Scatter images have angle dependence when rotating phantom

Particle, Track & Event
#1

Dear GGEMS-developers,

I found a strange behavior about scattered images when calculating projection images of a water tube phantom for CBCT reconstruction. The intensity of the scattered images slightly differs depending on the projection angle, even if the phantom is rotationally symmetric. Especially, the intensity of the scattered images are slightly higher only when the projection angle is around 0 deg.
I checked primary images by substracting scattered images from total images, the primary images had no angle dependence.

This behavior only occurs when I rotate the water tube phantom. If I fix the water tube phantom and rotate the detector and x-ray source, the scattered image have no angle dependence.

I attached examples of total and scattered images of 0, 90, and 180 degree. The Window/Level are the same for all images. (I simulated half-scan mode, so the projection images are shifted.)

Is it possible to fix this behavior?

Thank you

example
example699×929 135 KB

#2

Dear Tanaka Naka,

Thank you for using GGEMS and send us your problem about your behavior concerning scatter. I will try to fix this problem as soon as possible. I send you another message here when I fix the problem. I will commit the patch in the devs branch for moment, and in a small release later (1.1.1)

Kind regards
Didier

#3

Dear Didier,

Thank you for answering my question. I’m looking forward to using the new version.

Thank you
Tanaka Naka

#4

Dear Tanaka Naka,

I fixed the problem. It was a problem between global and local position during the tracking step. I pushed the patch on the devs master. I will make a release 1.1.1 in the next few days. Tell me if it’s ok with your results.
Thank for finding the bug.
Kind regards
Didier

#5

Dear Didier,

I installed the devs version and the results were fine.
Thank you for promptly solving the problem!

Best regards,
Tanaka Naka