Depiction of Low-Contrast Detail in Digital Radiography: Comparison of Powder- and Needle-Structured Storage Phosphor Systems

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Purpose:We sought to evaluate the low-contrast performance of a newly developed needle image plate/line scanner (NIP) computed radiography system in comparison with a standard powder image plate/flying-spot scanner (PIP) system.Materials and Methods:A total of 36 images of a CDRAD phantom, simulating low-contrast structures with different drill holes of different diameters, were obtained with both imaging systems using 9 different exposure variables. All images had window and level set to generate consistent density and contrast. In addition, multiscale contrast-dependent contrast amplification was applied to some of the images. All images obtained were printed and presented to a total of 10 observers (5 radiologists, 5 engineers/physicists), who were blinded to both the image plate and parameter setting used. The smallest detectable drill hole depth (= contrast) correctly identified was recorded for each diameter. The median values observed were calculated and tested for statistical differences between PIP and NIP using Student t test for matched pairs (level of significance P ≤ 0.05).Results:At all but 2 settings of the variables, NIP images depicted significantly lower contrast levels (= lower depth of drill holes) compared with PIP images. The 2 settings also showed a trend towards better low contrast depiction with NIP. In no case was low contrast performance better using PIP images.Conclusion:Images obtained with needle image plate/line scanner provide superior low contrast performance compared with the images obtained with powder image plate/flying-spot scanner.

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