A stroke therapy system for treating cranial vascular obstructions comprising: a transducer array headset which maintains an ultrasonic transducer array (10a, 10b, 122) in acoustic contact with the head of a subject; an image processor (26, 28, 30, 32, 34), coupled to the ultrasonic transducer array, which produces images of blood flow in the cranium of the subject in an imaging mode of the ultrasonic transducer array; an image display, coupled to the image processor, which produces an image of the cranial vasculature; characterized in that: the ultrasonic transducer array is operable in a therapy mode to direct a therapeutic beam at an obstruction site in the cranium of the subject, said therapeutic beam being capable of breaking up microbubbles, introduced to the subject's bloodstream, at the obstruction site and comprising a series of ultrasonic beam pulses having a duty cycle of 50% or less, wherein, in the therapy mode, the ultrasonic therapeutic beam is iteratively: delivered to the obstruction site for a period of 100-300 milliseconds, to thereby break up substantially all of the microbubbles at the obstruction site; and subsequently inhibited, to allow new microbubbles to reinfuse the obstruction site. a transducer array headset which maintains an ultrasonic transducer array (10a, 10b, 122) in acoustic contact with the head of a subject; an image processor (26, 28, 30, 32, 34), coupled to the ultrasonic transducer array, which produces images of blood flow in the cranium of the subject in an imaging mode of the ultrasonic transducer array; an image display, coupled to the image processor, which produces an image of the cranial vasculature; characterized in that: the ultrasonic transducer array is operable in a therapy mode to direct a therapeutic beam at an obstruction site in the cranium of the subject, said therapeutic beam being capable of breaking up microbubbles, introduced to the subject's bloodstream, at the obstruction site and comprising a series of ultrasonic beam pulses having a duty cycle of 50% or less, wherein, in the therapy mode, the ultrasonic therapeutic beam is iteratively: delivered to the obstruction site for a period of 100-300 milliseconds, to thereby break up substantially all of the microbubbles at the obstruction site; and subsequently inhibited, to allow new microbubbles to reinfuse the obstruction site. the ultrasonic transducer array is operable in a therapy mode to direct a therapeutic beam at an obstruction site in the cranium of the subject, said therapeutic beam being capable of breaking up microbubbles, introduced to the subject's bloodstream, at the obstruction site and comprising a series of ultrasonic beam pulses having a duty cycle of 50% or less, wherein, in the therapy mode, the ultrasonic therapeutic beam is iteratively: delivered to the obstruction site for a period of 100-300 milliseconds, to thereby break up substantially all of the microbubbles at the obstruction site; and subsequently inhibited, to allow new microbubbles to reinfuse the obstruction site. delivered to the obstruction site for a period of 100-300 milliseconds, to thereby break up substantially all of the microbubbles at the obstruction site; and subsequently inhibited, to allow new microbubbles to reinfuse the obstruction site.