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



The susceptibility differences at the gas–liquid interface of microbubbles (MBs) allow their use as an intravascular susceptibility contrast agent for in vivo MRI. However, the characteristics of MBs are very different from those of the standard gadolinium-diethylenetriaminepentaacetic acid (Gd-DPTA) contrast agent, including the size distribution and hemodynamic properties, which could influence MRI outcomes. Here, we investigate quantitatively the correlation between the relative cerebral blood volume (rCBV) derived from Gd-DTPA (rCBVGd) and the MB-induced susceptibility effect (ΔR2*MB) by conventional dynamic susceptibility contrast MRI (DSC-MRI). Custom-made MBs had a mean diameter of 0.92 µm and were capable of inducing 4.68 ± 3.02% of the maximum signal change (MSC). The MB-associated ΔR2*MB was compared with rCBVGd in 16 rats on 4.7-T MRI. We observed a significant effect of the time to peak (TTP) on the correlation between ΔR2*MB and rCBVGd, and also found a noticeable dependence between TTP and MSC. Our findings suggest that MBs with longer TTPs can be used for the estimation of rCBV by DSC-MRI, and emphasize the critical effect of TTP on MB-based contrast MRI. Copyright © 2013 John Wiley & Sons, Ltd.