Plastic scintillation filament detector system for 14CO2 breath-analysis tests.

A 14CO2-measuring system for breath-analysis tests is described which utilizes plastic-scintillator filaments as radiation-detector elements. The 14C radioactivity in expired breath is measured directly, thus eliminating the need for trapping and counting of liquid scintillation-counting solutions. Total CO2 concentration in expired breath is measured by an infrared detector, making no assumption of endogenous CO2 output and enabling results to be expressed as either a concentration (percentage of administered dose per unit of CO2) or total expired 14CO2. Advantages of this system over an ionization chamber are: significantly lower background variation and shorter breathing time to fill completely the detecting chamber with expired air. The system is easy to operate, transportable on a small cart to the patient's bed if necessary, and applicable for continuous monitoring of 14CO2 in experimental animal studies.