In order to determine the tritium concentration in environmental water samples, the electrolytic enrichment was carried out with (St) and without (S) addition of tritiated water of a certain concentration (deuterium-free) to the samples. With the use of the fundamental formulas on electrolytic enrichment, the deuterium concentration (Dit)before electrolysis for an environmental water sample is determined by liquid scintillation counting and densitometry for the sample St. Furthermore, the tritium concentration in the environmental water sample is determined by the above methods for the sample S, and by the substitution of Dit for Di in the formulas. Tritium concentrations in environmental water samples were found to be determined within an accuracy of 10% by this method when Vi/Vf was 14-25. It is considered that this method dispenses with the direct measurement of low deuterium concentrations (Di) before electrolysis, a special technique on the purification of water for densitometry, and moreover, excludes the possibility of cross contamination in the electrolytic enrichment by the spike cell method.
It has been investigated whether isotope-exchange reaction occurs or not between unlabeled poly (vinyl alcohol) (PVA) and water vapor (containing HTO molecules) (gas-solid reaction at 50°C and 70°C) . For each PVA sample the activity was measured after the reaction for an arbitrarily chosen time. The relation between the specific activity (of each sample) and the reaction time was examined. Two kinds of PVA were used. One (PVA500) has the degree of polymerization of 500, and another (PVA2000) has that of 2000. Then another exchange reaction (liquid-solid reaction) has been investigated where the reactants are isoamyl alcohol and labeled PVA (PVA500or PVA2000) . For each isoamyl alcohol sample the activity was measured after the reaction for a prescribed time. The time dependence of the specific activity of each sample was examined. In the analysis of reactions, McKay plots and A''-McKay plots were used (the latter plots are based on a novel equation) . Two kinds of reactions have been found for both PVA500and PVA2000in both gas-solid reaction and liquid-solid reaction. The initial part of reaction always corresponds to the exchange reaction at the surface of PVA samples, and the latter part to that at the inner part. The degree of reactiveness of H atoms in the surface layer of PVA500samples is higher than that in the surface layer of PVA2000samples in both the reactions.
ECG-gated thallium (201Tl) myocardial diastolic imaging and non-gated imaging were performed in 22 patients with myocardial infarction. These patients were separated into 2 groups according to echocardiographic findings; Group A: the patients with left ventricular diastolic diameter of 5.5 cm and over and left ventricular ejection fraction of 50% and under; Group B: the others. In the patients of Group A, the low perfusion areas could be demonstrated qualitatively and quantitatively by nongated images as well as gated-diastolic images, while in some patients of Group B, low perfusion areas were shown only by gated-diastolic images, which seemed to be useful. The images gated in 100 ms after the peak of R wave in ECG were conformed as diastolic images by echocardiography, and could be obtained within a half or two thirds of the conventional imaging time.
Using cadmium telluride (CdTe) as a detector, we assembled a computerized single probe system. The size of the CdTe used is 16 mm in diameter and 2 mm in thickness. Two types of the straight bore collimators of 16 mm in diameter were prepared. One is 16 mm in length (long type) and the other is 5 mm in length (short type) . The response curves of the long and short type collimators to57Co in water showed that the points at 10% of maximum counts were 4 cm and 3 cm in depth along the center axis. The data were accumulated by using a commercialized single cardiac probe system (OMNISCOFE) and processed by itself or transferred to the microcomputer (LSI-11/23) for further analysis. Twenty percent count loss occurred at 100000 cps with an integral discriminator setting. This system was applied for cerebrospinal fluid (CSF) shunt flow evaluation and measurement of left ventricular ejection fraction (LVEF) . Measurement of CSF shunt flow has been able to do in any patient's positioning. In 21 patients with various heart diseases, LVEFs obtained by CdTe detector were compared with those obtained by scintillation detector. There was good correlation between the LVEFs obtained by these two detectors: correlation coefficient (γ) =0.939.