Whole-Brain Amide Proton Transfer (APT) and Nuclear Overhauser Enhancement (NOE) Imaging in Glioma Patients Using Low-Power Steady-State Pulsed Chemical Exchange Saturation Transfer (CEST) Imaging at 7T

Purpose: To explore the relationship of amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) signal intensities with respect to different World Health Organization (WHO) brain tumor grades (II to IV) at 7T. Materials and Methods: APT-based and NOE-based signals at 7T using low-power steady-state chemical exchange saturation transfer (CEST) were compared among de novo primary gliomas of different WHO grades (II to IV). The quantitative APT and NOE signals, calculated by fitting approach using extrapolated semisolid MT reference (EMR) signals, were compared with the magnetization transfer ratio asymmetry (MTRasym) analysis, commonly used in APT-weighted MRI. Results: The observed NOE signals of all glioma grades were significantly lower than normal brain tissue (P < 0.01). NOE signals significantly differed between low-grade (II) gliomas and high-grade (III, IV) gliomas (P < 0.05). APT signals showed no difference between the tumor regions for any glioma grades (M53.08%, 2.64%, and 3.10%, 95% confidence interval [CI] 52.81% similar to 3.33%, 2.36% similar to 2.91%, and 2.85% similar to 3.36% for grade II, III, and IV, respectively), and between normal brain tissue and all glioma grades (P50.08, M54.29% and 2.94%, 95% CI53.57% similar to 4.99% and 2.47% similar to 3.41% for normal and average grade II, III, and IV), while MTRasym differed significantly between normal tissue and all glioma grades (P < 0.05). Conclusion: NOE contributes substantially to APT-weighted MRI at 7T at low RF saturation power and provides a promising biomarker for glioma grading.