In vivo study of microbubbles as an MR susceptibility contrast agent

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Pharmacology

Background:

• Gas microbubbles are being explored as intravascular susceptibility contrast agents for MRI.
• Their application remains limited due to challenges in controlling their behavior in vivo.

Purpose of the Study:

• To investigate the MR susceptibility effect of the ultrasound microbubble contrast agent, Optison, in rat liver imaging at 7 Tesla.
• To assess the dose-dependent effects and potential limitations of microbubble contrast agents.

Main Methods:

• In vivo MRI of rat livers at 7 T after intravenous injection of Optison at two different doses (0.15 mL/kg and 0.4 mL/kg).
• Measurement of induced transverse relaxation rate increases (deltaR2*).
• In vitro deltaR2* measurements of Optison suspension at various concentrations.

Main Results:

• Optison administration resulted in dose-dependent increases in liver deltaR2* (29.1 ± 1.6 s⁻¹ at 0.15 mL/kg, 61.5 ± 12.9 s⁻¹ at 0.4 mL/kg).
• Liver uptake of intact microbubbles was observed 10 minutes post-injection.
• Significant susceptibility enhancement was absent in 50% of rats, likely due to intravascular microbubble aggregation in the inferior vena cava.

Conclusions:

• Gas microbubbles, like Optison, can induce MR susceptibility effects in liver tissue.
• Microbubble aggregation and trapping in the inferior vena cava represent a significant challenge for their consistent application as intravascular MRI contrast agents in small animals.