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

<i>Aim</i>. 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.<i>Material and methods</i>. Pixel sizes ranged from 175 (detector A₁₇₅) to 76<i>μ</i>m (detector G₇₆). Modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using International Electrotechnical Commission (IEC) RQA3 beam quality. Threshold contrast (<i>C</i>_T) and a detectability index (<i>d</i>') 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 E₁₂₄.<i>Results</i>. The 10% point of the MTF ranged from 3.21 to 4.80 mm^-1, in going from detector A₁₇₅to detector G₇₆. DQE(0.5 mm^-1) measured at 2.38<i>μ</i>Gy/image was 0.50 ± 0.05 for six detectors, but was higher for F₁₀₀at 0.62. High frequency DQE was superior for the smaller pixel detectors, however<i>C</i>_Tfor 0.25 mm discs correlated best with DQE(0.5 mm^-1). Correlation between<i>C</i>_Tand the detectability model was good (<i>R</i>²= 0.964).<i>C</i>_Tfor 0.25 mm diameter discs was significantly higher for D₁₅₀and F₁₀₀compared to E₁₂₄. The visual grading data revealed higher image quality ratings for detectors D₁₂₅and F₁₀₀compared to E₁₂₄. An increase in air kerma was associated with improved perceived sharpness and overall quality score, independent of detector. Detectors B₁₅₀, D₁₂₅, F₁₀₀and G₇₆, performed well in specific tests, however only F₁₀₀consistently outperformed the reference detector.<i>Conclusion</i>. Pixel size alone was not a reliable predictor of small detail detectability or even perceived sharpness in a visual grading analysis study.