In our previous version of pylinac (2.x), the planar_imaging “StandardImagingQC3” class included the low_contrast_background_roi in the list of all the low contrast roi’s to be analyzed:
low_contrast_roi_settings = {
‘roi 1’: {‘distance from center’: 2, ‘angle’: 90, ‘roi radius’: 0.5},
‘roi 2’: {‘distance from center’: 2, ‘angle’: -90, ‘roi radius’: 0.5},
‘roi 3’: {‘distance from center’: 2.4, ‘angle’: 55, ‘roi radius’: 0.5},
‘roi 4’: {‘distance from center’: 2.4, ‘angle’: -55, ‘roi radius’: 0.5},
‘roi 5’: {‘distance from center’: 2.4, ‘angle’: 128, ‘roi radius’: 0.5},
‘roi 6’: {‘distance from center’: 2.4, ‘angle’: -128, ‘roi radius’: 0.5},
}
low_contrast_background_roi_settings = {
‘roi 1’: {‘distance from center’: 2, ‘angle’: 90, ‘roi radius’: 0.5},
}
Analyzing contrast of the background roi will always yield a value of 0 and skew median contrast values downward.
In our new version of pylinac the QC3 class now excludes the background roi from the list of low contrast rois to be analyzed. This is consistent with all other phantoms except the new planar_imaging kV “StandardImagingQCkV” class.
Is it possible that the new QCkV phantom was built from the original MV QC3 phantom, but did not include this update to omit the background low contrast roi from analysis?