Figure 6. In vivo detection of microparticle location and dynamics. (A) Overview of THG emitting randomly distributed microparticles (white arrowheads) and aggregated, likely intracellular vesicles (asterisks) detected at the border of a B16F10 tumor (d13) nearby collagen fiber-containing stroma. (B) The distribution of particle sizes determined from the cross-section of the THG signal. (C) Representative tracks of individual microparticles over 49 frames (98 min) showed subpopulations of immobilization (x, immobilized on cells or on collagen fibers), or random or directed diffusion kinetics. (D) Distribution of microparticle velocities (gray bars, 82 trajectories) relative to the distribution of velocities of individually tracked marker regions on collagen fibers (empty bars, 137 trajectories). (E) Logarithmic distribution of diffusion constant of individual trajectories from microparticles (gray bars) and second harmonic generating spots on collagen fibers (empty bars). Bars, 50µm (left image) or 5µm (right images and trajectories).