In radioactivity monitoring, analytical radioassay for nuclides in a monitoring sample is the first choice to be carried out for reasonable countermeasure. The method of least squares has been applied to the radioassay for relatively low-level pure β-emitter mixtures (3H, 14C, 32P and45Ca) in radioactive waste solution and organic liquid waste. This liquid scintillation technique can get rid of the difficulty of the analysis for a pure β-emitter mixture in a monitoring sample, and provides fundamental information for subsequent waste-treatment. Detection limit of the four nuclides was estimated to be 0.2 -1.0 Bq/cm3, which is sufficiently low compared with the values for authorized safety guideline.
In order to examine the clinical value of positron emission tomography (PET), we measured cerebral perfusion and oxygen metabolism using oxygen-15 labeled gas (O2, CO2, CO) produced by small cyclotron and the automated synthesis system (AMGS 01) . PET study was carried out using oxygen-15 continuous inhalation technique in 61 cases with various neurological diseases including cerebrovasculardisease (39 cases), dementia (6 cases), brain tumor (3 cases) and other neurological diseases (13 cases) . In all cases, the labeled gas was produced and delivered in a stable condition. Functional images of regional cerebral blood flow (CBF), oxygen extraction fraction (OEF), cerebral metabolic rate for oxygen (CMRO2), and cerebral blood volume (GB V) were calculated according to the oxygen-15 steady-state model. Visual interpretation of these functional images showed abnormal findings in 74% (CBF images), 30% (OEF images), 79% (CMROO2image) and 10% (CBV image) of the total cases. Overall assessment for the clinical usefulness of this method was determined as follows; 28% as highly useful, 41% as useful, 31% as fairly useful. No adverse reaction was observed in this clinical trial. In conclusion, the automated synthesis system provided a stable delivery of oxygen-15 gas, and PET measurement of cerebral blood flow and oxygen metablism is a valuable technique not only for clinical diagnosis but also for understanding pathophysiology of various neurological diseases.
The in vivo localization of a polyclonal antibody (GP68 PoAb) against a glycoprotein, which was found in developing mouse brain, was studied in murine tumor model. The biodistribution of125I-GP68 PoAb 3 days postinjection into the mice bearing eight different kinds of solid tumor represented a high uptake ratio by metastatic lung cancer, mammary tumor such as MMT 060562 and adenocarcinoma 755, and melanoma B-16. In immunoscintigraphic studies, adenocarcinoma 755 and metastatic lung cancer were successfully visualized with131I-GP68 PoAb at 3 days postinjection. The strongly positive images of these tumors with131I-GP68 PoAb were accorded well with the data on tissue distribution of this antibody. These results suggest that GP 68 PoAb may be applicable to the detection of the mammary and/or metastatic lung cancer.
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.