MRI and PET of Brain Tumor Neuroinflammation in the Era of Immunotherapy, From the AJR Special Series on Inflammation.

With the emergence of immune-modulating therapies, brain tumors present important diagnostic imaging challenges. These challenges include planning personalized treatment and adjudicating accurate monitoring approaches and therapeutically specific response criteria. The challenges have been due, in part reliance on nonspecific imaging metrics, such as gadolinium contrast-enhanced MRI or FDG PET, and rapidly evolving biologic understanding of neuroinflammation. The importance of the tumor immune interaction and ability to therapeutically augment inflammation to improve clinical outcomes make it necessary for radiologists to develop a working knowledge of the immune system and its role in clinical neuroimaging. The purpose of this article is to review relevant biologic concepts of the tumor microenvironment of primary and metastatic brain tumors, the interactions between the tumors and the immune system, and MRI and PET methods for imaging inflammatory elements associated with these malignancies. In recognition of the growing fields of immunotherapeutics and precision oncology, clinically translatable imaging metrics for the diagnosis and monitoring of brain tumor neuroinflammation are highlighted. Practical guidance is provided for implementing iron nanoparticle imaging, including imaging indications, protocols, interpretation, and pitfalls. A comprehensive understanding of the inflammatory mechanisms within brain tumors and their imaging features will facilitate the development of innovative noninvasive prognostic and predictive imaging strategies for precision oncology.