Amine‐weighted chemical exchange saturation transfer magnetic resonance imaging in brain tumors

Amine‐weighted chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is particularly valuable as an amine‐ and pH‐sensitive imaging technique in brain tumors, targeting the intrinsically high concentration of amino acids with exchangeable amine protons and reduced extracellular pH in brain tumors. Amine‐weighted CEST MRI contrast is dependent on the glioma genotype, likely related to differences in degree of malignancy and metabolic behavior. Amine‐weighted CEST MRI may provide complementary value to anatomic imaging in conventional and exploratory therapies in brain tumors, including chemoradiation, antiangiogenic therapies, and immunotherapies. Continual improvement and clinical testing of amine‐weighted CEST MRI has the potential to greatly impact patients with brain tumors by understanding vulnerabilities in the tumor microenvironment that may be therapeutically exploited. Acidification of the brain tumor microenvironment leads to numerous changes within the tumor (A). Our institution's amine‐weighted CEST MRI protocol depends on a "perfect storm" of elevated amino acids, increased T2 relaxation, and a decreased pH, which occurs naturally in brain tumors (B). Biopsy data shows that amine‐weighted CEST contrast correlates with glycolytic function (C). Successful treatment, including immunotherapies (D/E), results in normalization of the acidic microenvironment.