QGS and MyoMetrix both fit an ellipsoid to these clusters to determine the midmural centerline and use asymmetric Gaussian curves to define endocardial and epicardial surfaces. ECTb employs a radial search for maximum counts to define the midmural centerline and adds 5 mm on each side of the centerline to define endocardial and epicardial surfaces. Exini heart detects the midmural centerline by using a heart shaped model that contains statistical information of the variability of LV shape, and defines endocardial and epicardial surfaces as the position corresponding to 75% of the maximal count values. Magnetic resonance (MR) imaging is considered the reference standard for quantifying LV volumes and function [ 7 ].