Characterization of different bubble formulations for blood-brain barrier opening using a focused ultrasound system with acoustic feedback control.

Focused ultrasound combined with bubble-based agents serves as a non-invasive way to open the blood-brain barrier (BBB). Passive acoustic detection was well studied recently to monitor the acoustic emissions induced by the bubbles under ultrasound energy, but the ability to perform reliable BBB opening with a real-time feedback control algorithm has not been fully evaluated. This study focuses on characterizing the acoustic emissions of different types of bubbles: Optison, Definity, and a custom-made nanobubble. Their performance on reliable BBB opening under real-time feedback control based on acoustic detection was evaluated both in-vitro and in-vivo. The experiments were conducted using a 0.5 MHz focused ultrasound transducer with in-vivo focal pressure ranges from 0.1-0.7 MPa. Successful feedback control was achieved with all three agents when combining with infusion injection. Localized opening was confirmed with Evans blue dye leakage. Microscopic images were acquired to review the opening effects. Under similar total gas volume, nanobubble showed a more reliable opening effect compared to Optison and Definity (p < 0.05). The conclusions obtained from this study confirm the possibilities of performing stable opening using a feedback control algorithm combined with infusion injection. It also opens another potential research area of BBB opening using sub-micron bubbles.

Introduction

Purpose Drug delivery with BBB opening

Study Objective To characterize the acoustic emissions of Optison, Definity, and a custom nanobubble and evaluate their ability to achieve reliable blood–brain barrier opening under real-time ultrasound feedback control in vitro and in vivo.

Animal model / Human subject Rattus norvegicus (Sprague Dawley), age not specified (weight 230–300 g), female

Disease model Healthy

Cargo name and characteristics Evans blue dye — small-molecule, albumin-binding tracer dye used as an experimental permeability marker to confirm localized BBB opening (detects leakage into brain tissue)

Outcomes and Safety

Summary of Outcomes Focused ultrasound with bubble agents (Optison, Definity, and a custom nanobubble) produced localized, Evans‑blue–confirmed BBB opening using a real‑time acoustic‑emission feedback algorithm with steady infusion; the nanobubble yielded more reliable opening, longer circulation, lower variability and greater efficacy at lower pressures (p<0.05). Successful parameters included a 0.5 MHz focused transducer with feedback on the ultra‑harmonic (0.75 MHz) using an AUC control threshold of 5,000, infusion administration, and in‑vivo focal pressures in the ~0.1–0.7 MPa range (maintained pressures ≈0.42 MPa for Optison, 0.34 MPa for Definity, 0.23 MPa for nanobubble); ultra‑harmonic activity was detectable for nanobubble around ~0.16–0.21 MPa and broad‑band/inertial cavitation around ~0.47 MPa for all agents.

Duration of biological effect 6-8 minutes

Safety-related matter Overall cellular morphology appeared normal after BBB opening, but endothelial cell changes (wider, more aggregated and uneven morphology) were observed in targeted regions—these changes were more pronounced with Optison and nanobubble; no explicit acute adverse events were reported, and the authors state further studies are required to determine control thresholds that avoid tissue damage.

Brain Region

Visualization unavailable

Ultrasound Parameters

Ultrasound instrument 0.5 MHz focused ultrasound transducer (manufacturer not specified); transducer aperture/diameter: None

FUS Frequency 0.5 MHz; 0.75 MHz; 20 MHz

FUS Pressure 0.1–0.7 MPa (in-vivo focal pressure range; in-vivo pressure sweep), 0.21–1.13 MPa (in-vitro pressure sweep), 0.47 MPa (constant focal pressure in animal experiments), 0.01–0.03 MPa (pressure adjustment step size)

FUS Mode pulsed

Pulse duration 10 ms

Duration of a single FUS session 100 seconds

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: None

Treatment frequency Multiple

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