Infiltrative nature of lesions is a significant feature of malignant breast lesion in ultrasound images. Characterizing infiltrative nature is crucial for the realization of computer-aided diagnosis system. In this study, the infiltrative nature is regarded as an energy that produces irregularly & considerably local variances in a 1-D signal. The local variances can be enhanced by few high octave energies in 1-D discrete periodized wavelet transform (DPWT). A test dataset of breast sonograms with the lesion contour delineated by an experienced physician & two inexperienced students are built for feature efficacy evaluation. A high individual performance result implies that the proposed feature is well correlated with radiologist's perception & closer to match those in trained physician than morphometric parameters. Experimental results also reveal that with a great performance improvement, the proposed feature is suitable for the combination with some morphometric parameters.