An ultrasonic intracranial sonothrombolysis pressure amplitude is pre-quantified by using an ultrasound-scanner control unit (110) having an increasing and / or decreasing mode and designed for: with respect to a current mode, interrogating a blockage site iteratively so as to progressively and respectively increase or decrease a pressure amplitude of ultrasound being emitted to the site at which bubbles (144) for oscillating that is caused by the emitted ultrasound are present; iteration to iteration, deriving, from echoes of the emitted ultrasound, a magnitude of an energy of a signal; and automatically identifying, for the quantifying, an iteration that, in comparison with a just-previous iteration, fails to increase the magnitude. The interrogating may span a region that contains or goes through: the obstruction; another part of the blood vessel; and bubble circulation within a neighboring vessel and a neighboring capillary (136). The deriving can be based on an ultraharmonic signal, with band-pass filtering being utilized to extract the ultraharmonic signal from returning signals differenced to remove stationary content.