To provide a treatment method capable of expanding a blood brain barrier effectively.SOLUTION: In a treatment method of the present invention, an irradiation part 20 of a long-sized ultrasonic catheter 100 equipped with the irradiation part capable of irradiating an ultrasonic wave is caused to move to the vicinity of a blood brain barrier B in a blood vessel. An ultrasonic wave is irradiated from the irradiation part in the vicinity of the blood brain barrier, and a stimulus is applied to a nerve or a peripheral tissue from outside the blood vessel so as to expand the blood brain barrier.SELECTED DRAWING: Figure 6【課題】血液脳関門を効果的に広げることが可能な処置方法を提供する。【解決手段】本発明に係る処置方法は、超音波を照射可能な照射部２０を備えた長尺状の超音波カテーテル１００の照射部を血管内における血液脳関門Ｂの近傍まで移動させ、血液能関門の近傍で照射部から超音波を照射するとともに血管の外部から神経又は周辺組織に刺激を与えて血液脳関門を広げる。【選択図】図６
