References for this review were selected through searches of PubMed with the terms “glioma” or “brain tumour”, in combination with “positron” or “magnetic resonance”. We selected the most original, relevant, and recent papers. Articles identified through searches of the references of articles and the authors' own files were also included. Only papers in English were included. The final list reflects papers relevant to the topics covered in the review.
ReviewMetabolic and molecular imaging in neuro-oncology
Introduction
Introduced in 1977, 18F-labelled 2-fluoro-2-deoxy-D-glucose (FDG) is now in wide clinical use in human beings,1 and more positron-labelled tracers are being used for quantitative in vivo metabolic imaging with PET. These techniques have been complemented by magnetic resonance spectroscopy (MRS), which has given insight into the main endogenous substrates of energy and intermediary metabolism,2 and newer experimental techniques have provided methods for the imaging of gene expression and other specific molecular processes.3 Experimental MRI and optical imaging methods can also be used to image molecular processes, although their application to human metabolic and molecular imaging is restricted, and PET is still predominant.4 New MRI methods for the imaging of brain perfusion and water diffusion provide insights into the metabolic and molecular changes seen in brain tumours.5 The translation of these advances in diagnostic imaging into improvements in therapy and outcome for patients with glioma is a challenge. In this review, we summarise the available metabolic and molecular tracer techniques in this context.
Section snippets
Tomographic imaging methods
Tomographic methods can be used to image diverse physiological and structural targets (figure 1). Modern, multislice CT systems can image the brain in 1–2 seconds, and enhancement with conventional iodinated contrast media can generate dynamic data for functional images, particularly for the measurement of blood flow. MRI also enables the use of dynamic contrast-enhanced techniques for blood flow measurement and provides opportunities to study other contrast mechanisms, such as fluid flow, free
Tumour grading
The WHO scheme for grading tumours is widely accepted,10 and four histological grades have prognostic relevance in brain tumours. Grade I tumours, such as most meningiomas and neurinomas or schwannomas, are the most likely to be cured after macroscopic removal. Grade II tumours, such as astrocytomas and oligodendrogliomas, are classified as low grade because of their low proliferation rates and lack of histological features of malignancy. However, these tumours infiltrate healthy brain tissue
Identification of lesion type
Definitive diagnosis of lesion type usually requires histopathological examination of the tissue. Although metabolic and molecular imaging methods are macroscopic techniques and cannot replace microscopic examination of the tissues, the indicators of tumour vascularity, metabolism, invasiveness, and malignancy provided by these techniques can improve the likelihood of making a correct diagnosis.
All imaging modalities help to distinguish between tumours and non-tumorous lesions.
Tumour extent and infiltration
The extent of solid malignant tumours and benign tumours, such as meningiomas, which lack an intact blood–brain barrier, is usually assessed by the extent of contrast enhancement on CT or MRI. The accurate definition of tumour boundries is more difficult for low-grade gliomas, and many high-grade gliomas are heterogeneous and include regions that do not show contrast enhancement. Another problem is infiltration of normal brain tissue by gliomas, which causes their recurrence and commonly
Response to therapy
Oncological therapy typically aims to change the perfusion or molecular processes of tumours to achieve regression. Metabolic and molecular imaging can be used to monitor many of these targets directly and thus guide therapy and provide direct measures of therapeutic success.
Experimental molecular imaging
Directly imaging tumour components, such as cell surface markers or tumour products, might help to identify potential therapeutic targets that can be used to select individualised treatments. Endothelial growth factors are of particular interest because they mediate the interaction between tumours and their environments, to promote endothelial proliferation and angiogenesis. Vascular endothelial growth factor and endothelial growth factor are potential targets for antiangiogenic treatments.
Summary and perspectives
Many metabolic and molecular imaging techniques are now available for clinical use but their influence on clinical research and diagnostic practice is limited. Most studies cited in this review, although having the potential to improve our understanding of the pathophysiology of disease and to contribute to therapeutic progress, are based on selected clinical case series, which are commonly collected retrospectively. The choice of method depends on locally available technology, technical
Search strategy and selection criteria
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Cited by (89)
Simultaneous dynamic glucose-enhanced (DGE) MRI and fiber photometry measurements of glucose in the healthy mouse brain
2023, NeuroImageCitation Excerpt :Tomographic techniques such as Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET) and Computed Tomography (CT) are widely used in clinical settings to probe brain physiology and pathology. Their strength resides in the possibility to rapidly investigate large volumes at substantial depths in a non-invasive way, allowing for the diagnosis of pathological tissue alterations or the identification of brain areas responsible for specific functions (Herholz et al., 2007; Langen et al., 2017). However, the spatial resolution is limited to the sub-millimeter range even with state-of-the-art technologies (Weiskopf et al., 2021), preventing cell identification and assessment of cell specific contributions to signals.
Lower Grade Gliomas: Relationships Between Metabolic and Structural Imaging with Grading and Molecular Factors
2019, World NeurosurgeryCitation Excerpt :In particular, IDH status and 1p/19q codeletion have been shown to capture the biologic characteristics of LGGs with greater sensitivity compared with histological classification alone,29 which can be hampered by both interobserver variability and sampling errors during surgery. PET with radiolabeled amino acids, such as 11C-METH, has been proved to be a valuable tool for the in vivo characterization of primary brain tumors.30 11C-METH PET can discriminate high- and low-grade gliomas,7-11 provide prognostic information before surgery,12-15,31 and be used for radiation therapy planning.16,17
Brain Tumors
2017, PET/CT in Cancer: An Interdisciplinary Approach to Individualized Imaging