
    Abstract: Endovascular treatment of intracranial aneurysms using flow-diverting devices has revolutionized the treatment of large and complex lesions due to its minimally invasive nature and potential clinical outcomes. However, incomplete or delayed occlusion and persistent intracranial aneurysm growth are still an issue for up to one-third of the patients. We evaluated two patients with intracranial aneurysm located at the internal carotid artery who were treated with flow-diverting devices and had opposite outcomes. Both patients presented with similar aneurysms and were treated with the same device, but after a 1-year follow-up, one case presented with complete occlusion (Case 1) and the other required further treatment (Case 2). To reproduce the interventions, virtual stents were deployed and blood flow simulations were carried out using the respective patient-specific geometries. Afterward, hemodynamic metrics such as aneurysmal inflow reduction, wall shear stresses, oscillatory shear, and inflow concentration indices were quantified. The hemodynamic simulations reveal that for both cases, the neck inflow was clearly reduced due to the therapy (Case 1: 19%, Case 2: 35%). In addition, relevant hemodynamic parameters such as time-averaged wall shear stress (Case 1: 35.6%, Case 2: 57%) and oscillatory shear (Case 1: 33.1%, Case 2: 26.7%) were decreased considerably. However, although stronger relative reductions occurred in the unsuccessful case, the absolute flow values in the successful case were approximately halved. The findings demonstrate that a high relative effect of endovascular devices is not necessarily associated with the desired treatment outcome. Instead, it appears that a successful intracranial aneurysm therapy requires a certain patient-specific inflow threshold.
    Type of Medium: Online Resource
    ISSN: 0391-3988 , 1724-6040
    URL: Article
    DOI: 10.1177/0391398818775521
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2018
    detail.hit.zdb_id: 1474999-3
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 2
    Online Resource
    Online Resource
    4D-CT angiography versus 3D-rotational angiography as the imaging modality for computational fluid dynamics of cerebral aneurysms
    BMJ ; 2020
    In:  Journal of NeuroInterventional Surgery Vol. 12, No. 6 ( 2020-06), p. 626-630
    Details
    In: Journal of NeuroInterventional Surgery, BMJ, Vol. 12, No. 6 ( 2020-06), p. 626-630
    Abstract: Computational fluid dynamics (CFD) can provide valuable information regarding intracranial hemodynamics. Patient-specific models can be segmented from various imaging modalities, which may influence the geometric output and thus hemodynamic results. This study aims to compare CFD results from aneurysm models segmented from three-dimensional rotational angiography (3D-RA) versus novel four-dimensional CT angiography (4D-CTA). Methods Fourteen patients with 16 cerebral aneurysms underwent novel 4D-CTA followed by 3D-RA. Endoluminal geometries were segmented from each modality using an identical workflow, blinded to the other modality, to produce 28 'original' models. Each was then minimally edited a second time to match length of branches, producing 28 additional 'matched' models. CFD simulations were performed using estimated flow rates for 'original' models (representing real-world experience) and patient-specific flow rates from 4D-CTA for 'matched' models (to control for influence of modality alone). Results Overall, geometric and hemodynamic results were consistent between models segmented from 3D-RA and 4D-CTA, with correlations improving after matching to control for operator-introduced variability. Despite smaller 4D-CTA parent artery diameters (3.49±0.97 mm vs 3.78±0.92 mm for 3D-RA; p=0.005) and sac volumes (157 (37–750 mm 3 ) vs 173 (53–770 mm 3 ) for 3D-RA; p=0.0002), sac averages of time-averaged wall shear stress (TAWSS), oscillatory shear (OSI), and high frequency fluctuations (measured by spectral power index, SPI) were well correlated between 3D-RA and 4D-CTA 'matched' control models (TAWSS, R 2 =0.91; OSI, R 2 =0.79; SPI, R 2 =0.90). Conclusions Our study shows that CFD performed using 4D-CTA models produces reliable geometric and hemodynamic information in the intracranial circulation. 4D-CTA may be considered as a follow-up imaging tool for hemodynamic assessment of cerebral aneurysms.
    Type of Medium: Online Resource
    ISSN: 1759-8478 , 1759-8486
    URL: Article
    DOI: 10.1136/neurintsurg-2019-015389
    Language: English
    Publisher: BMJ
    Publication Date: 2020
    detail.hit.zdb_id: 2506028-4
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 3
    Online Resource
    Online Resource
    How patient-specific do internal carotid artery inflow rates need to be for computational fluid dynamics of cerebral aneurysms?
    BMJ ; 2021
    In:  Journal of NeuroInterventional Surgery Vol. 13, No. 5 ( 2021-05), p. 459-464
    Details
    In: Journal of NeuroInterventional Surgery, BMJ, Vol. 13, No. 5 ( 2021-05), p. 459-464
    Abstract: Computational fluid dynamics (CFD) has become a popular tool for studying ‘patient-specific’ blood flow dynamics in cerebral aneurysms; however, rarely are the inflow boundary conditions patient-specific. We aimed to test the impact of widespread reliance on generalized inflow rates. Methods Internal carotid artery (ICA) flow rates were measured via 2D cine phase-contrast MRI for 24 patients scheduled for endovascular therapy of an ICA aneurysm. CFD models were constructed from 3D rotational angiography, and pulsatile inflow rates imposed as measured by MRI or estimated using an average older-adult ICA flow waveform shape scaled by a cycle-average flow rate (Q avg ) derived from the patient’s ICA cross-sectional area via an assumed inlet velocity. Results There was good overall qualitative agreement in the magnitudes and spatial distributions of time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and spectral power index (SPI) using generalized versus patient-specific inflows. Sac-averaged quantities showed moderate to good correlations: R 2 =0.54 (TAWSS), 0.80 (OSI), and 0.68 (SPI). Using patient-specific Q avg to scale the generalized waveform shape resulted in near-perfect agreement for TAWSS, and reduced bias, but not scatter, for SPI. Patient-specific waveform had an impact only on OSI correlations, which improved to R 2 =0.93. Conclusions Aneurysm CFD demonstrates the ability to stratify cases by nominal hemodynamic ‘risk’ factors when employing an age- and vascular-territory-specific recipe for generalized inflow rates. Q avg has a greater influence than waveform shape, suggesting some improvement could be achieved by including measurement of patient-specific Q avg into aneurysm imaging protocols.
    Type of Medium: Online Resource
    ISSN: 1759-8478 , 1759-8486
    URL: Article
    DOI: 10.1136/neurintsurg-2020-015993
    Language: English
    Publisher: BMJ
    Publication Date: 2021
    detail.hit.zdb_id: 2506028-4
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 4
    Online Resource
    Online Resource
    Robust cerebrovascular blood velocity and flow rate estimation from 4D‐ CTA
    Wiley ; 2019
    In:  Medical Physics Vol. 46, No. 5 ( 2019-05), p. 2126-2136
    Details
    In: Medical Physics, Wiley, Vol. 46, No. 5 ( 2019-05), p. 2126-2136
    Abstract: Blood velocity and flow rate information may be helpful for a wide variety of applications, but it often requires separate acquisitions. The dynamic information combined with the high spatial resolution of four‐dimensional computed tomography angiography (4D‐CTA) offers the possibility to quantify blood flow simultaneous to vascular anatomy. Methods A 4D‐ CTA clinical protocol with a novel dedicated postprocessing were validated in vitro in a patient‐specific model, and tested in a pilot study of six patients. Blood flow was assessed in both internal carotid ( ICA s) and vertebral ( VA s) arteries by analyzing spatial displacement of contrast agent in the form of time‐intensity curves ( TIC s). Unlike previous approaches, it does not require any a priori assumptions about TIC shape, but rather computes mean velocity and flow rates from the spatial displacement of the TIC s along the automatically segmented vessels. Results In vitro experiments showed good agreement between 4D‐ CTA and flowmeter measurements under steady and pulsatile flow conditions. In vivo measurements exhibited large interpatient variability of the TIC shapes, from which blood flow rates could nevertheless be successfully measured in all patients and investigated vessels. On average, measured flow rates were 3.2 ± 0.7 ml/s (in ICA s) and 1.3 ± 0.8 ml/s (in VA s) consistent with previous reference standards. Contrary to our novel approach, which considered the full TIC shape, application of previous time‐to‐peak analyses based on idealized TIC shapes showed limited reliability. Conclusions We demonstrate the high potential of 4D‐ CTA for assessing blood velocity and flow rate in addition to anatomical evaluation. The wide variety of TIC shapes encountered in vivo highlights the importance of an adaptive TIC analysis as proposed in the present work.
    Type of Medium: Online Resource
    ISSN: 0094-2405 , 2473-4209
    URL: Issue
    URL: Article
    DOI: 10.1002/mp.2019.46.issue-5
    DOI: 10.1002/mp.13454
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 1466421-5
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
  • 5
    Online Resource
    Online Resource
    Towards the Clinical utility of CFD for assessment of intracranial aneurysm rupture – a systematic review and novel parameter-ranking tool
    BMJ ; 2019
    In:  Journal of NeuroInterventional Surgery Vol. 11, No. 2 ( 2019-02), p. 153-158
    Details
    In: Journal of NeuroInterventional Surgery, BMJ, Vol. 11, No. 2 ( 2019-02), p. 153-158
    Abstract: Intracranial aneurysms (IAs) are vascular dilations on cerebral vessels that affect between 1%–5% of the general population, and can cause life-threatening intracranial hemorrhage when ruptured. Computational fluid dynamics (CFD) has emerged as a promising tool to study IAs in recent years, particularly for rupture risk assessment. However, despite dozens of studies, CFD is still far from clinical use due to large variations and frequent contradictions in hemodynamic results between studies. Purpose To identify key gaps in the field of CFD for the study of IA rupture, and to devise a novel tool to rank parameters based on potential clinical utility. Methods A Pubmed search identified 231 CFD studies for IAs. Forty-six studies fit our inclusion criteria, with a total of 2791 aneurysms. For included studies, study type, boundary conditions, solver resolutions, parameter definitions, geometric and hemodynamic parameters used, and results found were recorded. Data synthesis Aspect ratio, aneurysm size, low wall shear stress area, average wall shear stress, and size ratio were the parameters that correlate most strongly with IA rupture. Limitations Significant differences in parameter definitions, solver spatial and temporal resolutions, number of cycles between studies as well as frequently missing information such as inlet flow rates were identified. A greater emphasis on prospective studies is also needed. Conclusions Our recommendations will help increase standardization and bridge the gaps in the CFD community, and expedite the process of making CFD clinically useful in guiding the treatment of IAs.
    Type of Medium: Online Resource
    ISSN: 1759-8478 , 1759-8486
    URL: Article
    URL: Article
    DOI: 10.1136/neurintsurg-2018-014246
    DOI: 10.1136/neurintsurg-2018-014246.supp1
    Language: English
    Publisher: BMJ
    Publication Date: 2019
    detail.hit.zdb_id: 2506028-4
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...