| 摘要 |
PURPOSE:To detect gamma-ray with noise reduced by grouping gamma-ray detectors unequally, combining groups of detectors to make the shape of effective visual field to necessary ranges and making its fan fraction small. CONSTITUTION:Detectors (black circles) arranged on the circumference of a gamma-ray detecting device are grouped unequally, for instance, 13 in the first group, 15 in the second group, 15 in the third group 3-13 in the ninth group. Opposite groups, for instance, the 4-7th groups are selected for the first group, and the shape of pseudo ellipse of effective visual field 31 of good resolution is obtained. The fan fraction, a ratio of a simultaneous count detector and a total detector is made small by combining the detector groups properly. Accordingly, even if the fan fraction is small and the effective visual field is pseudo ellipse, detection can be made conformable to the shape of a subject and little noise as cephalic section the thoracic section are elliptic. |
