Phase-insensitive homomorphic image processing for speckle reduction

Abstract

Speckle appears in all conventional ultrasound images and is caused by the use of a coherent transducer. Speckle is an undesirable property as it can mask small but perhaps diagnostically significant features. Speckle noise can be reduced using a phase-insensitive imaging technique to cancel the linear phase relationship between elements. However, with current devices this is hard to achieve because of the large memory and high sampling rate requirements for the 64 or more multiple channels used. To address the problems above, a hybrid method is introduced that combines the phase-insensitive technique with a phase-sensitive speckle reduction method. Several phase-correlated subimages (2 or 4) are formed using classical imaging techniques. Then nonlinear homomorphic processing is applied to destroy the phase relationship between these images. The homomorphic, phase-insensitive, and hybrid nonlinear processing method is developed and examined in this paper. Experiments with synthetic and real ultrasound imagery show that the proposed method improves the signal-to-noise ratio in both lesion and cyst areas and preserves edge clarity. [Work supported by NSF.]