3D APT and NOE CEST-MRI of healthy volunteers and patients with non-enhancing glioma at 3 T

OBJECTIVE: Clinical application of chemical exchange saturation transfer (CEST) can be performed with investigation of amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) effects. Here, we investigated APT- and NOE-weighted imaging based on advanced CEST metrics to map tumor heterogeneity of non-enhancing glioma at 3 T. MATERIALS AND METHODS: APT- and NOE-weighted maps based on Lorentzian difference (LD) and inverse magnetization transfer ratio (MTR(REX)) were acquired with a 3D snapshot CEST acquisition at 3 T. Saturation power was investigated first by varying B(1) (0.5–2 µT) in 5 healthy volunteers then by applying B(1) of 0.5 and 1.5 µT in 10 patients with non-enhancing glioma. Tissue contrast (TC) and contrast-to-noise ratios (CNR) were calculated between glioma and normal appearing white matter (NAWM) and grey matter, in APT- and NOE-weighted images. Volume percentages of the tumor showing hypo/hyperintensity (VP(hypo/hyper,CEST)) in APT/NOE-weighted images were calculated for each patient. RESULTS: LD APT resulting from using a B(1) of 1.5 µT was found to provide significant positive TC(tumor,NAWM) and MTR(REX) NOE (B(1) of 1.5 µT) provided significant negative TC(tumor,NAWM) in tissue differentiation. MTR(REX)-based NOE imaging under 1.5 µT provided significantly larger VP(hypo,CEST) than MTR(REX) APT under 1.5 µT. CONCLUSION: This work showed that with a rapid CEST acquisition using a B(1) saturation power of 1.5 µT and covering the whole tumor, analysis of both LD APT and MTR(REX) NOE allows for observing tumor heterogeneity, which will be beneficial in future studies using CEST-MRI to improve imaging diagnostics for non-enhancing glioma.