Nonlinear smoothing of MR images using approximate entropy — A local measure of signal intensity irregularity.
In: (Biennial International Conference on Information Processing in Medical Imaging). Berlin [u.a.]: Springer, 1999. 484-489 (Lect. Notes Comput. Sc. ; 1613)
Approximate entropy (ApEn) is a computable measure of sequential irregularity that is applicable to sequences of numbers of finite length. As such, it may be used to determine how random a sequence of numbers is. We exploit this property to determine the relevance of image information; to determine whether a spatial signal intensity distribution varies in a regular fashion — and is therefore likely to be an image feature or image texture, or is highly random — and likely to be noise. We present an outline of two possible methodologies for creating an ApEn-based noise filter: a modified median filter and a modified anisotropic diffusion scheme. We show that both approaches lead to effective noise reduction in MR images, with improved information-retaining properties when compared with their conventional counterparts.