μmr 588

The r₁ and r₂ relaxivities of SPIO@PEG-GdDTPA were measured on a 1.5 T clinical MRI scanner system (μMR 588, United Imaging Healthcare) and a 3.0 T clinical MRI scanner system (Signa Architect, GE Medical systems) using the head RF coils. The samples were dispersed in deionized water with different paramagnetic metal ion concentrations at 0.5, 0.4, 0.3, 0.25, 0.15, 0.1, 0.06 and 0.03 (Fe + Gd) mM. Subsequently, longitudinal and transverse relaxation rates (the reciprocal of relaxation times) were, respectively, measured and used for calculating corresponding relaxivity by seeking the slopes of best fit lines of relaxation rates versus metal ion concentrations. T₁- and T₂-weighted MR images in vitro were acquired with a conventional SE sequence by the following parameters: T₁-weighted images at 1.5 T (TE = 12.2 ms, TR = 125 ms, slice thickness = 3 mm, field of view = 200 × 120 mm, flip angle = 90°); T₂-weighted images at 1.5 T (TE = 18 ms, TR = 3500 ms, slice thickness = 3 mm, field of view = 200 × 120 mm, flip angle = 90°).

Fourier transform infrared (FTIR) spectra were delineated on a Perkin-Elmer spectrophotometer in the region of 4000–400 cm⁻¹ with a powder sample on a KBr plate. X-ray diffraction (XRD) patterns were collected on a Dandong Fangyuan DX-1000 diffractometer (Haoyuan Instrument, China) with a Cu Kα radiation source (λ = 1.5418 Å) in the 2θ range 20–80^°. Thermogravimetric analysis of all samples was performed on NETZSCH TG209F1 Thermogravimetric Analyzer (NETZSCH Scientific Instruments Trading Ltd, Germany). Elemental analyses were performed by energy-dispersive spectrometer (EDS) on INCAPentaFETx3 (Oxford Instruments, UK). The size distribution and morphology of all samples were investigated by TEM (Tecnai G2 F20 S-TWIN, FEI), for which 10 µl of the samples were dried on a copper grid. The hydration diameter and zeta potential of all samples were tested by DLS on a Malvern Nanosizer (Zetasizer Nano ZS, UK). Iron and gadolinium concentration of all samples were evaluated by elemental analysis using an atomic absorption spectroscopy (AA800, Perkin-Elmer, USA). T₁ and T₂ relaxivities were recorded and calculated on a 1.5 T (μMR 588, United Imaging Healthcare, PRC) and 3.0 T clinical MRI scanner (Signa Architect, GE Medical systems, USA) at room temperature.