Quantification of myocardial strain at early systole in mouse heart: restoration of undeformed tagging grid with single-point HARP.

PURPOSE: To develop accurate strain and torsion quantification method for the assessment of myocardial contraction in mice by MRI tagging.
MATERIALS AND METHODS: Ventricular wall motion at baseline and during beta-adrenergic stimulation was assessed in mice using MRI tagging. Myocardial strain and torsion were quantified using finite element analysis method. A harmonic phase (HARP) based method was developed for the restoration of undeformed taglines for more accurate calculation of myocardial wall strain and torsion.
RESULTS: Myocardial deformation was observed at early systole (<20 msec after QRS) both at baseline and during beta-adrenergic stimulation. The HARP-based method allowed robust restoration of undeformed taglines that can be used as the reference in finite element analysis of the tagged images. Without such correction for myocardial deformation in the reference image, inaccuracy in strain quantification underestimated significant strain development at early systole in dobutamine-stimulated hearts.
CONCLUSION: The HARP-based method developed in the current study enabled automated restoration of undeformed taglines in mouse hearts, leading to more accurate calculation of myocardial wall strain and torsion during dobutamine stimulation.