**Ernesto Forte 1,**†**, Dario Fiorenza 1,**†**, Enza Torino 2,3,4,\*, Angela Costagliola di Polidoro 2,3, Carlo Cavaliere 1, Paolo A. Netti 2,3,4, Marco Salvatore <sup>1</sup> and Marco Aiello <sup>1</sup>**


Received: 19 November 2019; Accepted: 24 December 2019; Published: 29 December 2019

**Abstract:** The development of integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners opened a new scenario for cancer diagnosis, treatment, and follow-up. Multimodal imaging combines functional and morphological information from different modalities, which, singularly, cannot provide a comprehensive pathophysiological overview. Molecular imaging exploits multimodal imaging in order to obtain information at a biological and cellular level; in this way, it is possible to track biological pathways and discover many typical tumoral features. In this context, nanoparticle-based contrast agents (CAs) can improve probe biocompatibility and biodistribution, prolonging blood half-life to achieve specific target accumulation and non-toxicity. In addition, CAs can be simultaneously delivered with drugs or, in general, therapeutic agents gathering a dual diagnostic and therapeutic effect in order to perform cancer diagnosis and treatment simultaneous. The way for personalized medicine is not so far. Herein, we report principles, characteristics, applications, and concerns of nanoparticle (NP)-based PET/MRI CAs.

**Keywords:** multimodal imaging; hybrid imaging; positron emission tomography/magnetic resonance imaging (PET/MRI), nanotechnology; nanoparticles; in vivo imaging; 3D reconstruction
