Ultrasound tomographic imaging with broadband pulse

Abstract

Techniques in ultrasound tomographic imaging are investigated for high resolution and faithful image reconstruction using broadband pulse. First, we investigated a numerical technique for the calculation of pulse-echo reflected from point and line reflectors based on three-dimensional diffraction theory. The resulting formular has the form efficiently used in the diffraction simulation of surface acoustic wave filters. Second, the prior inverse filtering technique, in which the transducer is excited by a synthesized signal corresponding to the impulse response of the inverse filter, is applied to ultrasonic imaging for the improvement of the axial resolution. Diffraction effects of transducers and scatterers are discussed in view of the performance of the inverse filter. Experimental results demonstrating the diffraction effects on the pulse-echo duration are presented. It is shown that the axial resolution can be increased without noise amplification by a factor of two when the prior inverse filtering technique is applied to the medical B-scan image. Third, several tomographic imaging techniques are investigated for the faithful image reconstruction of ultrasound reflectivity. A deconvolution kernel, which can improve the resolution without additional computation time compared to conventional filter kernels, is suggested, and it is shown experimentally that the deconvolution kernel is efficient in improving the resolution for relatively strong singal. Through a series of experiments, basic characteristics of ultrasound reflection tomography such as the effects of the view number and the view angle are examined and compared to the transmission CT, i.e., attenuation CT and velocity CT. Also, the effect of acoustic speed variation, i.e., inhomogenuous index of refraction, on ultrasonic reflection tomography is examined by computer simulation and experiment. The result shows that the resolving power of reflection tomography is lowered and structural distortions ar...