Dr. Elisa Konofagou, professor of biomedical engineering and radiology at Columbia University, has shown for the first time that the size of molecules crossing the blood brain barrier (BBB) can be manipulated through acoustic pressure generated by an ultrasound beam. Delivering drugs to the brain is exceptionally 
difficult as most small molecules and all large molecules cannot cross.
Konofagou combined microbubbles, bubbles with lipid or protein shells that are filled with gas, and adjustments of acoustic pressure to test the delivery of various sized sugar molecules (Dextran) to the hippocampus. By choosing a specific pressure, Konofagou was able to cause the microbubbles to oscillate and create openings in the BBB with minimal microscopic damage. She discovered that lower pressures allow smaller molecules to go through the barrier while higher pressures allow larger molecules to go through the barrier. Her experiment included setting the left hippocampus of the mouse model to be the area of interest and the right side of the hippocampus to be the control. Using fluorescence imaging, Konofagou was able to confirm the greater uptake of the molecules in the left hippocampus of the mouse model in comparison to the right hippocampus.
Columbia University statement: New Non-Invasive Technique Controls the Size of Molecules….
Study in the Journal of Cerebral Blood Flow and Metabolism (Under Publications): Blood Barrier Opening…