Quantification of transmural differences in myocardial function with MRI tagging

Many cardiac diseases cause transmural differences in myofiber function. With the Magnetic Resonance Imaging Tagging technique a grid of magnetic tags was attached to the heart. Using a model of cardiac mechanics the motion of these tags was analyzed to deduct the transmural gradient or myofiber shortening. In normal, young healthy subjects (n=9), the transmural difference in myofiber shortening varies little, about ±4% (sd) of mean shortening. In patients with aortic stenosis subendocardial function is at risk. In a group of such patients (n=5) fiber shortening in the subendocardial layers was found to be decreased by 23±20% relative to the subepicardial layers. This finding indicates that a model of cardiac mechanics can be used as a tool to convert MRI-tagging motion data to clinically useful information on a transmural gradient in contractile function. Presently, no other methods are available to detect such transmural gradient noninvasively.