Four-dimensional B-spline based motion analysis of tagged MR images:introduction and in vivo validation

Abstract

In MRI tagging, magnetic tags - spatially encoded magneticsaturation planes - are created within tissues acting astemporary markers. Their deformation pattern provides usefulqualitative and quantitative information about the functionalproperties of underlying tissue and allows non-invasive analysisof mechanical function. The measured displacement at a given tagpoint contains only unidirectional information; in order to trackthe full 3D motion, these data have to be combined withinformation from other orthogonal tag sets over all time frames.Here, we provide a method to describe the motion of the heartusing a four-dimensional tensor product of B-splines. Invivo validation of this tracking algorithm is performed usingdifferent tagging sets on the same heart. Using the validationresults, the appropriate control point density was determined fornormal cardiac motion tracking. Since our motion fields areparametric and based on an image plane based Cartesiancoordinate system, trajectories or other derived values (velocity,acceleration, strains...) can be calculated for any desiredpoint within the volume spanned by the control points. Thismethod does not rely on specific chamber geometry, so the motionof any tagged structure can be tracked. Examples of displacementand strain analysis for both ventricles are also presented.