The use of the wavelet transform for improvement of axial resolution of pulse-echo ultrasonic image

Axial resolution of the pulse-echo ultrasonic image depends on pulse duration. Therefore, inverse filtering methods have been proposed to improve the resolution. The center frequency of pulse wave, however, shifts to a lower frequency as it travels in biological media, so that pulse duration becomes longer. In addition to this problem, pulse waves reflected in deep regions cannot be recognized due to their low signal to noise ratios. The authors propose a method using the wavelet transform to improve the resolution. The wavelet transform is a method for time-frequency analysis. The incident pulse wave is used as the mother wavelet in this method. Simulation results show that it is possible to improve axial resolution and to detect reflective index in noise by this method.