Chow April M, Cheung Jerry S, Wu Ed X
Laboratory of Biomedical Imaging and Signal Processing, Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong.
Annu Int Conf IEEE Eng Med Biol Soc. 2009;2009:4049-52. doi: 10.1109/IEMBS.2009.5333171.
Gas-filled microbubbles have the potential to become a unique intravascular MR contrast agent due to their magnetic susceptibility effect, biocompatibility and localized manipulation via ultrasound cavitation. However, in vivo demonstration of microbubble susceptibility effect is limited so far and microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, two types of microbubbles, custom-made albumin-coated microbubbles (AMBs) and a commercially available lipid-based clinical ultrasound contrast agent (SonoVue), were investigated with in vivo dynamic brain and liver MRI in Sprague-Dawley rats at 7 Tesla. Transverse relaxation rate enhancements (DeltaR2*) maps were computed for brain and liver, yielding results similar to those obtained with a common MR blood pool contrast agent. These results indicate that gas-filled microbubbles can serve as an intravascular MR contrast agent at high field. Enhancement of microbubble susceptibility effect by entrapping monocrystalline iron oxide nanoparticles (MIONs) into microbubbles was also investigated at 7 T in vitro. This is the first experimental demonstration of microbubble susceptibility enhancement for MRI application. This study indicates that gas-filled microbubble susceptibility effect can be substantially increased using iron oxides nanoparticles. With such approach, microbubbles can potentially be visualized with higher sensitivity and lower concentrations by MRI. Such capability has the potential to lead to real-time MRI guidance in various microbubble-based drug delivery and therapeutic applications.
由于其磁化率效应、生物相容性以及通过超声空化进行局部操纵的特性，充气微泡有潜力成为一种独特的血管内磁共振造影剂。然而，到目前为止，微泡磁化率效应在体内的验证还很有限，并且与其他血管内磁共振磁化率造影剂相比，微泡磁化率效应相对较弱。在本研究中，使用7特斯拉的磁共振成像对Sprague-Dawley大鼠的脑和肝脏进行体内动态成像，研究了两种类型的微泡：定制的白蛋白包被微泡（AMB）和市售的基于脂质的临床超声造影剂（声诺维）。计算了脑和肝脏的横向弛豫率增强（DeltaR2*）图，得到的结果与使用普通磁共振血池造影剂获得的结果相似。这些结果表明，充气微泡在高场下可作为血管内磁共振造影剂。还在7特斯拉的体外环境中研究了通过将单晶氧化铁纳米颗粒（MION）包裹在微泡中来增强微泡磁化率效应。这是首次针对磁共振成像应用进行的微泡磁化率增强的实验证明。本研究表明，使用氧化铁纳米颗粒可大幅提高充气微泡的磁化率效应。通过这种方法，微泡有可能通过磁共振成像以更高的灵敏度和更低的浓度被可视化。这种能力有可能在各种基于微泡的药物递送和治疗应用中实现实时磁共振成像引导。
