ABSTRACT
A nanoparticle (NP) is a dynamic space for research and can be used in many fields due to its fascinating characteristics like enhanced surface-to-volume ratio, increased magnetic property and NIR absorption, etc. Due to this they play a crucial role in clinical therapy and diagnosis. Among several diagnostic tools magnetic resonance imaging (MRI), a noninvasive technique, is superior over other imaging modalities including high-resolution imaging, nonionizing radiation, better soft tissue contrast, and multiplanar imaging capabilities. Different types of contrast agents (CAs) can be used to improve the contrasting efficiency of an image by locally changing relaxation rates. In recent times concerns have ascended regarding the long-term safety of clinically used hydrophilic, mononuclear Gd3+-based chelates. This has stimulated researchers to develop new targeted or smart like CA with enhanced MR contrasting efficiency. This comprehensive chapter describes the theoretical model based on the inner sphere Solomon-Bloembergen-Morgan (SBM) theory and outer sphere diffusion theory to explain the contrast mechanism of MRI CAs and their interaction with water protons. From there we attribute different strategies which are required for the improvement of the contrast efficiency of a CA. Next we describe different factors which affect r1 and r2 value of a CA. After that we review different types of CA along with the limitation of commercially available Gd(III)-based CA. Finally we survey approaches to develop CAs followed by direct targeting or responsive, known as smart CA. In this context, particular attention has been dedicated to the diverse multimodal imaging CAs encompassing both Prussian blue (PB) and Prussian blue analogous (PBA) NPs which serve as MR-PA imaging-based bimodal CAs.
