Ultrastructural analysis of neurofibrillary tangles of Alzheimer's disease using computerized digital processing.

The ultrastructure of neurofibrillary tangles of Alzheimer's disease was analyzed by computerized digital processing of electron micrographs. Processing of the electron micrographs consists of four steps: digitizing the electron micrograph, Fourier transformation, noise filtering and inverse Fourier transformation and Laplacian operation. In the present study, we have confirmed that neurofibrillary tangles are composed of a pair of helical filaments (PHF), which appear characteristically as an unbranched rigid structure. The periodicity of PHF is 78 nm on the diffractogram. The dimensions of PHF obtained by our analysis, although basically similar to those described earlier by other investigators using conventional techniques, more precisely defines its structural conformation. We have also demonstrated that the spatial relationship of two filaments appears symmetrical after two-way tilting of the specimen about the axis of rotation. Our observations emphasize the importance of digital image processing as an effective tool for structural analytical research in biology and medicine.