Advances in multifunctional nano-sized CT contrast agents

Computed tomography (CT) is one of the most widely used noninvasive clinical imaging modalities because of its wide availability, low cost, high efficiency and high resolution. Although the resolution of CT is much higher than that of conventional radiography and many other imaging techniques, it is still difficult to distinguish subtle changes of soft tissues because of physical limitations. To increase the contrast of soft tissues and improve the accuracy of disease diagnosis, a variety of CT contrast agents have been developed. Small iodinated compounds have been widely used as clinical CT contrast agents, but their toxicity and short circulation time restrict their further application. To resolve these problems, nanosized CT contrast agents have been developed. In addition to iodine, nanoparticles based on heavy atoms such as gold, tantalum, lanthanides, and bismuth have been investigated as more efficient CT contrast agents than small iodinated compounds. These novel nanosized CT contrast agents have high biocompatibility and long circulation times, which are advantageous for visualization of blood vessels and tumors. Moreover, the combination of CT with other imaging techniques, such as magnetic resonance imaging and ultrasound imaging, could realize higher sensitivity and more personalized diagnostic information. In particular, theranostic CT contrast agents that integrate diagnosis with therapy in a single nanoplatform may serve as a nanomedicine capable of both noninvasive imaging and remote-controlled therapy. Herein, we introduce the principles of CT imaging and commonly used nanoscale CT contrast elements, including iodine, gold, bismuth, tantalum, and lanthanides. The recent advances, future development and existing problems of multifunctional nanosized CT contrast agents are reviewed.