An apparatus configured for, with respect to obstructed flow in a lumen within a brain , bubbles being located at a site of the obstruction, quantifying a pressure amplitude of ultrasound to be applied to, via oscillation of said bubbles, alleviate said obstructed flow, said apparatus comprising: an ultrasound-scanner control unit configured with at least one of an increasing mode and a decreasing mode and for: with respect to a current mode from among said at least one, interrogating said site iteratively so as to progressively and respectively increase or decrease a pressure amplitude of ultrasound being emitted to said site at which bubbles for oscillating that is caused by the emitted ultrasound are present; iteration to iteration, deriving, from echoes of said emitted ultrasound, a magnitude of an energy of a signal; and automatically identifying, for said quantifying, an iteration, from among the iterations, that, in comparison with a just-previous iteration from among said iterations, fails to increase said magnitude, characterised in that said pressure amplitude of ultrasound being emitted is an excitation amplitude, said control unit being further configured for, upon said identifying, fine-tuning by: a) continuing with the iterative interrogating and identifying, using, as a starting point, said excitation amplitude of said just-previous iteration and correspondingly, in accordance with said current mode, continuing to increase or decrease said excitation amplitude progressively with a corresponding increase or decrease that is smaller than used prior to said identifying (S370); or b) continuing with the iterative interrogating and identifying, using, as a starting point, said excitation amplitude of the current iteration and switching over from progressively increasing to progressively decreasing said excitation amplitude, or vice versa, with a corresponding increase or decrease that is smaller than used prior to said identifying. with respect to a current mode from among said at least one, interrogating said site iteratively so as to progressively and respectively increase or decrease a pressure amplitude of ultrasound being emitted to said site at which bubbles for oscillating that is caused by the emitted ultrasound are present; iteration to iteration, deriving, from echoes of said emitted ultrasound, a magnitude of an energy of a signal; and automatically identifying, for said quantifying, an iteration, from among the iterations, that, in comparison with a just-previous iteration from among said iterations, fails to increase said magnitude, characterised in that said pressure amplitude of ultrasound being emitted is an excitation amplitude, said control unit being further configured for, upon said identifying, fine-tuning by: a) continuing with the iterative interrogating and identifying, using, as a starting point, said excitation amplitude of said just-previous iteration and correspondingly, in accordance with said current mode, continuing to increase or decrease said excitation amplitude progressively with a corresponding increase or decrease that is smaller than used prior to said identifying (S370); or b) continuing with the iterative interrogating and identifying, using, as a starting point, said excitation amplitude of the current iteration and switching over from progressively increasing to progressively decreasing said excitation amplitude, or vice versa, with a corresponding increase or decrease that is smaller than used prior to said identifying. <EOS>