Fig. 3From: Nanosensitizers for sonodynamic therapy for glioblastoma multiforme: current progress and future perspectivesPhysiological and pathophysiological structures of the blood–brain barrier (BBB). BBB structure alterations in brain tumors and types of small molecules that cross the BBB. a Tight junction in physiological status, < 1 nm. b Tight conjunction in tumor bearing status, > 7 nm. c Approximately 20 nmBack to article page