Lateral Inverse Filtering of Ultrasonic B-Scan Images

Abstract

The formation of ultrasonic B-scan images using parallel beams may be modelled as a lateral, one-dimensional convolution of the beam profile and an unknown but wanted reflection coefficient. Lateral inverse filtering, or deconvolution, might therefore be used to improve the image quality. Two different deconvolution techniques are applied to both an image of a tissue mimicking phantom and a human liver. An enhancement of the resolution (defined as the reciprocal of the half-width of the image of a point reflector) of about 1.4 is achieved. This is in good agreement with the previously derived formula R = , which relates the signal-to-noise ratio, SNR, to the resolution enhancement, R. However, each method also creates artifacts, and despite the slight resolution enhancement, the deconvolved liver images do not exhibit more information nor are they more appealing. So it is felt that the computational effort is wasted. This failure is not a fault of the special deconvolution techniques tried here, but rather caused by the logarithmic dependence of R on SNR and by the noise level, which is largely due to macro- and microscopic inhomogeneities of the tissue and cannot be made arbitrarily small.