Ultrasound to open the blood-brain barrier in Alzheimer’s disease is the latest in the growing field of focused ultrasound. Most people think of ultrasound as a way to take fuzzy black-and-white pictures of a fetus in the womb. But with focused ultrasound, doctors use the sound waves to actively treat a condition rather than passively produce images of it. It’s already an FDA-approved treatment for essential tremor and is an approved treatment for Parkinson’s disease outside the United States. That’s under review here as well.