Evaluation of dose distribution of molecular delivery after blood-brain barrier disruption by focused ultrasound with treatment planning.

The permeability of the blood-brain barrier (BBB) can be enhanced by focused ultrasound (FUS) in localized regions with applications of ultrasound contrast agent (UCA). The purpose of this study was to evaluate the dose distribution of Evans blue (EB) in the targeted brain by sonication with treatment strategy. FUS exposure was applied with an ultrasound frequency of 1 MHz, a 5% duty cycle and a repetition frequency of 1 Hz. Single sonication with two doses of UCA and two sonications at the same location or an interval of 3 mm to induce BBB disruption for assessing dose distribution. The permeability of the BBB was measured quantitatively based on EB extravasation. Gadolinium deposition was monitored by contrast enhanced MR imaging for dose distribution of the focal plane. Hematoxylin and eosin staining was performed for histologic observation. No significant difference was found for EB in the focal regions between the single sonication with UCA at a dose of 300 μL/kg and repeated sonication with UCA at a lower dose of 150 μL/kg. There was a sharper dose distribution in the brain with repeated sonication at the same location, compared with the brain receiving two sonications at an interval of 3 mm. Compared with a single sonication with UCA at a dose of 150 μL/kg, the histologic evaluation of the sonicated regions indicated that more erythrocytes were seen in the brain treated with single sonication at a higher dose of 300 μL/kg or repeated sonication at a dose of 150 μL/kg. This study demonstrated that the dose distribution of molecular delivery could be regulated by sonication with treatment planning.