1 Metal Ions in Bio-Imaging Techniques: A Short Overview

Abstract

Endogenous metal ions play a pivotal role in many biological systems, ranging from transition metal cofactors in essential enzymes to calcium ions in bones and cartilages. The idea of using exogenous metal ions as a diagnostic tool dates back to the first half of the 20th century when barium salts were orally administered to patients undergoing X-ray examination. Since that time, the field of molecular imaging has experienced remarkable changes, driven by the technological advances offered by modern imaging techniques. Each year brings hundreds of new molecular probes that are reported in preclinical studies and a few dozen enter human clinical trials. Such a massive data flow requires an appropriate classification, both by the type of imaging modality and chemical structure of the molecular probe. In this introductory chapter, recent advances and challenges in metal-based molecular imaging are discussed in four individual sections, covering magnetic resonance imaging (MRI), the nuclear medicine techniques of positron emission tomography (PET) and single photon emission computed tomography (SPECT), X-ray computed tomography (CT), and luminescent imaging, while a final section is dedicated to multimodal imaging, encompassing probes that can simultaneously produce a diagnostic signal detected by more than one imaging mode. Each of these sections, in turn, is subdivided into several parts, each dealing with a particular class of molecular probes based on their chemical structure, as well as the combination of imaging with therapy. We highlight representative examples of the different types of probes.