[Comment] Evaluating drug delivery enhancement following ultrasound treatment

Focused ultrasound in conjunction with circulating microbubbles is gaining pace as a new method for non-invasive and targeted drug delivery across biological barriers, such as the blood–brain barrier or the blood–tumour barrier.1 The gold-standard method of confirming the success of ultrasound treatment has thus far been acquiring a contrast-enhanced MRI scan with a gadolinium-based contrast agent. Although contrast-enhanced MRI provides invaluable information about the location and extent of blood–brain barrier opening, it does not provide a quantifiable estimate of drug delivery enhancement.