Mapping intra-tumoral heterogeneity in adolescent CNS tumors using simultaneous amide proton transfer (APT)-weighted signal and 18F-choline PET: a feasibility study
Abstract
Paediatric and adolescent gliomas and glioneuronal tumors remain challenging to assess non-invasively. Amide proton transfer (APT) chemical exchange saturation transfer (CEST) MRI has shown promise in adult gliomas but has not been well studied in younger patients. We conducted a feasibility study to assess whether APT-weighted signal can act as a non-invasive surrogate of tumor proliferation in adolescent CNS tumors by correlating it with 18F-choline PET uptake (SUV) as a proxy for membrane synthesis/ proliferative activity. Ten adolescent patients (14–19 yrs), seven with histologically confirmed and three with radiologically suspected CNS tumors, underwent simultaneous APT CEST and 18F-choline PET-MRI. Regions of interest (ROIs) corresponding to non-enhancing, enhancing, necrotic tumor, and contralateral white matter were delineated. Mean APT-weighted signal intensity (SI) and PET SUV were extracted per ROI. Nonparametric statistics and Spearman’s correlation analyses were performed. APT-weighted signal was significantly elevated in enhancing, non-enhancing, and necrotic tumor ROIs compared to normal white matter (p < 0.001). 18F-choline SUV was elevated in enhancing and necrotic ROIs vs white matter, but not significantly so for non-enhancing tumor (p = 0.02). A correlation between enhancing and whole-tumor APT-weighted signal and 18F-choline SUV was seen (p < 0.001). This pilot feasibility study demonstrates that APT-CEST MRI is technically feasible in adolescents with CNS tumors and that APT-weighted signal may reflect tumour metabolic activity. The findings are hypothesis-generating and require validation in larger, histologically homogeneous cohorts. The detection of elevated APT-weighted signal even in non-enhancing tumor regions suggests potential utility in monitoring non-contrast-enhancing disease. Larger cohorts and multimodal correlation (e.g. Ki-67, amino acid PET) are warranted to confirm and extend these findings.