The physical characteristics of a clinical amorphous silicon-based flat-panel imager for full-field digital mammography were investigated. Pre-sampled modulation transfer functions (MTF) were measured by using a slit method. Noise power spectra were determined for different input exposures by fast Fourier transform. The MTFs of full-field digital mammography systems showed significantly higher values than those of the computed radiography (CR) system. The full-field digital mammography system showed a lower noise level than that of the CR system under the same exposure conditions. Contrast detail analysis has been performed to compare the detectability of the full-field digital mammography system with that of the screen-film (Min-R 2000/Min-R 2000) system. The average contrast-detail curves of digital and film images were obtained from the results of observation. Image quality figures (IQF) were also calculated from the individual observer performance tests. The results indicated that the digital contrast-detail curves and IQF, on average, are superior to those of the screen-film system.

We investigated the clinical usefulness of a newly developed flat-panel detector (FPD) system by comparing its physical imaging properties and low-contrast detectability with those of a current FPD system. The newly developed CsI-based indirect FPD (Canon, CXDI-40C) and current Gd(2)O(2)S-based FPD (Canon CXDI-11) systems were used. Characteristic curves, resolution properties, radiographic noise, detective quantum efficiencies (DQEs) and low-contrast detectability for both systems were measured. The new FPD system showed considerably lower noise levels than those of the current FPD system. DQE (0) s of the new and current FPD systems were 75% and 35%, respectively. Observer performance tests of the contrast-detail (C-D) phantom indicated that the new FPD system can significantly improve low-contrast performance over that obtainable with the current FPD system under the same conditions of exposure. The new FPD system provided approximately 50% reduction in exposure while providing comparable detectability. The newly developed FPD system provides radiographic images with excellent inherent physical image quality and low-contrast performance.

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【目的】 CsI フラットパネルを用いた胸部撮影において四つの X 線線質(90 kV 0.15 mmCu-filter, 90 kV 0.2 mmCufilter, 120 kV filter なし，および 120 kV 0.2 mmCu-filter)のコントラストノイズ比(CNR)をモンテカルロシミュ レーションによって検討した． 【方法】 20 億個の光子を模擬結節(直径 10 mm, CT 値：+30 Hounsfield unit (HU) ， −375 HU, −620 HU)をもつ胸部ファントムモデル(幅：300 mm, 長さ：300 mm, 厚さ：200 mm)に入射させた． 個々の一次と二次光子のファントムと CsI 内での推移(吸収，散乱，および透過)をモンテカルロシミュレー ションによって追跡した．そのうちの CsI で吸収される一次光子数と二次光子数から模擬結節の CNR を計算し た． 【結果】 90 kV 0.15 mmCu と 90 kV 0.2 mmCu 線質は高い一次線被写体コントラストと一次光子寄与率，また CsI に対する高い光子吸収率のため 120 kV 線質より高 CNR となる． 【結語】モンテカルロシミュレーションに よって 90 kV 0.15 mmCu, 90 kV 0.2 mmCu 線質は 120 kV 線質に比べて高 CNR となることを実証した．