In vivo study of microbubbles as an MR susceptibility contrast agent

Abstract

The potential application of gas microbubbles as a unique intravascular susceptibility contrast agent for MRI has not been fully explored. In this study, the MR susceptibility effect of an ultrasound microbubble contrast agent, Optison®, was studied with rat liver imaging at 7 T. Optison® suspension in two different doses (0.15 mL/kg and 0.4 mL/kg) was injected into rats, and induced transverse relaxation rate increases (ΔR 2*) of 29.1 ± 1.6 s -1 (N = 2) and 61.5 ± 12.9 s -1 (N = 6), respectively, in liver tissue. Liver uptake of intact albumin microbubbles was observed 10 min after injection. Eight of the 16 rats studied showed no susceptibility enhancement. This is probably attributable to the intravascular microbubble growth due to transmural CO 2 supersaturation in the cecum and colon in small animals that causes microbubble aggregation and trapping in the inferior vena cava (IVC). In vitro ΔR 2* measurements of Optison® suspension at different concentrations are also reported. © 2004 Wiley-Liss, Inc.