The development of biomedical imaging techniques, such as computed X-ray tomography (CT), Magnetic Resonance Imaging (MRI), optical imaging, ultrasound, single photon emission computed tomography (SPECT) and positron emission tomography (PET), has provided very useful tools for diagnosis and therapy. These modalities give highly complementary information. For example, PET is a powerful tool for whole body imaging with outstanding detection sensitivity (less than picomolar range), whereas MRI and CT provide high-resolution anatomic information. MRI also permits a spectroscopy (MRS) and functional MRI (fMRI). Thus, it is an ultimate goal to combine two or more imaging modalities providing complementary information, such as morphology and function. Although the combination of PET and CT has already been successfully realized in clinical and preclinical studies, the major limitation is that CT has limited soft-tissue contrast, and need extra dose of radiation. Furthermore, the imaging is performed sequentially rather than simultaneously. So the preferred choices could be combination of the MRI with PET, not only because of the absence of ionizing radiation in MRI but also for its excellent soft-tissue contrast, and its flexible scan protocols. The MRI/PET could create enormous possibilities and provides completely new opportunities to study pathology and biochemical processes in vivo.
To take advantage of high resolution of MRI and the high sensitivity of PET, current researches are focused on the dual modalities imaging contrast agent. However, current approach for labeling magnetic NPs with the radioactive copper ion is through a chelator. Because it is not a covalent bond, the stability of the conjugation is always a severe concern, especially in an in vivo system. In contrast to surface modification, incorporating radioisotope into core of the nanoparticles received highly attention. But resulted iron oxide nanoparticles are rather polydisperse and irregular in shape.
To develop successful MRI nanoparticles, two criteria factors need to be well designed. a) Well controlled size of nanoparticles. b) The surface coating and functionalization. So far, no approaching have been achieved for intrinsitic labeling of MNPs with tunable size and surface modification. To address this problem, we developed a stable dual modalities magnetic NPs by incorporating copper ion into the core of the magnetic NPs with tunable size and surface coating reagents. We will further demonstrate that the nanoparticle can be used for PET-MRI dual modality imaging after doped with radioactive copper.