Abstract: Provided herein are nanoparticle-based gadolinium (Gd) agents which may be used, e.g., in T1-weighted MR imaging (MRI). In various embodiments, dual-Gd liposomal agents are provided which contain both core-encapsulated Gd as well as surface-conjugated Gd. In various embodiments, these agents were observed to deliver a higher concentrations of Gd and result in substantial improvements in signal to noise ratios and contrast to noise ratios. Also provided are methods for in vivo imaging and/or treating diseases such as cancer or tumor in a subject.