Using microbubbles as an MRI contrast agent for the measurement of cerebral blood volume

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Pharmacology

Background:

• Microbubbles (MBs) offer potential as intravascular susceptibility contrast agents for MRI due to their unique gas-liquid interface properties.
• Key differences in MB characteristics (size, hemodynamics) compared to standard gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) may affect MRI outcomes.

Purpose of the Study:

• To quantitatively investigate the correlation between MB-induced susceptibility effects and relative cerebral blood volume (rCBV) derived from Gd-DTPA using dynamic susceptibility contrast MRI (DSC-MRI).
• To assess the influence of microbubble characteristics, particularly time to peak (TTP), on MRI-based rCBV estimation.

Main Methods:

• Custom-made microbubbles (mean diameter 0.92 µm) were administered to 16 rats.
• Dynamic susceptibility contrast MRI (DSC-MRI) at 4.7-T was used to compare MB-induced susceptibility effects (ΔR(2*MB)) with Gd-DTPA-derived rCBV (rCBV(Gd)).
• The correlation between ΔR(2*MB) and rCBV(Gd) was analyzed, considering the effect of time to peak (TTP) and maximum signal change (MSC).

Main Results:

• A significant influence of time to peak (TTP) was observed on the correlation between MB susceptibility effects and rCBV(Gd).
• A notable dependence between TTP and maximum signal change (MSC) was identified.
• MBs with longer TTPs demonstrated a stronger correlation with rCBV(Gd).

Conclusions:

• Microbubbles with longer TTPs are suitable for estimating rCBV using DSC-MRI.
• The time to peak (TTP) is a critical parameter influencing the accuracy of MB-based contrast MRI for rCBV quantification.