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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Languages: English
Types: Doctoral thesis
Subjects: TA
Atherosclero8is represents a major health problem in the western world. The local haemodynamics is believed to be an initiating and localizing factor in this multilactorial disease process. To fully understand this interaction it is important to obtain detailed information about the local haemodynamics in accurate models of the hnrnan vascular system. Because of the complexity of arterial geometry, in mvo velocity measurements are subject to large errors by currently available techniques. It is also difficult to construct the highly irregular arterial bifurcation model for in vitro investigations. By using a combination of two new methodologies,namely magnetic resonance angiography (MRA) and computational fluid dynamics CFD), the precise patterns of flow anticipating the onset of disease at arterial bifurcations can now, in principle, be determined. However, flow simulations based on in vzvo data directly acquired from clinical measurements have rarely been performed, due to difficulties involved in converting medical images into a data set that CFD software packages can accept. ,In this study, a computer modelling technique, which integrates dinically acquired MR angiograms, image processing and CFD, for the reconstruction of 3D blood flow patterns in realistic arterial geometry, was developed. In the procedure, human arteries are scanned non-invasively by MR angiography. With the MR angiograms, image processing and 3D reconstruction are performed and structured numerical grid is generated for the arteries scanned. Together with MR in tnvo measured velocity profiles at the boundary planes of the model, CFD simulations are undertaken. To test the capability and reliability of the whole procedure, two examples are given, of the human abdominal and right carotid bifurcations. The complete haemodynamic patterns obtained allow a full clinical understanding to be gained of individual patient behaviour. Aspects such as wall shear stress variation, secondary flow and flow separations are demonstrated. The problem of quantitative reliability of the predictions is discussed in some depth.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • 2 Literature Survey 26 2.1 Introduction ..................................... 26 2.2 Magnetic Resonance Angiography ......................... 27 2.2.1 Time-Of-Flight techniques ......................... 27 2.2.1.1 2D Time-of-Flight MBA .................... 29 2.2.1.2 3D Time-of-Flight MBA .................... 30 2.2.2 Phase-Contrast techniques ......................... 31 2.2.3 Contrast enhanced MBA ......................... 34 2.2.4 Phase-Contrast velocity measurement .................. 35 2.2.4.1 Electrocardiogram (ECG) gating methods and cine PC MRI 35 2.2.4.2 Measurement of flow rate through a vessel .......... 38 2.2.4.3 Fourier velocity encoding technique .............. 39 2.2.4.4 Rapid phase flow imaging method ............... 41 2.2.5 Image Processing in MRA ......................... 41 4.3.2 Logical registration 124 4.3.3 Error analysis of the registration methods ................ 125 4.3.4 Temporal interpolation .......................... 125
    • 6 CFD predictions cases 1: a human abdominal bifurcation 143 6.1 Introduction ..................................... 143 6.2 Model geometrical description andboundary conditions .............................. 144 6.3 CFD Predictions ..................................148 6.3.1 Velocity distribution ............................148 6.3.2 Wall Shear Stress distribution .......................154 6.3.3 Summary of the CFD predictions for the abdominal bifurcation model 158 Validations .....................................159 6.4.1 Part 1: computational error assessment .................160 6.4.1.1 Grid resolution and temporal resolution tests .........160 6.4.1.2 Comparison with different boundary conditions ........165 6.4.2 Part 2: Overall CFD simulation validation ................168 6.4.2.1 Comparison with MR measured velocity profile in the abdominalaorta .............................168 6.4.2.2 Assessment of uncertainties in the overall validation .....170 6.4.3 Summary of the validation ........................173 Conclusion .....................................174
    • 7 CFD predictions case 2: a human carotid bifurcation 175 7.1 IfltroduCtion .....................................175 7.2 Model geometrical description andboundary conditions ..............................176 7.3 CFD Predictions ..................................180 7.3.1 Velocity distribution ............................. 180 7.3.2 Wall Shear Stress distribution .......................188 7.4 Validations .....................................192 7.4.1 Part one: numerical errors .........................192 7.4.1.1 Grid resolution and temporal resolution tests .........192 7.4.1.2 Comparison between different boundary conditions ......198 7.4.2 Part two: influence of smoothing parameters in geometry reconstructionon the CFD predictions ........................202 7.4.3 Part three: comparison with MR measured velocity profiles in the commoncarotid artery .............................203 7.5 Conclusion .....................................207 4.1 Sample images of the Cine PC scan: (a) phase (velocity) image; and (b) magnitudeimage.....................................120
    • 5.1 Control Volume Notation .............................131
    • 6.1 Geometrical description of the abdominal bifurcation model. (a) anterior view; (b) posterior view; (c) left view; (d) arbitrary view angle ............145
    • 1. Long Q, Xu XY, Collins MW, Griffith TM and Bourne M (1998) The Combination of Magnetic Resonance Angiography and Computational Fluid Dynamics: a critical review. Critical reviews in biomedical engineering, 26(4):227-276
    • 2. Long Q, Xu XY, Collins MW, Bourne M and Griffith TM (1998) Magnetic Resonance Image Processmg and Structured Grid Generation of a Human Abdominal Bifurcation. Computer Methods and Programs in Biomedicine, 56:249-259
    • 3. Long Q, Xu XY, Collins MW, Griffith TM and Bourne M (1997) Some fluid dynamics aspects of the aortic bifurcation using magnetic resonance imaging and computational fluid dynamics. Internal Medicine, 5(1):33-39
    • 4. Xu XY, Long Q, Collins MW, Griffith TM and Bourne M (1999) 3D Reconstruction of the flow in humAn arteries. Proc. of IMechE, J. of Eng. in Med. (in press).
    • 5. Long Q, Xu XY, Collins MW, Griffith TM and Bourne M (1999) Simulation of flow in human arterial bifurcations using a combination of CFD and MRI techniques. Haemodynamics of Arterial Organs - Comparison of Computational Predictions with in Vivo and in Vitro Data, Eds: Collins MW and Xu XY, WIT Press (in press).
    • 1. Long Q, Xu XY and Collins MW (1998) 3D Visualization of blood flows in arterial organs: A novel development of computational methods using MR or Ultrasound data Proc. 8th International Symposium on Flow Visualization, Sorrento Italy.
    • 2. Long Q, Xu XY, Collins MW, Stanton A, Thom SA and Hughes AD (1998) Reproducibiity analysis of 3D geometrical reconstruction of a human arterial bifurcation Proc. Medical Image Understanding and Analysis '98, Leeds University, pp 21-24
    • 3. Long Q, Xu XY, Collins MW, Griffith TM and Bourne M (1997) Generation of CFD Velocity Boundary Condition from Cine MR Phase-Contrast Images. Proc. Medical Image Underatand*ng and Analysis '97, Univ. of Ozford1 pp 117-120.
    • 4. Collins MW and Long Q (1997) Three-dimensional numerical simulation of oscillatory flow in blood vessel branches. Proc. Workshop'97, Biomechanical Modeling E NumerwaS Simulation, Prague, Sept. 25-U, pp 7-19
    • 5. Q. Long, X.Y. Xu, M.W. Collins (1996) Generation of Structure of the Aortic Bifurcation From Magnetic Resonance Angiograin. Simulation Modelling in Bioengineering, Eds: M Cerrolaza et aS, Comput. Mech. Pub., pp217-226
    • [23] Quinn SF., Demlow TA., Hahn RW. et a! (1993) Femoral MR-angiography versus conventional angiography - preimirniry results, Radiology, 189: ppl8l-l84
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    • [25) Cellermi M, Konze A, Sottili P, Peilicano G, DalPozzo G (1997) MRA techniques: state of the art Rivuta L)* Neurr,radsologia 10:82-84
    • [26] Blatter DD, Parker DL and R.obison RO (1991) Cerebral MR angiography with multiple overlapping thin slab acquisition, Radiology, 179: pp805-8ll
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