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.