Monitoring Blood-Brain Barrier Opening in Rats with a Preclinical Focused Ultrasound System

We used a rat model with a jugular vein catheterization, which enables rapid medication administration and stable cavitation monitoring during focused ultrasound procedure. This model allows precise control of microbubble infusion and contrast agent delivery. It can help improve BBB opening studies and enhance reproducibility in preclinical research.

Ensuring that the reproducibility and precision of BBB opening in small animal models, sonication parameters and types of microbubbles, avoiding potential brain damage, and monitoring acoustic emissions to ensure safe and successful treatments. To begin, remove the hair of an anesthetized rat. After confirming proper anesthesia, place a sharp pointer at the position of the Bregma on the rat skull and save the position in the system.

Then, apply ultrasound gel to the rat skull and place the water coupling bag along with a transducer with one megahertz frequency on top of the gel. On the control computer, click on Load to load the pre-registered rat images. Then, select the number of focal spots and acoustic pressure for the procedure.

Next, click on Motion test within the treatment module to ensure that the transducer can shift between spots within a burst period. Fill a five milliliter syringe with additive-free 0.9%sodium chloride solution. Now, place the pin in the center of the vial's rubber stopper.

Press down firmly until the spike is fully inserted into the stopper. Connect the vented dispensing pin to the syringe, insert it in the stopper, and then push the plunger rod to empty the entire five milliliter syringe into the vial, and shake the vial vigorously for 20 seconds to mix all the contents. Invert the syringe and slowly withdraw the intended volume of the suspension into it.

Use an infusion pump to deliver microbubbles to a rat and perform sonication in the left hippocampus of the brain. After completing the sonication, place the rat in a prone position inside the preclinical 3T cryogen-free scanner on a table. Then, inject gadolinium-based MRI contrast agents after the T1 weighted magnetic resonance gradient echo sequence and acquire post-gadolinium images.

Following gadolinium administration, a significant increase in the magnetic resonance signal intensity was observed at the target regions across three experiments. Dynamic contrast-enhanced MRI revealed that the most significant change in signal intensity occurred seven to eight minutes after the contrast agent bolus injection. T1 weighted and T2 weighted images displayed a region of blood-brain barrier opening, while no significant changes were noted in the T1 map before gadolinium administration.