Over the years, external beam radiotherapy (EBRT) has been used in the treatment management of many malignancies, including head and neck squamous cell carcinomas (HNSCC). Hypoxia is a common feature in HNSCC. Hypoxic segments in HNSCC have proven to be more resistant to radiotherapy. The ability to identify hypoxia using SPECT and PET tracers has been investigated since the late 1970s. Nitroimidazole-based compounds labelled with positron emitters have been developed to more specifically image hypoxia. This article reviews the current data from research publications on(18)F-FMISO, (18)F-FAZA, (18)F-EF5 and (64)Cu-ATSM.