Extended-cycle processによる乳房撮影用増感紙／フィルムシステムの画質改善

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  • Improvement of image quality on mammographic screen-film system by extended-cycle process

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Extended-cycle process is the term used for a processor in which the processing time has been prolonged usually to approximate 210 seconds. It has been known that the extended-cycle process of some single-emulsion films as used for mammography may enhance film contrast and increase film speed. So the speed was increased in lower speed and higher resolution system than conventional systems by means of using the extended-cycle process in this paper. We investigated how much the resolution of the system was kept. A single screen-single emulsion combination, Konica M-100/CM-H was employed as a low speed and high resolution system. This film after exposure was processed in the different combinations of developing temperatures, 30, 32 and 34℃, and processing time of 210 seconds. On the other hand, Konica M-200/CM-H was employed as a high speed system. This film was processed in the standard-cycle processing (34℃, 90 seconds). Those systems were compared on contrast, speed, screen-film blur and noise by a characteristic curve, MTF (modulation transfer function) and WS (wiener spectrum). Furthermore, the RMI 165 phantom was used to evaluate visibility of mammographic details of these systems. As a result, in the extended-cycle process at the developing temperatures of 32 or 34°C and processing time of 210 seconds for M-100/CM-H, it was possible to increase the speed as much as the higher speed system, M-200/CM-H. Then the contrast, the MTF and the visibility were also improved as compared to the higher speed system. Furthermore patient dose could be reduced at the developing temperature of 34℃ and processing time of 210 seconds in M-100/CM-H.

通常,extended-cycle processは処理時間が約210秒に延ばされた現像機のために使われる用語である｡乳房撮影に使われるような片面乳剤フィルムにおけるextended-cycle processは,フィルムコントラストを増し,感度をあげることが良く知られている｡そこで,本論文ではextended-cycle processにより低感度,高解像度システムの感度を上げ,どの程度解像度が維持されるかを調べた｡片面増感紙／片面フィルムの組合わせであるKonica M-100/CM-Hを低感度,高解像度システムとして用いた｡露光後のフィルムは現像温度30,32, 34度,処理時間210秒の異なる組合わせで現像処理した。一方,高感度システムとしてKonica M-200/CM-Hを用い,このフィルムは標準現像(34℃,90秒)された｡感度,増感紙／フイルムのぼけ,雑音に関して,特性曲線,MTF(modulation transfer function), WS(wiener spectrum)によってこれらのシステムを比較した｡さらにこれらのシステムにおける乳房写真の細部視覚評価のためにRM165ファントムを使用した｡その結果,M-100/CM-Hに対するextended-cycle process現像温度32, 34℃,処理時間210秒のextended-cycle processにおいて,高感度システムM-200/CM-Hと同等の感度を上げることが可能であった｡そのとき,コントラスト,MTF,視覚的検出能も高感度システムより向上した｡さらに,現像温度34℃,処理時間210秒では,被曝線量の低減が可能であった｡

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