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Improving Assessments of Hemodynamics and Vascular Disease
Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. (CMR)ORCID-id: 0000-0001-9184-9234
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Blood vessels are more than simple pipes, passively enabling blood to pass through them. Their form and function are dynamic, changing with both aging and disease. This process involves a feedback loop wherein changes to the shape of a blood vessel affect the hemodynamics, causing yet more structural adaptation. This feedback loop is driven in part by the hemodynamic forces generated by the blood flow, and the distribution and strength of these forces appear to play a role in the initiation, progression, severity, and the outcome of vascular diseases.

Magnetic Resonance Imaging (MRI) offers a unique platform for investigating both the form and function of the vascular system. The form of the vascular system can be examined using MR-based angiography, to generate detailed geometric analyses, or through quantitative techniques for measuring the composition of the vessel wall and atherosclerotic plaques. To complement these analyses, 4D Flow MRI can be used to quantify the functional aspect of the vascular system, by generating a full time-resolved three-dimensional velocity field that represents the blood flow.

This thesis aims to develop and evaluate new methods for assessing vascular disease using novel hemodynamic markers generated from 4D Flow MRI and quantitative MRI data towards the larger goal of a more comprehensive non-invasive examination oriented towards vascular disease. In Paper I, we developed and evaluated techniques to quantify flow stasis in abdominal aortic aneurysms to measure this under-explored aspect of aneurysmal hemodynamics. In Paper II, the distribution and intensity of turbulence in the aorta was quantified in both younger and older men to understand how aging changes this aspect of hemodynamics. A method to quantify the stresses generated by turbulence that act on the vessel wall was developed and evaluated using simulated flow data in Paper III, and in Paper V this method was utilized to examine the wall stresses of the carotid artery. The hemodynamics of vascular disease cannot be uncoupled from the anatomical changes the vessel wall undergoes, and therefore Paper IV developed and evaluated a semi-automatic method for quantifying several aspects of vessel wall composition. These developments, taken together, help generate more valuable information from imaging data, and can be pooled together with other methods to form a more comprehensive non-invasive examination for vascular disease.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2019. , s. 64
Serie
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1675
Nationell ämneskategori
Medicinsk bildbehandling Biomedicinsk laboratorievetenskap/teknologi
Identifikatorer
URN: urn:nbn:se:liu:diva-156311DOI: 10.3384/diss.diva-156311ISBN: 9789176850985 (tryckt)OAI: oai:DiVA.org:liu-156311DiVA, id: diva2:1304518
Disputation
2019-05-31, Hugo Theorell, Norra Entrén, Campus US, Linköping, 13:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Vetenskapsrådet, 2013-06077Vetenskapsrådet, 2017-03857Region Östergötland, LIO-752951Tillgänglig från: 2019-04-17 Skapad: 2019-04-12 Senast uppdaterad: 2019-04-24Bibliografiskt granskad
Delarbeten
1. Visualizing and quantifying flow stasis in abdominal aortic aneurysms in men using 4D flow MRI
Öppna denna publikation i ny flik eller fönster >>Visualizing and quantifying flow stasis in abdominal aortic aneurysms in men using 4D flow MRI
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2019 (Engelska)Ingår i: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 57, s. 103-110Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Purpose: To examine methods for visualizing and quantifying flow stasis in abdominal aortic aneurysms (AAA) using 4D Flow MRI. Methods: Three methods were investigated: conventional volumetric residence time (VRT), mean velocity analysis (MVA), and particle travel distance analysis (TDA). First, ideal 4D Flow MRI data was generated using numerical simulations and used as a platform to explore the effects of noise and background phase-offset errors, both of which are common 4D Flow MRI artifacts. Error-free results were compared to noise or offset affected results using linear regression. Subsequently, 4D Flow MRI data for thirteen (13) subjects with AAA was acquired and used to compare the stasis quantification methods against conventional flow visualization. Results: VRT (R-2 = 0.69) was more sensitive to noise than MVA (R-2 = 0.98) and TDA (R-2 = 0.99) at typical noncontrast signal-to-noise ratio levels (SNR = 20). VRT (R-2 = 0.14) was more sensitive to background phase-offsets than MVA (R-2 = 0.99) and TDA (R-2 = 0.96) when considering a 95% effective background phase-offset correction. Qualitatively, TDA outperformed MVA (Wilcoxon p amp;lt; 0.005, mean score improvement 1.6/5), and had good agreement (median score 4/5) with flow visualizations. Conclusion: Flow stasis can be quantitatively assessed using 4D Flow MRI. While conventional residence time calculations fail due to error accumulation as a result of imperfect measured velocity fields, methods that do not require lengthy particle tracking perform better. MVA and TDA are less sensitive to measurement errors, and TDA generates results most similar to those obtained using conventional flow visualization.

Ort, förlag, år, upplaga, sidor
ELSEVIER SCIENCE INC, 2019
Nyckelord
Abdominal aortic aneurysm; Hemodynamics; 4D flow MRI; Flow stasis
Nationell ämneskategori
Medicinsk laboratorie- och mätteknik
Identifikatorer
urn:nbn:se:liu:diva-154524 (URN)10.1016/j.mri.2018.11.003 (DOI)000458096100012 ()30445146 (PubMedID)
Tillgänglig från: 2019-02-20 Skapad: 2019-02-20 Senast uppdaterad: 2019-04-17
2. Age-Related Vascular Changes Affect Turbulence in Aortic Blood Flow
Öppna denna publikation i ny flik eller fönster >>Age-Related Vascular Changes Affect Turbulence in Aortic Blood Flow
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2018 (Engelska)Ingår i: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, artikel-id 36Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Turbulent blood flow is implicated in the pathogenesis of several aortic diseases but the extent and degree of turbulent blood flow in the normal aorta is unknown. We aimed to quantify the extent and degree of turbulece in the normal aorta and to assess whether age impacts the degree of turbulence. 22 young normal males (23.7 +/- 3.0 y.o.) and 20 old normal males (70.9 +/- 3.5 y.o.) were examined using four dimensional flow magnetic resonance imaging (4D Flow MRI) to quantify the turbulent kinetic energy (TKE), a measure of the intensity of turbulence, in the aorta. All healthy subjects developed turbulent flow in the aorta, with total TKE of 3-19 mJ. The overall degree of turbulence in the entire aorta was similar between the groups, although the old subjects had about 73% more total TKE in the ascending aorta compared to the young subjects (young = 3.7 +/- 1.8 mJ, old = 6.4 +/- 2.4 mJ, p amp;lt; 0.001). This increase in ascending aorta TKE in old subjects was associated with age-related dilation of the ascending aorta which increases the volume available for turbulence development. Conversely, age-related dilation of the descending and abdominal aorta decreased the average flow velocity and suppressed the development of turbulence. In conclusion, turbulent blood flow develops in the aorta of normal subjects and is impacted by age-related geometric changes. Non-invasive assessment enables the determination of normal levels of turbulent flow in the aorta which is a prerequisite for understanding the role of turbulence in the pathophysiology of cardiovascular disease.

Ort, förlag, år, upplaga, sidor
FRONTIERS MEDIA SA, 2018
Nyckelord
turbulent kinetic energy (TKE); turbulent blood flow; aortic blood flow; aortic dilation; normal values; 4D flow MRI; phase contrast MRI
Nationell ämneskategori
Fysiologi
Identifikatorer
urn:nbn:se:liu:diva-145129 (URN)10.3389/fphys.2018.00036 (DOI)000423400000001 ()29422871 (PubMedID)
Anmärkning

Funding Agencies|Swedish Research Council [2013-6077, 2014-6191]; Swedish Heart and Lung foundation [20140398]; Kangwon National University [D1001179-01-01]; Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education [2016R1A6A3A03006337]

Tillgänglig från: 2018-02-19 Skapad: 2018-02-19 Senast uppdaterad: 2019-04-17
3. Assessment of Turbulent Flow Effects on the Vessel Wall Using Four-Dimensional Flow MRI
Öppna denna publikation i ny flik eller fönster >>Assessment of Turbulent Flow Effects on the Vessel Wall Using Four-Dimensional Flow MRI
2017 (Engelska)Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 77, nr 6, s. 2310-2319Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Purpose: To explore the use of MR-estimated turbulence quantities for the assessment of turbulent flow effects on the vessel wall. Methods: Numerical velocity data for two patient-derived models was obtained using computational fluid dynamics (CFD) for two physiological flow rates. The four-dimensional (4D) Flow MRI measurements were simulated at three different spatial resolutions and used to investigate the estimation of turbulent wall shear stress (tWSS) using the intravoxel standard deviation (IVSD) of velocity and turbulent kinetic energy (TKE) estimated near the vessel wall. Results: Accurate estimation of tWSS using the IVSD is limited by the spatial resolution achievable with 4D Flow MRI. TKE, estimated near the wall, has a strong linear relationship to the tWSS (mean R(2=)0.84). Near-wall TKE estimates from MR simulations have good agreement to CFD-derived ground truth (mean R-2=0.90). Maps of near-wall TKE have strong visual correspondence to tWSS. Conclusion: Near-wall estimation of TKE permits assessment of relative maps of tWSS, but direct estimation of tWSS is challenging due to limitations in spatial resolution. Assessment of tWSS and near-wall TKE may open new avenues for analysis of different pathologies. (C) 2016 International Society for Magnetic Resonance in Medicine

Ort, förlag, år, upplaga, sidor
WILEY, 2017
Nyckelord
phase contrast magnetic resonance imaging; wall shear stress; turbulence; turbulent kinetic energy; aorta
Nationell ämneskategori
Medicinsk bildbehandling
Identifikatorer
urn:nbn:se:liu:diva-138232 (URN)10.1002/mrm.26308 (DOI)000401270900022 ()27350049 (PubMedID)
Anmärkning

Funding Agencies|Swedish Research Council; National Supercomputer Centre [SNIC2014-11-22]

Tillgänglig från: 2017-06-14 Skapad: 2017-06-14 Senast uppdaterad: 2019-04-17

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