Frank J, Chiu W, Degn L. The characterization of structural variations within a crystal field. Ultramicroscopy 26:345-360, 1988.
The technique of correlation averaging is refined by the use of multivariate statistical analysis and classification. The refined method can deal with the presence of structural variations within a crystal field. A low-dose image of a crotoxin crystal embedded in ice is used to demonstrate that crystallographic structural parameters characterizing the different areas of such a crystal with varying structure can be extracted rigorously and reproducibly.