['Ultrasound', '(', 'US', ')', 'can', 'initiate', 'the', 'release', 'of', 'drugs', 'from', 'liposomes', 'via', 'an', 'event', 'called', 'inertial', 'cavitation', ',', 'whereby', 'the', 'rarefactional', 'phase', 'of', 'an', 'ultrasound', 'wave', 'causes', 'the', 'expansion', 'of', 'a', 'gas', 'bubble', 'followed', 'by', 'a', 'violent', 'collapse', 'due', 'to', 'the', 'inertia', 'of', 'the', 'surrounding', 'media', '.']