Effect of Inversion Time on the Linear Correlation between Polyethylene Glycol Coated Iron Oxide Nanoparticles Concentration and Signal Intensity in Inversion Recovery MRI Pulse Sequence

Background and In MRI the concentration of contrast agent is indirectly measured from signal intensity (SI). It is important to find the maximum linear relationship between SI and concentration of the iron oxide nanoparticles for perfusion measurement. The aim of this study was to investigate the effect of inversion time on SI and the maximum linear relationship between SI and concentration of the polyethylene glycol (PEG) coated iron oxide nanoparticles at different inversion times (TIs) using inversion recovery pulse sequence in T1-weighted MR images. A phantom was designed to hold the vials with different concentrations of the PEG coated iron oxide nanoparticles in MRI coil. MR imaging was performed using inversion recovery Turbo-FLASH sequence with different TIs. The maximum SI and the maximum linear relationship between SI and concentration of the nanoparticles were measured at different TIs. The maximum SI and the maximum linear relationship between SI and nanoparticles’ concentration were dependent on TI. The maximum SI at different TIs was seen at the highest concentration (500µmolFe/L). The maximum SI which led to a linear relationship with the nanoparticles concentration (R2=0.99) was obtained up to 105.49 and 243.64µmolFe/L for TIs of 400 and 240ms, respectively. TI has an effect on strength of SI in MRI. Increasing the TI values leads to a decrease in concentration of the PEG coated iron oxide nanoparticles that gives the maximum linear SI.