There is one options available for the myocardium detection: the Epi/Endo active model. This segmentation technique is based on the active model technique in 3D (active surface). Initially, a heart model is fitted to the averaged data. It is used for initializing the active surfaces in each gate, which are then fitted to the data. The procedure is performed for the Epi and Endo surfaces. The capture below illustrates the result of outlining obtained with the Stair case icon 
OFF.
The uptake is sampled in the resulting heart models by polar sampling as described previously.