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Abstract
Despite its good resolution, magnetic resonance imaging intrinsically has low sensitivity. Recently, contrast agent nanoparticles have been used as sensitivity and contrast enhancer. The aim of this study was to investigate a new controlled synthesis method for gadolinium oxide-based nanoparticle preparation. For this purpose, diethyleneglycol coating of gadolinium oxide (Gd2O3-DEG) was performed using new supervised polyol route, and small particulate gadolinium oxide (SPGO) PEGylation was obtained with methoxy-polyethylene-glycol-silane (550 and 2,000 Da) coatings as SPGO-mPEG-silane550 and 2,000, respectively. Physicochemical characterization and magnetic properties of these three contrast agents in comparison with conventional Gd-DTPA were verified by dynamic light scattering transmission electron microscopy, Fourier transform infrared spectroscopy, inductively coupled plasma, X-ray diffraction, vibrating sample magnetometer, and the signal intensity and relaxivity measurements were performed using 1.5-T MRI scanner.As a result, the nanoparticle sizes of Gd2O3-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000 could be reached to 5.9, 51.3, 194.2 nm, respectively. The image signal intensity and longitudinal (r1) and transverse relaxivity (r2) measurements in different concentrations (0.3 to approximately 2.5 mM), revealed the r2/r1 ratios of 1.13, 0.89, 33.34, and 33.72 for Gd-DTPA, Gd2O3-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000, respectively.The achievement of new synthesis route of Gd2O3-DEG resulted in lower r2/r1 ratio for Gd2O3-DEG than Gd-DTPA and other previous synthesized methods by this and other groups. The smaller r2/r1 ratios of two PEGylated-SPGO contrast agents in our study in comparison with r2/r1 ratio of previous PEGylation (r2/r1 = 81.9 for mPEG-silane 6,000 MW) showed that these new three introduced contrast agents could potentially be proper contrast enhancers for cellular and molecular MR imaging.
Highlights
Magnetic resonance imaging (MRI) is one of the various techniques used widely as imaging tools in clinical diagnosis
Unlike other two methods of computed tomography (CT) and positron emission tomography (PET), MRI has no ionizing radiation, while, with same spatial resolution (SR) as CT, having a high SR of 0.2 to 0.3 mm compared to 3 mm of PET scan [1,2]
Gd3+ ions are generally used as a positive contrast agent which has seven unpaired electrons and produce a magnetic moment that is significantly stronger than a proton, and its physical properties are suitable for reducing the longitudinal (T1) and transverse (T2) proton relaxation times [6]
Summary
Magnetic resonance imaging (MRI) is one of the various techniques used widely as imaging tools in clinical diagnosis. Imaging contrast depends on signal intensity difference between two adjacent tissues or areas. Contrast agents can modify the signal intensity in different tissues and enhance intrinsic contrast. These are categorized according to the signal intensity produced on T1- and T2-weighted images: ‘positive’ (high signal intensity) or ‘negative’ (low signal intensity) [4,5]. Gd3+ ions are generally used as a positive contrast agent which has seven unpaired electrons and produce a magnetic moment that is significantly stronger than a proton (nearly 700 times), and its physical properties are suitable for reducing the longitudinal (T1) and transverse (T2) proton relaxation times [6]. The efficiency of the contrast agent is determined by relaxivity (ri) that changes the longitudinal and transverse relaxation times
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