Abstract
Developing multimodal contrast agents is an upcoming area and hydroxyapatite nanoparticles substituted with various elements like gadolinium, eurobium etc., seems to be a promising contrast agent, especially for multimodal imaging of bone-tissue interface. A bimodal contrast agent using silver (Ag+) and gadolinium (Gd3+) ions co-substituted hydroxyapatite nanoparticles has been developed for X-ray and magnetic resonance imaging. Ag+ and Gd3+ ions were co-substituted into hydroxyapatite at various atomic percentages (Ag:Gd=0.25:0.25, 0.25:0.5, 0.25:0.75) using microwave accelerated wet chemical synthesis. Pure as well as Ag+ and Gd3+ ions substituted hydroxyapatite samples were also synthesized for comparison. All samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy etc., and found to be monophasic, nanocrystalline with the substituted ions. These co-substituted hydroxyapatite samples were then tested in different diagnostic modalities such as X-ray, computed tomography imaging and magnetic resonance imaging. Appreciable variation in contrast was observed with different amount of substitutions. All the Ag+ and Gd3+ ions co-substituted hydroxyapatite nanoparticles showed higher contrast in all imaging modalities compared to those substituted with either Ag+ or Gd3+ ions only. Hydroxyapatite sample co-substituted with 0.25Ag and 0.75Gd at. % substitution showed the best bimodal CT-MRI contrast.
Highlights
Various non-invasive imaging modalities such as computed X-ray tomography (CT), magnetic resonance imaging (MRI), ultrasound imaging (USI), positron emission tomography (PET) and single photon emission spectroscopy (SPECT) are used in the diagnosis of various diseases [1,2]
A single imaging technique does not give a complete perspective on all aspects of a disease/disorder, it is common in clinical practice to rely on two or more techniques to arrive at an accurate and reliable diagnosis
Only separate contrast agents are used for each imaging mode like iodine or barium compounds as radio contrast agents for X-ray/CT imaging, paramagnetic Gd3+ compounds and super paramagnetic iron oxide (SPIO) nanoparticles for MR imaging [3]
Summary
Various non-invasive imaging modalities such as computed X-ray tomography (CT), magnetic resonance imaging (MRI), ultrasound imaging (USI), positron emission tomography (PET) and single photon emission spectroscopy (SPECT) are used in the diagnosis of various diseases [1,2]. Studies are being carried out to combine different modes of imaging by developing a single contrast agent based on polymers, liposomes and inorganic nanoparticles like hydroxyapatite (HA) [3,4]. Multimodal contrast agents based on inorganic nanoparticles have attracted considerable attention due to their small tunable size and attractive physical and chemical properties including bio-functionalization, prolonged circulating half-life, passive accumulation at tumor site through enhanced permeation and retention (EPR) effect [5]. The nanoparticulate contrast agents have been reported to provide enhanced signal sensitivity and impart information at the cellular levels [7]
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