Trouble with planar imaging - Las Vegas

Google Groups
,
1

Hello together,
I have some problems with the planar imaging module. I’m using a Las Vegas phantom.

When I change the arguments of the analyze-method, the content of the results-method changes, the right side of the plot of the plot_analyzed_image-method changes - but the left side of the plot of the plot_analyzed_image-method does not change.

This happens no matter which image I use. I tried a couple of our own images, even the from_demo_image does not work.
Inverting the image does not help.

For better understanding, here two screenshots.

Thank you a lot for any idea.

1.png
1.png1380×786 123 KB
2.png
2.png1399×854 137 KB

2

Hi,

the color is defined by the visibility: https://pylinac.readthedocs.io/en/latest/topics.html?highlight=visibility#visibility

you can set the threshold with the visibility_threshold at the end of the analyze function

lv.analyze(0.05, 0.5, False, None, None, None, ssd = 1000, low_contrast_method = pylinac.core.roi.Contrast.MICHELSON, visibility_threshold = 50)

regads
Thomas

3

Thanks a lot for that hint, I will try this out tomorrow.

4

Hey,
it still does’nt work as expected…
How does pylinac count the ROI? Left to right? Top to bottom?
I can’t see any relation between the graph on the right side of the plot, the image on the left side of the plot and my actual dicom-image. Which ROI is, let’s say ROI No 2 in the plot, in my actual image?
I understand that the number of ROIs detected match the number of ROIs above the violet line, but which ROI in the image do they represent?

When I change the visibility_threshold, then the number of green (visable?) ROIs in the left part of the plot changes. But still, there are ROI green which I can barely see and other ROIs are still red - but they are very good visible in the image.

Or do I misunderstand the meaning of the red, green and blue circles in the left part of the plot?

Thank you a lot!

5

Hi,

the ROI numbers can be found in the soruce code here:
https://pylinac.readthedocs.io/en/latest/_modules/pylinac/planar_imaging.html#LasVegas
it seems to be defined by a polar coordinate system.

Why the sqrt(DQE) equals 1/I_stddev I don’t know. Maybe James can give us a hint. I did not find the conversion in the mentioned papers.