Denoising Ultrasound Medical Images with Selective Fusion in Wavelet Domain

Ultrasound medical imaging is undoubtedly an incontestable tool which provides the view of the internal organs of a body. The no ionizing radiation exposure property of the ultrasound medical images made it more fitting for fetus imaging. The only major snag ultrasound imaging encompasses is speckle noise that results from constructive and destructive interference thereby degrading the quality of the image. This paper submits a twofold technique to remove this multiplicative speckle noise and to bring a contrast between the object of the interest and the remaining image. First fold includes block based hard (BHT) and soft thresholding (BST) on pixels in wavelet domain where in which the original ultrasound image is divided into Non Overlapping blocks of sizes 8, 16, 32 and 64. The second fold includes restoration of the object boundaries and texture with adaptive wavelet fusion which are lost by the blurring effect caused as a result of the first fold. Fusion of wavelet coefficients of original US image and block thresholded US images assuaged to restore the degraded object. Fusion rule and wavelet decomposition level are made adaptive for each block using gradient histograms with normalized differential mean (NDF) to introduce highest level of contrast between the denoised pixels and the object pixels in the resultant image. Thus the proposed twofold methods are named as adaptive NDF block fusion with hard and soft thresholding (ANBF-HT and ANBF-ST). Visual quality through twofold processing has improved to an interesting level. Peak signal to noise ratio (PSNR), normalized cross correlation coefficient (NCC), edge strength (ES), image quality Index (IQI) and structural similarity index (SSIM), measure the quantitative quality of the twofold processing technique. Validation of the proposed method is done by comparing with anisotropic diffusion (AD), total variational filtering (TVF) and empirical mode decomposition (EMD) for enhancement of US images. The US images are provided by AMMA hospital radiology labs at Vijayawada, India.