Overview of Mass Cytometry Methodology and Data Analysis.Procedure: Top, cells isolated from patient or control samples are labeled with metal tagged antibodies, whose atomic masses are read by the CyTOF mass cytometer. Below, a spectrum of atomic masses of lanthanide metals used to label antibodies for mass cytometry.Analysis: Top, multiple signaling molecules can be measured simultaneously and compared in patient versus control sample cell populations. Middle, SPADE (Spanning tree Progression of Density normalized Events) analysis illustrates signaling across multiple cell populations basally and in response to stimulation with TNFα (tumor necrosis factor-α). Bottom, viSNE (Visualization of t-distributed Stochastic Neighbor Embedding algorithm) plots identifying the persistence of CD34+ stem/progenitor cells in the peripheral blood of a myelofibrosis patient prior to (left) and on treatment (right) with ruxolitinib.