Nuclear Overhauser enhancement imaging at −1.6 ppm in rat brain at 4.7T

Abstract

AbstractPurposeA new nuclear Overhauser enhancement (NOE)‐mediated saturation transfer signal at around −1.6 ppm, termed NOE(−1.6), has been reported at high fields of 7T and 9.4T previously. This study aims to validate the presence of this signal at a relatively low field of 4.7T and evaluate its variations in different brain regions and tumors.MethodsRats were injected with monocrystalline iron oxide nanoparticles to reduce the NOE(−1.6) signal. CEST signals were measured using different saturation powers before and after injection to assess the presence of this signal. Multiple‐pool Lorentzian fits, with/without inclusion of the NOE(−1.6) pool, were performed on CEST Z‐spectra obtained from healthy rat brains and rats with 9L tumors. These fits aimed to further validate the presence of the NOE(−1.6) signal and quantify its amplitude.ResultsThe NOE(−1.6) signal exhibited a dramatic change following the injection of monocrystalline iron oxide nanoparticles, confirming its presence at 4.7T. The NOE(−1.6) signal reached its peak at a saturation power of ∼0.75 μT, indicating an optimized power level. The multiple‐pool Lorentzian fit without the NOE(−1.6) pool showed higher residuals around −1.6 ppm compared to the fit with this pool, further supporting the presence of this signal. The NOE(−1.6) signal did not exhibit significant variation in the corpus callosum and caudate putamen regions, but it showed a significant decrease in tumors, which aligns with previous findings at 9.4T.ConclusionThis study successfully demonstrated the presence of the NOE(−1.6) signal at 4.7T, which provides valuable insights into its potential applications at lower field strengths.