Table 3.
Parameters’ definition and connotation in image quality
| Evaluation | Parameters | Definition | Connotation in image quality |
| CL | Overall quality | Image quality in general, not considering a specific parameter | Higher = better |
| Sharpness | Ability to discriminate small structures in an image | Higher = better | |
| Contrast | Ability to distinguish different densities in an image | Higher = better | |
| Artefact | Any distortion or error (like dark bands or dark streaks) unrelated to the real object | Higher = worse | |
| Noise | Graininess in appearance of a supposedly homogeneous structure | Higher = worse | |
| QUANT | MGV shift | Mean of dark artefacts mainly from beam hardening but also from other phenomena | Higher = worse |
| % of increase SD | Percentage of mixed artefacts (light and dark) normalized to the SD of a non-artefact region | Higher = worse | |
| % of beam hardening | Percentage of gray value shift between artefact and control region, divided by the difference between control region and air | Higher = worse | |
| CNR | Difference in gray value between average of soft-tissues and air, divided by root sum of squares of the SDs | Higher = better | |
| TECH | Segm accur air | Segmentation accuracy error of an air-filled region | Higher = worse |
| Segm accur Al | Segmentation accuracy error of an aluminium-filled region | Higher = worse | |
| CNR air | Contrast-to-noise ratio of air vs PMMA | Higher = better | |
| CNR Al | Contrast-to-noise ratio of aluminium vs PMMA | Higher = better | |
| CNR hydrox | Contrast-to-noise ratio of hydroxyapatite vs PMMA | Higher = better | |
| Norm metal SD | Normalized standard deviation of a homogeneous region containing metal artefacts | Higher = worse | |
| Metal object area | Average of the segmented cross-sectional areas of three small titanium cylinders | Higher = worse | |
| FWHM | Sharpness of an edge between air and PMMA | Higher = worse |
Al, aluminium; CL, clinical; CNR, contrast-to-noise ratio; FWHM, full width at half maximum; MGV, mean gray value; Norm metal, normalized metal; PMMA, polymethyl methacrylate; QUANT, quantitative; SD, standard deviation; Segm accur, segmentation accuracy; TECH, technical.