Microbubbles as a novel contrast agent for brain MRI

Gas-filled microbubbles have the potential to become a unique MR contrast agent due to their magnetic susceptibility effect, biocompatibility and localized manipulation via ultrasound cavitation. In this study, two types of microbubbles, custom-made albumin-coated microbubbles (A-MB) and a commercially available lipid-based clinical ultrasound contrast agent (SonoVue®), were investigated with in vivo dynamic brain MRI in Sprague-Dawley rats at 7 T. Microbubble suspensions (A-MB: 0.2 mL of ∼ 4% volume fraction; SonoVue®: 0.2 mL of ∼ 3.5% volume fraction) were injected intravenously. Transverse relaxation rate enhancements (ΔR2⁎) of 2.49 ± 1.00 s− 1 for A-MB and 2.41 ± 1.18 s− 1 for SonoVue® were observed in the brain (N = 5). Brain ΔR2⁎ maps were computed, yielding results similar to the cerebral blood volume maps obtained with a common MR blood pool contrast agent. Microbubble suspension ΔR2⁎ was measured for different volume fractions. These results indicate that gas-filled microbubbles can serve as an intravascular contrast agent for brain MRI at high field. Such capability has the potential to lead to real-time MRI guidance in various microbubble-based drug delivery and therapeutic applications in the central nervous system.