Theranostic Imaging Agents: Integrating Molecular Diagnostics, Precision Therapeutics, and Artificial Intelligence

Theranostic imaging agents combine molecular diagnosis, targeted therapy and monitoring of treatment response into a single paradigm of precision medicine. This review summarizes the current development and translational landscape of theranostic imaging agents, covering molecular targets, imaging platforms, principles of agent design, nanotheranostics, radiotheranostics, and disease-specific applications. Particular emphasis is given to clinically validated and emerging targeting strategies using prostate-specific membrane antigen, somatostatin receptors, fibroblast activation protein, C-X-C Chemokine Receptor 4 (CXCR4), Human Epidermal Growth Factor Receptor 2 (HER2) and other disease-associated biomarkers. Moreover, the review addresses Positron Emission Tomography (PET), Single-Photon Emission Computed Tomography (SPECT), Magnetic Resonance Imaging (MRI), optical, photoacoustic, Raman and multimodal imaging approaches, therapeutic payloads, stimulus-responsive systems, and pharmacokinetic optimization. Moreover, emerging applications of artificial intelligence, radiomics, radiogenomics, spatial and single-cell multiomics, liquid biopsy, digital pathology, personalized dosimetry, and digital twins are evaluated for their potential to improve patient stratification, treatment selection, response assessment and adaptive therapy. Despite tremendous progress, clinical translation is hampered by target heterogeneity, off-target accumulation, radionuclide availability, manufacturing complexity, dosimetric uncertainty, regulatory requirements, limited clinical validation, data interoperability, cost and unequal access. This review, overall, emphasizes the convergence of molecular imaging, targeted therapeutics, nanotechnology, and artificial intelligence in the development of next-generation theranostic platforms, and outlines critical priorities for their clinical translation.