Morphological imaging techniques are very limited in their ability to evaluate the early efficacy of tumor therapies, with the limitation of being more reflective and lagging. Many of the newer therapies are cytostatic, and tumor necrosis or lack of tumor progression is associated with a good response to treatment even in the absence of tumor shrinkage; therefore, there is an increasing need to develop techniques for the assessment of tumor efficacy. Magnetic resonance imaging (MRI), with the help of a variety of contrast mechanisms and probes, provides excellent soft-tissue imaging, high-quality anatomical signals as well as reflecting certain functional states of the tumor and molecular biological information. It can be used to differentiate between cancer and normal tissue, to noninvasively monitor tumor growth, and to identify changes in the tumor and its microenvironment in response to treatment. This review will discuss the role of magnetic resonance imaging in the assessment of tumor efficacy, with a focus on presenting research advances in magnetic resonance molecular imaging and its probes in the assessment of tumor efficacy.

Inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of colortunable Gd-Zn-Cu-In-S/ZnS (GZCIS/ZnS) quantum dots (QDs) with stable crystal structure has been successfully synthesized and utilized for magnetic resonance (MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T₁ MR contrast as well as "color-tunable" photoluminescence (PL) in the range of 550–725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield (QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin (BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both HeLa and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imaging.