Analysis of D-dimer by negative-stain EM. (A) A typical image area of negatively stained D-dimer. The bar represents 100 nm. (B) The 181 class averages obtained with the ISAC algorithm.⁴³  (C) The 100 class averages obtained by k-means classification shown from the most populous class on the top left to the least populous class at the bottom right. Averages were assigned to show D-dimers in a straight conformation (green boxes) or in a bent conformation (red boxes) or were not assigned if the features were ambiguous (black boxes). The numbers in the lower left corner of each average in panels B and C indicate the number of particles in the class; the side length of the individual averages is 42.4 nm.