Tumoural hypoxia can influence response to radiotherapy and other treatments, and oxygenation status has proved to be a prognostic indicator of the outcome of radiotherapy.1Therefore, it is important to assess tumoural hypoxia and reoxygenation before selection of treatment protocols. During the last two decades, much attention has been paid to noninvasive imaging techniques using radiolabelled markers for the detection of hypoxic cells in solid tumours.2Technetium (99mTc) is a very convenient isotope for use with such imaging because it is readily available and suited to routine clinical use. 99mTc labelled ligands containing 2-nitroimidazole have been recently developed. 99nTc labelled 4, 9-diaza-3, 3, 10,10-tetramethyldodecan-2, 11 -dione dioxime (99mTc-HL91), which lacks the nitroimidazole group,showed even greater hypoxic selectivity.3