Virtual tagging for analysing cardiac deformation

Magnetic resonance (MR) imaging has shown great promise in the assessment of cardiac anatomy and function. The most commonly used techniques for measuring cardiac deformation are MR tagging and velocity mapping methods. The quantitative analysis of these images at present, however, is time-consuming and requires considerable user interaction. The purpose of this paper is to introduce a virtual tagging method that combines the advantages of both imaging techniques. It allows easy visualization of cardiac deformation and permits a quantitative analysis of the strain at different phases of the cardiac cycle. The method used is to "float" a virtual grid above the underlying velocity data. The intersections of the grid move as a function of the velocities within each quadrilateral contained by the intersection points. This representation allows the user to clearly visualize the underlying data and the deformation of the grid. The deformation can also be used to quantify physical indices such as strain and strain rate.