Seven general radiography x-ray detectors with pixel sizes ranging from 175 to 76 μ m: technical evaluation with the focus on orthopaedic imaging

Aim . Flat panel detectors with small pixel sizes general can potentially improve imaging performance in radiography applications requiring fine detail resolution. This study evaluated the imaging performance of seven detectors, covering a wide range of pixel sizes, in the frame of orthopaedic applications. Material and methods . Pixel sizes ranged from 175 (detector A 175 ) to 76 μ m (detector G 76 ). Modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using International Electrotechnical Commission (IEC) RQA3 beam quality. Threshold contrast ( C T ) and a detectability index ( d ′) were measured at three air kerma/image levels. Rabbit shoulder images acquired at 60 kV, over five air kerma levels, were evaluated in a visual grading study for anatomical sharpness, image noise and overall diagnostic image quality by four radiologists. The detectors were compared to detector E 124 . Results . The 10% point of the MTF ranged from 3.21 to 4.80 mm −1 , in going from detector A 175 to detector G 76 . DQE(0.5 mm −1 ) measured at 2.38 μ Gy/image was 0.50 ± 0.05 for six detectors, but was higher for F 100 at 0.62. High frequency DQE was superior for the smaller pixel detectors, however C T for 0.25 mm discs correlated best with DQE(0.5 mm −1 ). Correlation between C T and the detectability model was good ( R 2 = 0.964). C T for 0.25 mm diameter discs was significantly higher for D 150 and F 100 compared to E 124 . The visual grading data revealed higher image quality ratings for detectors D 125 and F 100 compared to E 124 . An increase in air kerma was associated with improved perceived sharpness and overall quality score, independent of detector. Detectors B 150 , D 125 , F 100 and G 76 , performed well in specific tests, however only F 100 consistently outperformed the reference detector. Conclusion . Pixel size alone was not a reliable predictor of small detail detectability or even perceived sharpness in a visual grading analysis study.