Radiolabeled Nanoparticles for Molecular Imaging

Molecular imaging (MI) comprises non-invasive monitoring of functional and spatiotemporal processes at molecular and cellular levels in humans and other living systems. In contrast to conventional diagnostic imaging, MI seeks to probe the molecular abnormalities that are the basis of disease rather than capture the images of the end effects of the molecular alterations. Imaging techniques such as magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), positron emission tomography (PET) and optical fluorescence imaging (OI) have been used to monitor such processes. Radionuclide-based imaging methods, such as SPECT and PET, use internal radiation that is administered through a target-specific molecule labeled with a radionuclide at doses free of pharmacologic side effects. Nuclear imaging is an established clinical MI modality that, compared to other modalities, offers better sensitivity and has no tissue penetration limits (Massoud & Gamghir, 2003; Ferro-Flores et. al., 2010a). Nuclear technologies have been evolving toward greater sensitivity due to enhanced hardware development, such as multipinhole acquisitions methods or pixelated semiconductor detectors. In parallel with the hardware advances, steady progress is being made in image-processing algorithms, and such algorithms may soon provide substantial reduction in SPECT acquisition times without sacrificing diagnostic quality (Madsen, 2007). The fusion of nuclear and anatomical images from computed tomography (CT) into a single imaging device (SPECT/CT and PET/CT) has been very useful for clinical oncology (Hong et al., 2009a).