title: Radial strain gradient across the normal myocardial wall in open-chest pigs measured with doppler strain rate imaging.
abstract: BACKGROUND
  One of the reasons for the large variation in radial strain measured with Doppler strain rate imaging in normal myocardium might be the different strain length (SL) used during analyses. The aim of this study was to evaluate the effect of different SL settings on strain recordings and the method's ability to detect transmural radial strain gradients.
  
  
  METHODS
  In 8 anesthetized pigs (mean weight 54 kg) epicardial echocardiography was performed. Strain analysis was carried out by defining the wall as a 1-, 2-, 3-, and 4-layer structure with suitable regions of interest. Peak ejection strain was measured with SL settings of 2 to 14 mm.
  
  
  RESULTS
  The systolic (ejection) strain showed large variation with SL. Sampling in one layer gave no significant reduction in strain for increasing SL. The strain in the subepicardial layer was low and decreased when the wall was divided into several layers (15.9 +/- 4.8% [2 layers]-2.1 +/- 2.4% [4 layers]; both measurements with SL = 4 mm). The method could separate 4 layers with SL of 4 mm or less, 3 layers with SL of 6 mm or less, and 2 layers with SL of 8 mm or less.
  
  
  CONCLUSIONS
  When measuring radial strain in the myocardial wall the SL must be low to evaluate transmural strain gradients. With correct settings of SL and region of interest, strain in 4 layers can be distinguished. As a rule of thumb the SL should be set to approximately half the systolic thickness of the wall or half the wall layer.
authors.affiliation: Institute of Medicine, Department of Surgical Sciences, University of Bergen, Haukeland University Hospital, Bergen, Norway. Knut.Matre@med.uib.no
authors.forename: Knut
authors.initials: K
authors.lastname: Matre
authors.forename: Tord
authors.initials: T
authors.lastname: Fanneløp
authors.forename: Geir Olav
authors.initials: GO
authors.lastname: Dahle
authors.forename: Andreas
authors.initials: A
authors.lastname: Heimdal
authors.forename: Ketil
authors.initials: K
authors.lastname: Grong
mesh_terms: D000818:Animals; D016880:Anisotropy; D015150:Echocardiography, Doppler / Q000379:methods*; D004548:Elasticity; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D013552:Swine; D016276:Ventricular Function; D016277:Ventricular Function, Left / Q000502:physiology*