European Journal of Radiology 78 (2011) 287–295 Contents lists available at ScienceDirect European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad Current status and future perspectives of in vivo small animal imaging using radiolabeled nanoparticles George Loudos a,1 , George C. Kagadis b,∗ , Dimitris Psimadas a,c,1,2 a Department of Medical Instruments Technology, Technological Educational Institute of Athens, AG. Spyridonos 28, Egaleo 12210, Greece b Department of Medical Physics, School of Medicine, University of Patras, P.O. Box 13273, GR-265 04 Rion, Greece c Institute of Radioisotopes and Radiodiagnostic Products, National Center of Scientific Research “Demokritos”, P.O. 60228, 153 10 Agia Paraskevi, Athens, Greece article info Article history: Received 16 April 2010 Received in revised form 10 June 2010 Accepted 16 June 2010 Keywords: Drug release Molecular imaging Small animal imaging SPECT PET Radiolabeled nanoparticles Angiogenesis abstract Small animal molecular imaging is a rapidly expanding efficient tool to study biological processes non- invasively. The use of radiolabeled tracers provides non-destructive, imaging information, allowing time related phenomena to be repeatedly studied in a single animal. In the last decade there has been an enormous progress in related technologies and a number of dedicated imaging systems overcome the limitations that the size of small animal possesses. On the other hand, nanoparticles (NPs) gain increased interest, due to their unique properties, which make them perfect candidates for biological applications. Over the past 5 years the two fields seem to cross more and more often; radiolabeled NPs have been assessed in numerous pre-clinical studies that range from oncology, till HIV treatment. In this article the current status in the tools, applications and trends of radiolabeled NPs reviewed. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Over the past century imaging became a tool that changed the way medicine thinks and practices, mainly for diagnostic purposes and over the past 20 years for therapeutic as well. X-rays gave for the first time the opportunity to obtain information for body’s inte- rior, with non-invasive methods. As technology evolved in physics, engineering and computer technology, new physical principles were exploited, resulting to new imaging tools that provided dif- ferent types of information. Starting from simple planar anatomical information, three-dimensional functional information can be now obtained and molecular imaging (MI) promises to provide (and in many cases already provides) in vivo information about proteins, genes, molecules, stem cells; thus mechanisms related to biologi- cal processes and diseases can be studied, with significant benefits, compared to in vitro and ex vivo studies [1–3]. Having a quick look in medical imaging progress, we can notice that the more complicated the physical principles and data acqui- ∗ Corresponding author. Tel.: +30 2610 969146; fax: +30 2610 969172. E-mail addresses: gloudos@teiath.gr (G. Loudos), gkagad@gmail.com, George.Kagadis@med.upatras.gr (G.C. Kagadis), dpsimad@chem.uoa.gr (D. Psimadas). URLs: http://www.teiath.gr/stef/tio/ni (G. Loudos), http://www.kagadis.gr (G.C. Kagadis). 1 Tel.: +30 210 5385375; fax: +30 210 5385302. 2 Tel.: +30 210 6503683. sition techniques are the more valuable the obtained information becomes. To explain this statement a simple example is provided: (i) X-ray imaging is based on the idea that X-ray photons pass through the body, they are attenuated and a detector measures the total attenuation in the body; thus providing a two-dimensional image of the anatomical attenuation map. (ii) Single photon emis- sion computed tomography (SPECT) is based on the idea that a radiopharmaceutical is injected in the body and concentrates in an organ or structure of interest. Radiopharmaceutical carries an iso- tope (or even more); the emitted photons pass through a collimator and the detector produces a two-dimensional image of radiophar- maceutical’s distribution, which depends on target’s functionality. It must be noted here that the disadvantage of using a collima- tor is the significant reduction in sensitivity. (iii) Positron emission tomography (PET) is based on a similar principle, but the radio- pharmaceuticals used emit positrons; a positron is annihilated in a distance of 1–4 mm from each emission point and two oppo- site travelling photons are produced. The detector needs to be able to simultaneously detect those two photons, and a reconstruction algorithm is necessary to obtain the three-dimensional distribution for radiopharmaceuticals concentration. Very recently the intro- duction of fast electronics [4] allows time information of the two photons to be obtained, thus the annihilation point can be esti- mated with better accuracy; theoretically, further improvement in electronics timing would make reconstruction unnecessary. It is very possible that other physical processes can lead to more excit- ing imaging options in the future. 0720-048X/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2010.06.025