Power spectrum equalization for ultrasonic image restoration.

A method of image restoration for ultrasonic B-scan images has been proposed that need no a priori knowledge on the PSF (point spread function) of the imaging system and is feasible for in vivo applications. The entire system's response, including the interposed medium and possible transducer defects, is estimated from the degraded image itself with a few simple operations. The ultrasonic image is restored based only on a knowledge of the estimated PSF and on the spectral characteristics of the resultant echo signal. The proposed method does not modify the phase relations between echoes from multiple scatterers since the restoration filter is phaseless and the display operation does not involve nonlinear detection. The effectiveness of the restoration filter was tested on simulated ultrasonic images in the absence and in the presence of interposed tissue. Then the filter was tested on a phantom made of scatterers randomly distributed in nonattenuating gel with and without an interposed medium whose attenuation linearly increases with frequency. A good correspondence between simulations and experimental results was found: both tests show an exceptional improvement of image resolution.

A piece-wise spatial invariant model of ultrasonic image formation.

A model of ultrasonic image formation has been developed for an electronically focused linear-array transducer. An analytical expression for the point-spread function of the image degradation process is obtained. It consists of two terms: one accounts for the electromechanical properties of the transducer; the other describes the diffraction phenomena associated with the wave propagation. To reduce the computational complexity in image restoration, a piecewise-invariant form for the point-spread function has been suggested. Experimental results prove the validity of the model and the feasibility of the reconstruction process with a few shift-invariant filters.

On-line two-dimensional evaluation of ultrasonic integrated backscatter.

We describe an apparatus for the on-line evaluation of integrated backscatter from areas of tissue. The equipment is fully integrated into a B-mode ultrasonic system; there are therefore no new operating procedures to be learned. It provides a simultaneous display of conventional information, together with parameters of tissue characterization. The apparatus is fast and, over a broad diagnostic frequency range, may be used in conjunction with conventional equipment employing transducers.