Abstract. The magnetite (Fe3O4) nanoparticles (MNPs) coated with poly(N-vinyl pyrrolidone) (PVP) via covalent bonds were prepared as T2 contrast agent for magnetic resonance imaging (MRI). The surface of MNPs was first coated with 3-(trimethoxysilyl) propyl methacrylate (silan A) by a silanization reaction to introduce reactive vinyl groups onto the surface, then poly(N-vinyl pyrrolidone) was grafted onto the surface of modified-MNPs via surface-initiated radical polymerization. The obtained nanoparticles were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), TEM (transmission electron microscopy), VSM (vibrating sample magnetometer), and TGA (thermogravimetric analysis). The MNPs had an average size of 14 nm and exhibited superparamagnetism and high saturation magnetization at room temperature. T2-weighted MRI images of PVP-grafted MNPs showed that the magnetic resonance signal is enhanced significantly with increasing nanoparticle concentration in water. The r1 and r2 values per millimole Fe, and r2/r1 value of the PVP-grafted MNPs were calculated to be 2.6 , 72.1, and 28.1(mmol/l) -1 ·s -1 , respectively. These results indicate that the PVP-grafted MNPs have great potential for application in MRI as a T2 contrast agent. Vol.4, No.6 (2010) 329-338 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2010.42 region that they are accumulated, and hence cause negative contrast and provide a dark state in the image where the compounds are accumulated [15]. However, the direct use of magnetic nanoparticles as in vivo MRI contrast agent results in biofouling of the particles in blood plasma and formation of aggregates that are quickly sequestered by cells of the reticular endothelial system (RES) such as macrophages [16,17]. Furthermore, aggregated nanoparticles change their superparamagnetic response [7]. Therefore, in order to minimize biofouling and aggregation of particles and escape from the RES for longer circulation times, the nanoparticles are usually coated with a layer of hydrophilic and biocompatible polymer such as dextran [18], dendrimers [19], poly(ethylene glycol) (PEG) [20], and poly(vinyl pyrrolidone) (PVP) [21][22][23]. Of synthetic polymers, PVP is water-soluble, non-charged, non-toxic, and is used in various medical applications [24]. While there is a potential concern about covalent interaction between hydrophilic polymers and magnetic nanoparticles in order to increase their stability in physiological medium [25][26][27][28][29], PVP coating on Fe 3 O 4 nanoparticles in all previous works has been achieved through noncovalent interaction. Now, polymers grafting of magnetic nanoparticles is one of the most attractive methods of surface modification [30,31]. In the present study, we carried out chemical synthesis and characterization of PVP-functionalized magnetite (Fe 3 O 4 ) nanoparticles. Since the PVP was bonded to the surface of magnetite nanoparticles through covalent bonds, the prepared magnetic fluid (ferrofluid) was ve...

The present study was an attempt to investigate the effect of variation of inversion time (T (I)) and saturation time (T (S)) on the linear relationship between contrast agent concentration and signal intensity (SI) on Turbo Fast Low Angle Shot (TurboFLASH) T (1)-weighted images in MRI. For this purpose, inversion recovery (IR) and saturation recovery (SR) sequences (Center out Phase-Encoding acquisition) were used. A phantom was designed to hold 25 vials which contained either different (between 0 and 19.77 mmol/L) or constant (1.20 mmol/L) concentrations of contrast agent. The vials of constant concentration were used for the measurement of coil non-uniformity, which was normalized to give a correction factor. The vials of different concentrations were used to measure the SI by using different sequences and different T (I) and T (S) values. To calculate the corrected SI for different concentrations, we multiplied the SI of each vial by its correction factor. The relationships between the corrected SI and the concentration [were evaluated], where the threshold of (R (2) = 0.95 and 0.99) was maintained. This study shows that different sequences and different T (I) and T (S) values can have an effect on the correlation between the SI and concentration. Regardless of the values of T (I), T (S), and the different IR and SR sequences chosen, the linear relationship between the SI and concentration was about twice that previously reported (i.e., 0.8 mmol/L, R (2) = 0.95).

BackgroundMRI is not able to directly measure the concentration of contrast agent. It is measured indirectly from the signal intensity (SI). It is very important to know how much contrast agent should be injected to receive a maximum SI in the region of interest (ROI).ObjectivesThe aim of this study was to investigate the maximum relationship between contrast concentration and signal intensity (SI) on T1-weighted images using spin echo (SE), fast spin echo (FSE) and inversion recovery (IR) sequences.Materials and MethodsTo assess the relationship between SI and concentration, a water-filled phantom containing vials of different concentrations of gadolinium DTPA (Gd-DTPA) (0 to 19.77 mmol/L) or a constant concentration (1.2 mmol/L) of contrast agent was used. The vials of constant concentration were used to measure coil nonuniformity. The mean SI was obtained in the ROI using T1-weighted images. All studies were carried out using a 0.3 T clinical MR scanner with a standard head coil.ResultsThis study shows that maximum SI will appear at different ranges in different sequences. The maximum SI can be seen at concentrations of 5.95, 4.96 and 3.98mmol/L for SE, FSE and IR, respectively.ConclusionUsing standard imaging parameters, each MRI sequence reaches its maximum SI in a specific contrast concentration, which is highest in SE and least in IR in a comparison between SE, FSE and IR sequences.

Objective: Previous studies have shown that the organ blood flows (OBFs) calculated using the T 1 weighted MRI technique were lower than the expected values. The aim of this study was a flow measurement comparison between the theoretical and experimental flows based on the technique before and after corrections (coil non-uniformity and inflow) using a flow phantom at two different concentrations (0.8 and 1.2 mmol l -1 ). Methods: A flow phantom was designed to produce three different flow rates at the same time. Theoretical flow was calculated by measuring the volumes of the phantom and dividing them by the time taken to fill these volumes. T 1 weighted turbo fast lowangle shot images were used to measure signal intensity (SI) change during the first bolus passage of the contrast medium through the phantom using linear phaseencoding acquisition. Results: The corrected experimental flow based on the technique shows a good agreement with the theoretical flow, where the flow rate is low at the two concentrations. Conclusion: TheT 1 weighted MRI technique after the two correction factors can be used to measure the absolute flow where the flow rate is low, such as in the capillaries. For measuring high flow rate (e.g. artery), additional correction factors should be considered.