Dynamic mapping of amphetamine response in the rat brain using bold and iron techniques

Conventional blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) has been wildly used in neuroscience studies. Even though the BOLD method offers the functional information, the low signal-to-noise ratio could not provide an activated brain area accurately and the signal could not be easily inspected from the complicated neuronal interactions. In this regard, the present study aims to use an ultra-small super-paramagnetic iron oxide (USPIO) nanoparticle coated with covalently bound bifunctional poly(ethylene glycol) polymers to enhance the brain functional responses by the IRON (increased relaxation with iron oxide nanoparticles) technique. The R₁ and R₂ of this USPIO were 53.6 mMsec^-1 and 359.8 mMsec^-1, respectively, and both were higher than most of the commercial products under 0.47 T nuclear magnetic resonance measurement. In this study, the time activity curves in responsive brain areas were evaluated following USPIO injection (3 mg of Fe/kg). The amphetamine (2 mg/kg) was used as a functional stimulator to reveal the changes of relative cerebral blood volume in different brain areas. All imaging experiments were performed by Bruker Biospec BMT 47/40 4.7 T MRI system. The results show that, compared to the BOLD signals; significant event related responses were observed in striatum, insular cortex, nucleus accumbens, somatosensory cortices, and lateral thalamus using the IRON technique. Furthermore, the usability of this USPIO in detecting rCBV responses was confirmed by comparing with previous researches.