Fig. 4.

Schematic diagram of the distribution of particles within the boundaries of the axon at time t. The solid line represents the medial axis of the axon, as described by the cubic spline interpolation. The dashed lines represent the boundaries of the axon region which extend to a distance on d* either side of the medial axis. The black rectangular bounding boxes represent some particles distributed within the axon region as defined by the axon constraint. The bold black rectangular bounding box represents the particle in this example with the maximum observation likelihood, which corresponds to the location of the neurofilament. By rejecting those particles that lie outside the boundaries of the axon and that do not conform to the orientation of the axon, we reduce the number of particles required to locate the neurofilament.