Abstract: Cavitation activities induced by high intensity focused ultrasound (HIFU) pulses were detected and quan- tiffed in vitro, based on area measurements of hyperechoic regions observed in B-mode ultrasound images. A two dimensional imaging processing algorithm was proposed to eliminate the moving interference bands in B-mode images. The temporal evolution of bubble clouds, generated by HIFU exposures with constant working frequency and pulse repetition frequency but varied driving pressures and pulse lengths, were analyzed by measuring time-varying behaviors of hyperechoic region areas recorded in B-mode images. The results show that the proposed imaging processing algorithm is effective to remove the bright interference masks in B-mode image, which makes HIFU-induced cavitation bubble clouds can be monitored and evaluated by B-mode imaging in real-time. With the increasing acoustic energy deposited in the tissue phantom, the hyperechoic region area in B-mode image indicating more violent cavitation activity can be enlarged, while the initial generation time of HIFU-induced cavitation bubbles will be shortened. This study is important for further optimization of HIFU therapy.