Assessment of Amide Proton Transfer and Nuclear Overhauser Effects using long RF Saturation at 3T in Clinical Brain Tumor Applications

MTR _asym can be robustly and efficiently measured in clinical settings, including 3D acquisitions with large coverage in less than 5 minutes. On the other hand, MTR _asym as a measure for APT signal levels, was previously reported to be biased by Nuclear Overhauser effects (NOE) at opposite frequency offsets. The influence of NOE effects may strongly depend on the main magnetic field (B ₀ ) and on saturation parameters. Most reported studies were performed at ultra-high B ₀ 7T and typically employed short RF saturation (T _sat <1s) and low saturation field amplitudes (e.g. B _1,rms =0.5 T). In this study, a previously proposed APT protocol (Tsat=2s; B _1,rms =2 T) on 3.0T MRI systems is applied for human brain tumor cases and analyzed for NOE contributions using improved Z-spectral fitting methods. It was hypothesized, that there is only a small or negligible NOE contrast between NAWM and tumor tissue using long saturation pulses at 3T. The study results indicate that MTR _asym in combination with a specific protocol at 3T could be used to assess APT signal levels in clinical applications without significant interference of NOE effects.

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