α-Rays from atmospheric radionuclides, i.e. radon and its daughters (222Rn, 218Po and214Po) fluctuate background counts of liquid scintillation counters, since they are sensitive to the luminescence of nitrogen molecules excited by the α-rays. The background count was decreased and its fluctuation was suppressed by passing nitrogen gas through its detector chamber; for example the count rate of tritium free water sample, which fluctuates in the range of 3-5 min-1without the gas flow, was decreased to 3.2±0.3 min-1.
We made a solid scintillator holder which can be used in place of liquid scintillation cocktails to measure the radioactivity of32P with a liquid scintillation counter (Beckman LS-1801), and got a satisfactory result on counting efficiencies for the nuclide. Our method has the following advantages: (1) Fairly high counting efficiencies may be expected. (2) No sample preparation is required for colored solutions. (3) The sample is unaltered by counting and can be used further for other purposes. (4) The holder is cheap to make.
In order to investigate the clinical usefulness of positron emission tomography (PET) studies using the inhalation of oxygen-15 labeled gas, clinical trial was performed. PET studies were carried out using15O labeled gas produced by automated15O gas production system (ARIS G1) in 72 patients with various neurological disorders. In all cases, the labeled gas was produced in a stable condition by ARIS G1 and no adverse reaction was observed. Overall assessment for the clinical usefulness of PET study using ARIS G1 was determined as follows: 50% as highly useful, 41.7% as useful and 8.3% as fairly useful. In conclusion, PET studies using15O gas production system were useful in patients with various brain diseases.