Biomedical Modelling with Clinical Applications

1. Biomedical Modelling with Clinical Applications Su Yi | 苏易

4. From an engineering perspective… Design- centric

5. From a clinical perspective… Patient- centric

7. An example in dealing with heart failure Epidemic of chronic heart failure among survivors of heart attack

8. LV remodelling: the process in which the heart alters its size, shape & configuration after a heart attack Serial assessment & quantitation of LV remodelling facilitates surveillance of heart failure progression tailoring of appropriate treatment & monitoring of efficacy reduce cost What happens after an heart attack?

9. How is LV remodelling being assessed? • Ejection Fraction (EF), i.e. change in LV volume • Qualitative or semi-quantitative descriptors of shape, e.g. sphericity index (SI) and conicity index (CI) • Dimension, e.g. change in LV diameter, wall thickness – image-based • Twisting, e.g. tagged-MRI, speckle tracking echocardiography – image-based • Ventricular wall stiffness (σ/ε) – FEM-based

10. LGE confirms LV apical infarct How is LV remodelling being assessed? • Cardiac magnetic resonance (CMR) imaging • LV structure and function, e.g. LV dimensions, LV volumes, etc • Infarct size and extent – late gadolinium enhancement (LGE) • Fails to exploit full range of quantitative multi-dimensional MRI data

11. 2D images 3D model 4D spatial-temporal model Our idea… • To develop new indices to quantitate LV remodelling using a computational geometry approach • Extract 3D/4D information • Provide localised patient-specific details • Apply rigorous engineering and physiological principles to derive cardiac indices which are robust and scientifically valid

12. Our approach… • What kind of clinical inference can we make from the model?

13. The aim of the surface-fitting process is to compute an extended quadric of the form which approximates the local geometry in the vicinity of a point p on a mesh. • The local curvedness (or RMS curvature) is then given by where Approximating local shape of LV

14. Extracting physical properties • Local 3D radius (R) • Local wall thickness (T) - equivalent to solving a ray-triangle intersection of a ray with the epicardial surface • Local wall stress ()

15. Is 3D method better than 2D image-based methods? • 10 normal subjects

16. t1 r1 t2 r2 Why is a 3D method better than 2D image-based methods?

17. Regional curvedness • 10 control; 10 diseased

18. Regional Wall Stress and Thickening High wall stress, especially at apex Very little wall thickening despite high wall stress

19. Validation against LGE late gadolinium enhancement representing myocardial scaring/fibrosis

20. Surgical Ventricular Restoration • 40 patients; pre- and post-SVR Before SVR 4 months after SVR

21. Comparison to other methods

22. What are the implications? • Potential to replace delayed contrast hyperenhancement MRI • Reduce scanning time/cost by at least 25% • Avoid the need to inject Gadolinium which might result in complication in some patients • Reduce patient trauma

23. What are the current limitations? • Current approach does not exploit full 4D information; finite difference between end-diastole and end-systole phase • Partitioning of endocardial surface according to medical nomenclature assumes rigid rotation and linear vertical compression; not realistic • Assumption of uniform pressure loading in LV chamber

24. What’s needed to bring this to the next level? • Clinical trial & testbedding • 20 normal • 30 diseased over time (at least 1 year) • age-matched • gender-matched

25. Acceptance by clinicians • Medical Journals • Zhong L, Su Y, Yeo SY, Tan RS, Ghista DN, Kassab G. Three-dimensional curvedness and wall stress assessment in dilated cardiomyopathy using magnetic resonance imaging. Am J Physiol Heart Circ Physiol, 296: H573-H584, 2009. • Yeo SY, Zhong L, Su Y, Tan RS, Ghista DN. A curvature-based approach for left ventricular shape analysis from cardiac magnetic resonance imaging. Med Biol Eng Comput,47(3): 313-322, 2009. • Invited Book Chapter • Zhong L, Tan RS, Su Y, Yeo SY, Ghista DN, Kassab G. Noninvasive Assessment of Left Ventricular Remodeling: Geometry, Wall Stress and Function, in Computational Cardiovascular Mechanics: Modeling and Applications in Heart Failure, Julius Guccione and Mark Radcliff, Ed. • Medical Conferences • L. Zhong, Y. Su, S. Y. Yeo, D. Ghista, R. S. Tan. Three-dimensional left ventricular regional shape and wall stress alterations after surgical ventricular restoration, accepted for oral presentation at the 11th World Congress on Medical Physics and Biomedical Engineering, September 7-12, 2009 in Munich, Germany. • Yeo SY, Zhong L, Su Y, Tan RS, Ghista DN. Analysis of left ventricular surface deformation during isovolumic contraction. Conf Proc IEEE Eng Biol Soc 2007;1:787-790. (EI, PubMed) • Zhong L, Yeo SY, Su Y, Le TT, Tan RS, Ghista DN. Regional assessment of left ventricular surface shape from magnetic resonance imaging. Conf Proc IEEE Eng Biol Soc 2007;1:884-887. (EI, PubMed) • Yeo SY, Tan RS, Chai GB, Ghista DN. Variation of left ventricular surface shape during the cardiac cycle. The 3rd IASTED International Conference on Biomechanics, BioMech 2005. Benidorm, 7-9 Sep 2005.

26. Some concluding thoughts… • Near confluence point of computational and clinical practitioners • Need appropriate structure to facilitate communications • Novelty vs Impact • Ease-of-use is key

27. Thank You