An ultrasound diagnostic system and method of detecting thermal diffusion due to injection of high intensity focused ultrasound (HIFU) arc disclosed. According to the embodiments of the present invention, first receive signals are obtained by ultrasound echo signals from the lesion that did not undergo the HIFU and second receive signals are obtained by ultrasound echo signal from the lesion that underwent the HIFU. Center frequencies of the first and second receive signals are detected, while center frequency shift between the first and second receive signals are calculated. A center frequency shift image is formed with the center frequency shift.
