MRI of tumor-bearing mice

An MRI scanner at 7.4-T field strength was used for MRI studies. A multiecho fast spin–echo sequence was used to simultaneously collect a series of datapoints at different echo times (TE = 15−90 ms with an increment of 15 ms). T2 relaxation time was then calculated by fitting the decay curve on a pixel-by-pixel basis by using a nonlinear monoexponential algorithm M(TE) = M₀ exp(-TE_i/T2), where TE is the echo time, and M(TE) is the MRI signal intensity at which TE is used. Mice were placed in a volume coil and anesthetized using 2% isoflurane throughout the MRI experiments. Tumor-bearing BALB/c mice were scanned to collect contrast-enhanced MRI data 24 h after systemic administration of IONPs at a dose of 20 mg Fe/Kg mouse bodyweight or PBS as a control. A T2 weighted fast spin echo sequence was used to obtain T2 relaxometry of the tumor tissues.