Chem. Eng. J. 2019, 289-298



Magnetic Resonance Imaging (MRI) is a non-invasive imaging technique that produces three dimensional detailed anatomical images with high soft tissue contrast and spatial resolution. By now MRI contrast agents have become an indispensable part of MRI procedure for the diagnostics of some diseases, since their addition in many cases improves sensitivity and specificity and therefore provide better distinction of pathological tissues. There are two main types of MRI contrast agents, paramagnetic Gd compounds and superparamagnetic iron oxide nanoparticles (SPIOs). Paramagnetic Gd compounds affect the spin-lattice (T1) contrast of water protons, whereas SPIOs shorten the spin-spin relaxation time (T2) of water molecules and are used for T2 imaging. However, a single MR contrast process has some inherent drawbacks, for example: (1) disturbances originating from calcification, bleeding, or metal deposits in T2 imaging and (2) insufficient signal intensity in disease tissue for T1 imaging. These drawbacks are difficulty in discrimination between normal tissue and disease tissue and may seriously limit accurate interpretation for the diagnosis image. Therefore, developing multifunctional imaging modes using a one-scanner device to obtain more accurate diagnosis information is necessary.

Recently, Professor Zou Duohong from Shanghai Jiao Tong University School and Professor Xu Yunsheng from Wenzhou Medical University reported an efficient strategy to prepare a highperformance dual-mode MRI contrast agent via modifying the nanostructure and increasing the number of water interactions. HSiO2@GdIONC has a nested, mesoporous core structure and can effectively bind abundant water molecules via physical absorption and hydrogen-bond and oxygen-vacancy interactions, dramatically improving the T1 and T2 contrast ability. In addition, compared with that of bare GdIONC (10.5), the r2/r1 ratio of HSiO2@GdIONC decreased to 8.3, effectively preventing the disturbance of T1 and T2 imaging and allowing HSiO2@GdIONC to exhibit an optimal dual-mode contrast ability. Based on the results of the cell and animal experiments, HSiO2@GdIONC showed better T1- and T2-weighted MR contrast in the liver region than bare GdIONC.