Study on the Medical Universal Human Counter (First Report) Development of MUHC and Fundamental Study on the Whole Body Counting with MUHC
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概要
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<I>A human counter has been designed and constructed which has wide applicability in clinic. This does not have a steel shielded room but four detectors using</I> 3×2 in NaI (Tl) <I>crystals instead of single large crystal. In addition to whole body counting it can be used for almost all kinds of external countings such as temporal scanning, linear scanning and area scanning and it is therefore called "Medical Universal Human Counter (MUHC for short) "</I>.<BR><I>In whole body counting, two detectors are placed over the lying patient and the other two beneath the bed. After the first counting for a certain fixed time the detectors are transferred to another place for the second counting. These two countings give the geometrical arrangement equivalent to the whole-body counting with</I> 8<I> detectors arrayed symmetrically in line above and below body axis provided that counting time is short enough for neglecting the changes of radioisotope distribution. Distance between the detectors adjoining each other is</I> 50cm <I>and that between the detectors opposing is</I> 100cm. <I>The spatial distribution of measurement efficiency is fairly uniform</I> (100±5%) <I>in the limits of</I> 10cm <I>above and below from the mid-point between two opposing detectors and</I> 150cm <I>along the longitudinal axis, in the insertion of a subject, however, intensity of</I> γ-<I>rays decreases exponentially with depth provided that pure photo-peak from a nuclide in the subject is counted. Since the measurement efficiency should be uniform in the opposed combination of two isoresponce curves which decrease linearly with depth, the width of spectrum was studied by which the counting rate of</I> γ-<I>rays decreases linearly with depth. As a result, reduction in water was proved to be linear in the width of</I> 240-400 keV <I>for</I> <SUP>131</SUP>I, 525-725 keV <I>for</I> <SUP>137</SUP>Cs <I>and</I> 1.05-1.45 MeV <I>for</I> <SUP>60</SUP>Co. <I>Generally for the lower energy</I> γ-<I>rays, uniform distribution</I> (100±10%) <I>of measurement efficiency was obtained in the water phantom of</I> 20cm <I>thick by a differential counting including Compton scattered region in addition to photopeak</I>.<BR><I>According to the above-mentioned results, in the practice of whole-body counting with MUHC, the optimal spatial arrangement of the detectors and the optimal channel width of spectrometer should be taken into account. If so, the amount of radioisotope can be measured precisely not influenced by a state of internal distribution of radioisotope.</I> 0.1μCi <I>of</I> <SUP>131</SUP>I <I>in vivo can be measured with relative errors</I> 5% <I>by whole body counting for an hour</I>.
- 社団法人 日本アイソトープ協会の論文
社団法人 日本アイソトープ協会 | 論文
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