Of mermaids and mountains. Three decades of prompt activation in vivo.

During 1966 to 1972, several laboratories demonstrated the feasibility of measuring the major body elements H, N, Ca, and Cl by prompt gamma in vivo neutron activation analysis (PGIVNA). The MERMAID facility in Birmingham, England used a cyclotron-produced pulsed neutron beam, but other groups in the United Kingdom, United States, Canada, and New Zealand subsequently developed systems based on radioisotope neutron sources that could measure body nitrogen with a precision of a margin of error of a few percentage points. The accuracy of N measurement was greatly enhanced by Vartsky's internal standardization, using prompt-gamma H as the marker and total body hydrogen (based on total body water and skinfolds) as the reference. Chlorine and extracellular water volume were used in a similar way by the Swansea group to calibrate the prompt-gamma analysis of total body calcium. The PGIVNA technique is most valuable in assessing nutritional status, particularly in relation to body protein.