CXCR4 and glioblastoma: Comparative studies will be required to assess the merits of Me-4FDG relative to other carbon-11 and fluorine-18 PET probes, such as amino acids (e.g. [C-11]methionine, [F-18]FDOPA, [F-18]FET, [F-18]fluciclovine [12–14]), or other targets expressed in glioblastomas (e.g. PSMA, CXCR4 [15–17]).