Intravital microscopy workstations. Mouse tumor models are observed using (A) conventional intravital microscopy or (B) MPLSM. With appropriate tracer molecules and/or engineered vectors/cells and computer-assisted image analysis, one can monitor tumor size, vessel density, vessel diameter, RBC velocity, leukocyte endothelial interaction, vascular permeability, tissue pO₂, pH, gene promoter activity, enzyme activity, and delivery of drugs, including genes. (B: Adapted, with permission, from Brown et al. 2001.)