SECOND HARMONIC IMAGING FROM PULSE-ECHO SIGNALS OF CONTRAST-ASSISTED ULTRASOUND

Increasing interest in extending the diagnostic capabilities of medical ultrasound imaging by utilizing ultrasound contrast agents (UCAs) has heightened the need for suitable harmonic separation models. This article describes the second harmonic frequency characteristic and second harmonic image generation from pulse-echo signals of UCA. Based on the differences in frequency of ultrasound data from two different media, ultrasound signals are classified into two classes, i.e., UCA and tissue. We show the frequency characteristic of the UCA signals from an in vivo target to demonstrate this nonlinear behavior. Then, the difference in frequency components of the UCA and tissue data is used as a reference to design a linear bandpass filter (LBF) in order to separate the UCA signals from tissue echoes. The LBF is designed using the Parks-McClellan algorithm. We find that the appropriate fractional bandwidth (FB) and stopband attenuation of the LBF are 15 %- 25% and 40- 50 dB, respectively. The imaging quality for medical ultrasound purposes, by utilizing the information from the frequency contents of contrast-assisted ultrasound data, has been improved. Results show that the images produced from the output signals of the optimal LBF are superior to the original B-mode images both in terms of contrast and spatial resolution