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European Journal of Echocardiography 2005 6(2):84; doi:10.1016/j.euje.2004.12.004
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Copyright © 2005, The European Society of Cardiology

Reply to Letter to the Editor

Camilla Storaa*

Karolinska Institutet, Division of Medical Engineering, Novum F60, SE-14186 Huddinge, Sweden

camilla.storaa{at}labmed.ki.se

* Tel.: +46 8 58583758; fax: +46 8 58587779.

We appreciate the interest of Dr. Koutroulis in our article.1 The Lagrangian strain definition {varepsilon}=(L–L0)/L0 Dr. Koutroulis refers to is only one of several possible one dimensional strain definitions. Another commonly used definition in echocardiography is the so called natural strain2:


Formula

The relationship between the two is {varepsilon}N=ln(1+{varepsilon}),2 hence natural strain can also be calculated from the tissue motion images.1 The complete three dimensional strain is described by the strain tensor.2 All these strain definitions are functions of the current and previous lengths of the object, thus they only give a measure of the amount of deformation and are independent of the properties of the material. They do not describe a load-elongation relationship.

As Dr. Koutroulis points out soft tissues are inhomogeneous and anisotropic, properties which would have to be taken into account if one was to model the myocardium as a material. Such material models can be linked to the above mentioned strain tensor and then give stress–strain or load-elongation relationships. Models like this are under continuous development.3,4


   References
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 References
 

  1. Storaa C., Cain P., Olstad B., Lind B., Brodin L.Å. Tissue motion imaging of the left ventricle – quantification of myocardial strain, velocity, acceleration and displacement in a single image. Eur J Echocardiogr (2004 Oct) 5(5):375–385.[Abstract/Free Full Text]
  2. D'hooge J., Heimdal A., Jamal F., Kukulski T., Bijnens B., Rademakers F., et al. Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations. Eur J Echocardiogr (2000 Sep) 1(3):154–170.[Abstract/Free Full Text]
  3. Remme E.W., Hunter P.J., Smiseth O., Stevens C., Rabben S.I., Skulstad H., et al. Development of an in vivo method for determining material properties of passive myocardium. J Biomech (2004 May) 37(5):669–678.[CrossRef][Web of Science][Medline]
  4. Bischoff J.E. Static indentation of anisotropic biomaterials using axially asymmetric indenters – a computational study. J Biomech Eng (2004 Aug) 126(4):498–505.[CrossRef][Web of Science][Medline]

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This Article
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