Post-processing in digital radiography. A burden or a blessing?

International Conference on Medical Physics

August 03-05, 2015 Birmingham, UK

Robin Decoster, HarrieMol and Dirk Smits

Posters-Accepted Abstracts: J Nucl Med Radiat Ther

Abstract :

The dynamic range of modern detectors tolerates a higher detector dose or Detector Air Kerma (DAK) without deteriorating the image quality. The purpose was to investigate the relation between image quality, as overall judgment versus the visibility of well-defined structures, and DAK in clinical radiographs. Furthermore the Contrast-Noise Ratio (CNR) was examined as a measure of image quality. 168 knee and 152 pelvis radiographs were collected randomly in 19 radiologic centers. Six experienced radiologists scored the overall image quality and the visibility of seven different anatomic structures with a Visual Grading Analysis (VGA). The relation between DAK and VGAScore (VGAS) was evaluated. To investigate the role of post-processing, a TOR18FG phantom with 5cm PMMA was exposed to different dose levels. On a low and high contrast element, with and without post-processing, the CNR was calculated. The VGAS was 3.92 for the knee and 3.71 for the pelvis. Intra-observer variability wasnâ??t significant and inter-observer correlations were high and significant. For the pelvis radiographs on computed radiography, a weak but significant correlation was found between DAK and VGAS. The post-processing weakens the DAKCNR relationship above 4mGy in high contrast elements and nullifies it for low contrast elements. The VGA revealed an image quality higher than diagnostically necessary in both datasets. A hypothesis is that DAK influences the CNR up to a certain point, after which the post-processing is the dominant parameter. CNR saturation, a stagnation of CNR in function of DAK may explain the absence of a relation between DAK and VGAS.