Introduction
Neuroimaging techniques are crucial tools for diagnosing, staging, and monitoring the treatment effects in patients with brain cancers [1]. Structural magnetic resonance imaging (MRI) helps to identify, classify, and grade brain tumors, as well as to guide surgery [2]. Complementary information is obtained with positron emission tomography (PET) imaging, where insights on tissue metabolism can be evaluated, which is particularly valuable for the measurement of fast cell proliferation in tumors and investigation of early-stage tumors [3-6].
Despite the current efficiency of these imaging techniques in brain tumor detection, some limitations remain to be overcome. For example, differentiating among relapsed brain tumors, solitary brain metastases, and inflammatory and necrotic lesions resulting from chemo- and radiotherapy remains a challenge. For example, the most commonly used PET probe for tumor imaging is 2-Deoxy-2-18F-fluoro-D-glucose (FDG), which is actively transported into cells via glucose transporters (GLUTs), accumulating not only in tumor tissue, which contains inflammatory processes itself, but also in other inflamed areas, where glucose metabolism is crucial for neuroinflammatory and neuroimmune responses. This can lead to false positive results for tumor diagnosis [7-9]. Also, both tumors and metastatic sites can display MRI patterns featuring peritumoral hyperintensities with similar intratumoral texture, thus representing a potential confounder for neuroradiologists [10]. In this review, we will discuss selected recent advances in imaging approaches aimed at improving the evaluation of brain tumors and brain metastases in relation to immunomodulation and neuroinflammatory processes. We will focus specifically on one type of brain tumor, glioblastoma (GBM), given that it represents the most aggressive primary malignant brain cancer in adults.