Positron emission tomography and magnetic resonance spectroscopy in cerebral gliomas

Abstract

Purpose

Conventional MRI, the gold standard in structural brain imaging, alone has its limitations in pre-operative tumour grading, biopsy targeting, determination of accurate tumour margins prior to surgical resection/radiation therapy, detection of tumour recurrence and determination of early therapeutic response. The aim was to introduce and review two of the recently most discussed adjunct modalities for molecular imaging in glioma: PET and MRS, and the combination of both.

Methods

A PubMed search with a combination of the terms “MRS”, “glioma” and “glioblastoma”, “brain tumour”, “positron emission” and “PET” was carried out. These results were complemented with a search of the authors’ own files. Preclinical in vitro studies as well as animal studies were excluded.

Results

Published single modality data show that ¹H-MRS and PET perform similarly in answering clinical questions, which cannot be adequately answered by conventional MR imaging alone. Original articles including patients with gliomas and combining the PET and MRS modalities within the same study were scarce and resulted in 17 research papers. These articles especially point to a spatial correlation between ¹H-MRS metabolic ratios and amino acid uptake and a positive relationship with histologically proven cell proliferation markers, indicating diagnostic improvement in the differentiation between glioma and benign lesions, in the delineation of brain tumours and in the differentiation between treatment-related changes and tumour progression.

Conclusion

PET and ¹H-MRS have shown their value in the non-invasive diagnosis of gliomas delivering metabolic tumour information in addition to pure structural information from conventional MRI or CT alone. The very few studies, which were conducted evaluating ¹H-MRS and PET in combination, indicate a diagnostic benefit from a combined imaging approach in glioma and encourage more systematic investigation—ideally carried out in multicentric settings, in experienced neuroimaging centres (with access to integrated PET/MRI scanners), using standardized imaging- and analysis protocols.

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