Quantitative assessment of amide proton transfer (APT) and nuclear overhauser enhancement (NOE) imaging with extrapolated semisolid magnetization transfer reference (EMR) signals: II. Comparison of three EMR models and application to human brain glioma at 3 Tesla.

PURPOSE: To evaluate the use of three extrapolated semisolid magnetization transfer reference (EMR) methods to quantify amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) signals in human glioma.
METHODS: Eleven patients with high-grade glioma were scanned at 3 Tesla. aEMR(2) (asymmetric magnetization-transfer or MT model to fit two-sided, wide-offset data), sEMR(2) (symmetric MT model to fit two-sided, wide-offset data), and sEMR(1) (symmetric MT model to fit one-sided, wide-offset data) were assessed. ZEMR and experimental data at 3.5 ppm and -3.5 ppm were subtracted to calculate the APT and NOE signals (APT(#) and NOE(#)), respectively.
RESULTS: The aEMR(2) and sEMR(1) models provided quite similar APT(#) signals, while the sEMR(2) provided somewhat lower APT(#) signals. The aEMR(2) had an erroneous NOE(#) quantification. Calculated APT(#) signal intensities of glioma (∼4%), much larger than the values reported previously, were significantly higher than those of edema and normal tissue. Compared with normal tissue, gadolinium-enhancing tumor cores were consistently hyperintense on the APT(#) maps and slightly hypointense on the NOE(#) maps.
CONCLUSION: The sEMR(1) model is the best choice for accurately quantifying APT and NOE signals. The APT-weighted hyperintensity in the tumor was dominated by the APT effect, and the MT asymmetry at 3.5 ppm is a reliable and valid metric for APT imaging of gliomas at 3T.