Mapping intra-tumoural heterogeneity in a spectrum of adolescent central nervous system tumours using APT-CEST and 18F-choline PET-MRI

Abstract

Background: Paediatric and adolescent gliomas and glioneuronal tumours 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. Purpose: To assess whether APT CEST signal can act as a non invasive surrogate of tumour proliferation in adolescent CNS tumours by correlating it with 18F choline PET uptake (SUV) as a proxy for membrane synthesis / proliferative activity. Methods: Ten adolescent patients (14 to 19 yrs) with confirmed or suspected gliomas / glioneuronal tumours underwent simultaneous APT CEST and 18F choline PET MRI. Regions of interest (ROIs) corresponding to non enhancing, enhancing, necrotic tumour, and contralateral white matter were delineated. Mean APT signal intensity (SI) and PET SUV were extracted per ROI. Nonparametric statistics and Spearmans correlation analyses were performed. Results: APT SI was significantly elevated in enhancing, non enhancing, and necrotic tumour 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 tumour (p=0.02). A strong correlation between whole tumour APT SI and 18F choline SUV was seen (Spearman r=0.86, p<0.001). Conclusion: Our results indicate that APT CEST is feasible in adolescents and may reflect proliferative tumour burden. The detection of elevated APT SI even in non enhancing tumour 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.

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