Tracing by means of the light rare earths (REs), particularly La and Ce, is a state-of-the-art method used to track deoxidation products during the steelmakingprocess. Traced heterogeneous multiphase inclusions are analyzed usingscanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS)to perform a 2D characterization. The sequential chemical extraction technique isimplemented for a 3D investigation to determine traced particles’actual sizes andshapes. The automated SEM/EDS measurement must be optimized since REoxides appear brighter in the backscattered electron images due to their highatomic numbers. Therefore, two grayscales are implemented for the detection ofRE-containing multiphase inclusions. Within this technique, individual RE-tracedheterogeneous nonmetallic inclusions (NMIs) are counted as separate particles.Thus, the measured NMIs must be recombined, which is achieved using a self-developed MATLAB tool. The extracted particles are also analyzed by automatedand manual SEM/EDS measurements to determine the 3D morphologies andsizes of traced NMIs