tailieunhanh - EURASIP Journal on Applied Signal Processing 2003:5, 470–478 c 2003 Hindawi Publishing

EURASIP Journal on Applied Signal Processing 2003:5, 470–478 c 2003 Hindawi Publishing Corporation Speckle Suppression in Ultrasonic Images Based on Undecimated Wavelets Fabrizio Argenti Dipartimento di Elettronica e Telecomunicazioni, Universit` di Firenze, Via di Santa Marta 3, 50139 Firenze, Italy a Email: argenti@ Gionatan Torricelli Dipartimento di Elettronica e Telecomunicazioni, Universit` di Firenze, Via di Santa Marta, 3, 50139 Firenze, Italy a Email: torricelli@ Received 11 February 2002 and in revised form 29 October 2002 An original method to denoise ultrasonic images affected by speckle is presented. Speckle is modeled as a signal-dependent noise corrupting the image. Noise reduction is approached as a Wiener-like filtering. | EURASIP Journal on Applied Signal Processing 2003 5 470-478 2003 Hindawi Publishing Corporation Speckle Suppression in Ultrasonic Images Based on Undecimated Wavelets Fabrizio Argenti Dipartimento di Elettronica e Telecomunicazioni Universita di Firenze Via di Santa Marta 3 50139 Firenze Italy Email argenti@ Gionatan Torricelli Dipartimento di Elettronica e Telecomunicazioni Universita di Firenze Via di Santa Marta 3 50139 Firenze Italy Email torricelli@ Received 11 February 2002 and in revised form 29 October 2002 An original method to denoise ultrasonic images affected by speckle is presented. Speckle is modeled as a signal-dependent noise corrupting the image. Noise reduction is approached as a Wiener-like filtering performed in a shift-invariant wavelet domain by means of an adaptive rescaling of the coefficients of an undecimated octave decomposition. The scaling factor of each coefficient is calculated from local statistics of the degraded image the parameters of the noise model and the wavelet filters. Experimental results demonstrate that excellent background smoothing as well as preservation of edge sharpness and fine details can be obtained. Keywords and phrases ultrasound image denoising speckle filtering linear minimum mean square error filtering undecimated discrete wavelet transform. 1. INTRODUCTION Since the introduction of first coherent imaging systems speckle noise has been widely studied. Speckle makes a homogeneous object to assume a granular appearance and consequently the contrast of the image is drastically reduced. The presence of a speckle pattern in a coherently formed image is due to the received backscatter signal from un-resolvable particles constituting the inspected mean. Particular attention has been reserved to speckle noise in ultrasonic images since the degradation in the acquired image implies strong uncertainties in the detection of pathologies performed by an expert human observer. The texture of .