Kinetics of 13N-ammonia incorporation in human tumours

After intravenous injection of N-labelled ammonia time–activity curves were obtained in a series of malignant neoplasms in man from serial cross-sectional scans through the tumour, using positron emission tomography. Low noise images with virtually no artefacts were obtained using a maximum likelihood reconstruction technique. Tracer concentration was expressed as a fraction of the injected dose ml of tumour tissue.In a first group (eight observations) maximum activity [0.9 to 5.2 (mean3.3)x10 of administered dose ml of tumour tissue] was attained approximately 1 to 3 min post injection. This peak was followed by a clearance phase with a half-time varying between 28.3 and 112 (mean73.1) min. In a second group (of six cases) after an initial rapid rise of the activity, no clearance was detectable during the time of observation, tracer concentration remaining in plateau or even continuing to rise slightly. Maximum activity in this group ranged from 1.1 to 5.3 (mean2.6)x10 of the administered dose ml of tissue. So far no relation has been established between the height and/or shape of the NH3 time–activity curve and a particular tumour type.