Table 2.

Image quality tests and calculation methods

Image quality tests	Definition
Modulation Transfer Function (MTF)a	The modulation of multiple ROIs in the phantom with various line bar patterns. As spatial frequency increases, ROI's modulation decreases. The modulation is normalized to its highest value and plotted.
Modulationa	$\frac{H{U}_{90}-H{U}_{10}}{H{U}_{90}+H{U}_{10}}$ Where $H{U}_{90}$s the 90th percentile CT number in the ROI and $H{U}_{10}M\left(\%\right)$ s the 10th percentile CT number in the ROI.
Scaling Discrepancya	The maximum possible error in a measurement of distance. $\left|M(\%)-100\%\right|\times L$ Where $M(\%)$ is the magnification of the image and $L$ is the length of the image's longest side.
Geometric Distortiona	Verifies that correct distance measurement occurs in all regions of the CT image.
Overall Uniformitya	$\left(1-\frac{Ma{x}_{90}-Mi{n}_{10}}{Ma{x}_{90}+Mi{n}_{10}}\right)\times 100\%$ Where $Ma{x}_{90}$ is the maximum 90th percentile CT number in all uniformity regions and $Mi{n}_{10}$ is the minimum 10th percentile CT number in all uniformity regions
Minimum Uniformitya	The lowest uniformity of all ROIs. Uniformity is calculated as: $\left(1-\frac{H{U}_{90}-H{U}_{10}}{H{U}_{90}+H{U}_{10}}\right)\times 100\%$ Where $H{U}_{90}$ is the 90th percentile of the pixel CT number in the ROI and $H{U}_{10}$ is the 10th percentile of the CT number in the ROI.
Maximum HU Deviationa	The maximum deviation between mean HU value of an ROI subtracted from its defined reference HU absolute value of all calculated HU deviation on an image.
Contrasta	$\left(\frac{H{U}_2-H{U}_1}{H{U}_2+H{U}_1}\right)\times 100\%$ Where $H{U}_2$ is the mean CT number in the region with greater signal and $H{U}_1$ is the mean CT number in the region with lesser signal.
High Contrast‐to‐Noise Ratioa	$\frac{HighContrast}{Noise}=\left(\frac{H{U}_2-H{U}_1}{H{U}_2+H{U}_1}\times 100\%\right)/\left(\frac{\sqrt{({\mathit{\sigma }}^2)+{({\mathit{\sigma }}_1)}^2}}{\sqrt{{(H{U}_2)}^2+{(H{U}_1)}^2}}\right)\times 100\%$ Where ${\mathit{\sigma }}_1$ is the standard deviation of the high contrast ROI, ${\mathit{\sigma }}_2$is the standard deviation of background, $H{U}_1$ is the mean CT number of the high contrast ROI and $H{U}_2$ is the mean CT number of background.
Low Contrast‐to‐Noise Ratio13	$\frac{LowContrast}{Noise}=\frac{\left|H{U}_{ROI}-H{U}_b\right|}{{\mathit{\sigma }}_b}$ Where ${\mathit{\sigma }}_b$ is the standard deviation of the background ROI, $H{U}_{ROI}$ is the mean CT number inside the low contrast ROI and $H{U}_b$ is the mean CT number of the background ROI.

^aDefinitions derived from DoseLab v.6.6 User Manual.17