559 Dirk Saerens and Serge Muyldermans (eds.), Single Domain Antibodies: Methods and Protocols, Methods in Molecular Biology, vol. 911, DOI 10.1007/978-1-61779-968-6_35, © Springer Science+Business Media, LLC 2012 Chapter 35 Molecular Imaging Using Nanobodies: A Case Study Nick Devoogdt, Catarina Xavier, Sophie Hernot, Ilse Vaneycken, Matthias D’Huyvetter, Jens De Vos, Sam Massa, Patrick De Baetselier, Vicky Caveliers, and Tony Lahoutte Abstract Molecular imaging is a noninvasive method to measure specific biological processes in animal models and patients using imaging. In recent years there has been a tremendous evolution in hardware and software for imaging purposes. This progress has created an urgent need for new labeled targeted molecular probes. The unique physicochemical and pharmacokinetic properties of Nanobodies match the requirements of the ideal molecular imaging tracer. Preclinical studies show strong and specific targeting in vivo with rapid clearance of unbound probe resulting in high contrasted images at early time points after intravenous administration. These data suggest that the Nanobody platform might become a generic method for the development of next generation molecular imaging probes. Key words: Molecular imaging, Biodistribution, SPECT, PET , Radiochemistry , Radionuclide, Fluorescence Molecular imaging is aimed at the noninvasive investigation of cellular and molecular events in living subjects. The key advantage of this imaging methodology is that a biological process can be investigated in its native environment in the intact living individual (animal or human) (1). The most sensitive methods are currently based on radionuclide and optical imaging. The cameras that are used for radionuclide molecular imaging include Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) systems often in combination with an anatomical imaging device such as an X-ray based Computed Tomography (CT) scanner or Magnetic Resonance Imaging system (see Fig. 1). Optical imaging is performed using a sensitive cooled charge coupled device (CCD). 1. Introduction