A mobile facility for in vivo total body nitrogen analysis

The measurement of nitrogen in vivo can be used as an indication of total protein and is potentially a valuable parameter in diseases where an assessment of nutritional status is of value, such as wasting, gastrointestinal disorders, trauma and cancer. In vivo neutron activation analysis is a technique which enables such a measurement to be made with useful precision. Often however, the specialised facilities necessary are so distant from the medical unit or hospital that the measurement of very ill patients unable to travel far is precluded precisely at times when the data would be of greatest value. In an effort to overcome this difficulty a mobile facility for the determination of nitrogen which can be positioned near to the patient care accommodation has been designed. Developed from an existing high sensitivity mobile whole body counter as a result of a feasibilty study, the facility consists of two radioactive neutron sources (2 x 185 GBq 241-Am-Be) arranged to irradiate the supine patient laterally, while the prompt capture gamma-rays from nitrogen are observed simultaneously with a large NaI (Tl) detector. In order to be as undemanding as possible, the examination involves only a low radiation dose and takes approximately 20 minutes, during which time the patient is scanned slowly from head to feet beneath the detector. In the paper, the design, calibration and performance of the newly constructed apparatus are described together with the results of inital in vivo measurements and an indication of potential applications. (Author)