A device for dispensing radioactive xenon gas.

Abstract

A number of technics have been described for extracting radioactive xenon gas from glass shipping vials and quantitatively dispensing and dissolving it in physiological saline (1, 2). In large institutions, where 133Xe is widely used as an indicator of blood flow and regional ventilation, the quantity of gas which can be obtained in a single glass shipping vial is usually insufficient. Curie quantities of 133Xe can be obtained from the Oak Ridge National Laboratories, Tenn., in cylinders which have internal volumes from 10 to 50 cc at a gas pressure of approximately 10 mm Hg. This communication describes a device which has been designed and constructed to readily dispense 133Xe from these gas cylinders. High purity CO2 is used to fill the 133Xe cylinder to a pressure of three atmospheres. This enables a small quantity of the 133Xe-CO2 gas mixture to be readily withdrawn from the cylinder through a micrometer needle valve. Carbon dioxide is used as the pressurizing gas since a Xe-CO2 mixture can be more readily dissolved in saline for intravenous injection than can a Xe-air mixture. A circuit diagram of the device is illustrated in Figure 1, and the actual unit is shown in Figure 2. A full cylinder of 133Xe is rigidly held in a large metal ring by means of three positioning screws. Before this cylinder is attached to the dispensing unit, air is flushed out of the unit with CO2 The xenon cylinder is then attached to the dispensing device by means of the Swagelok connector, and the system is sealed. Opening of the tank shut-off valve and the filling valve allows gas from the CO2 cylinder to fill the 133Xe cylinder to a pressure of three atmospheres. After closure of the filling valve, the circuit is ready for dispensing radioactive gas. To extract 133Xe from the unit, a syringe and stopcock are attached to the stopcock on the unit, and a bubble of radioactive gas is slowly expelled into the syringe by opening the micrometer needle valve. The amount of 133Xe dispensed can be measured by placing the syringe inside a calibrated well-type ionization chamber. Radioactive xenon gas which is to be used in a closed-circuit spirometer system can be taken up into a Hamilton gas-tight syringe for transfer. For intravenous injection, a bubble of the 133Xe-CO2 mixture can be taken up into a 20-cc syringe containing a volume of sterile saline, in which most of the gas will readily dissolve. Aliquots of xenon-saline for injection can be taken out of the syringe through the three-way stopcock. The physical layout of the dispensing unit is shown in Figure 2. The xenon gas cylinder and the dispensing syringe are mounted behind a lead and stainless-steel barrier.