Abstract
ObjectiveClinical 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 methodsAPT- and NOE-weighted maps based on Lorentzian difference (LD) and inverse magnetization transfer ratio (MTRREX) were acquired with a 3D snapshot CEST acquisition at 3 T. Saturation power was investigated first by varying B1 (0.5–2 µT) in 5 healthy volunteers then by applying B1 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 (VPhypo/hyper,CEST) in APT/NOE-weighted images were calculated for each patient.ResultsLD APT resulting from using a B1 of 1.5 µT was found to provide significant positive TCtumor,NAWM and MTRREX NOE (B1 of 1.5 µT) provided significant negative TCtumor,NAWM in tissue differentiation. MTRREX-based NOE imaging under 1.5 µT provided significantly larger VPhypo,CEST than MTRREX APT under 1.5 µT.ConclusionThis work showed that with a rapid CEST acquisition using a B1 saturation power of 1.5 µT and covering the whole tumor, analysis of both LD APT and MTRREX NOE allows for observing tumor heterogeneity, which will be beneficial in future studies using CEST-MRI to improve imaging diagnostics for non-enhancing glioma.
Highlights
Chemical exchange saturation transfer (CEST) imaging is a novel MRI technique with great potential for glioma diagnostics
For MTRREX, amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) hypointensity in the tumor region was found, which was stronger when using a B1 of 1.5 μT compared to 0.5 μT
We found that Lorentzian difference (LD) APT with using a B1 saturation power of 1.5 μT provided significant positive T Ctumor,normal appearing white matter (NAWM) and MTRREX NOE with using a B1 of 1.5 μT provided significant negative T Ctumor,NAWM
Summary
Chemical exchange saturation transfer (CEST) imaging is a novel MRI technique with great potential for glioma diagnostics. CEST is sensitive to a reduction of bulk water signal induced by saturation transfer from exchangeable protons in a number of compounds, via which these compounds can be detected [1]. Some of these biological compounds are increased in tumor regions and can potentially be used as biomarkers for tumors. Previous work has shown that APT signal is closely related to increased cell density, proliferation [3,4,5], and concentrations of intracellular proteins in gliosarcoma [6, 7].
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