Figure 6c. HARP analysis of short-axis tagged MR images. (a) A circular grid that contains a variable number of segments of equal size (in this case, 12) is defined by the user to represent the region of measurement within the left ventricular wall (green = subendocardial layer, red = midwall, blue = subepicardial layer). Points on the grid are then automatically tracked through all the image sections in the data set, and strain values are calculated from the trajectory of each point. (b) Calculated strain values are displayed as a color-coded map superimposed on the tagged images. (c) Strain plots show circumferential shortening in every segment and in all three layers (color coded as in a and b). The x axis represents the number of imaged phases of the cardiac cycle (20, up to a maximum of 670 msec), and the y axis is the percentage of change in circumferential shortening.