High-frequency ultrasound Doppler detection using fundamental pulse inversion technique

Swept-scan imaging mode is often utilized in high-frequency ultrasound Doppler estimation of blood flow. However, tissue spectral broadening effect in swept-scan system severely limits the detection of low-velocity flow especially at high scanning speed of motor. To alleviate the effect of wall filtering on low-velocity blood signal, the suppression of tissue Doppler signal using micro-bubble contrast agent and non-linear imaging can be helpful. With the method of fundamental pulse-inversion Doppler (FPID), the non-linear bubble signal can be isolated from the linear tissue signal at fundamental frequency by low-pass filtering in the Doppler domain to reduce the clutter interference. Results show that the FPID helps to retain the low-velocity blood flow signal in color Doppler imaging and thus improves the efficacy of blood flow detection. With different lateral scanning speed of motor (V_motor), the values of color-pixel density (CPD) with FPID are 0.63 (V_motor = 4mm/s), 0.65 (V_motor = 8mm/s) and 0.58 (V_motor = 16mm/s). It shows that FPID is less susceptible to the tissue spectral broadening effect The results also show that, with FPID method, the flow signal-to-clutter ratio (SCR) increases by 7.7dB (P <; 0.001) and the CPD increases by 20 % (P <; 0.001) in the case of 3mm/s of blood flow velocity and 16mm/s lateral scanning speed of motor.