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dkazanc / TomoPhantom

Software to generate 2D/3D/4D analytical phantoms and their Radon transforms (parallel beam) for image processing
https://dkazanc.github.io/TomoPhantom/
Apache License 2.0
116 stars 53 forks source link

Negative amplitude? #82

Closed jakeoung closed 4 years ago

jakeoung commented 4 years ago

Thanks for this amazing work! I have a question of how to set the linear attenuation numbers.

I guess the amplitude in the paper indicates the attenuation values, right? If then, I see some negative values in some data (e.g., in 3d Shepp-Logan -0.8 below) Can I know if it's fine to set negative values?

#----------------------------------------------------
#  3D Shepp-Logan
Model : 13;
Components : 10;
TimeSteps : 1;
Object : ellipsoid 1.0 0.0 0.0 0.0 0.69 0.92 0.81 0.0 0.0 0.0
Object : ellipsoid -0.8 0.0184 0.0 0.0 0.6624 0.874 0.78 0.0 0.0 0.0
dkazanc commented 4 years ago

Hi, thanks for using Tomophantom. These values are related to the density of objects. So they can be negative when you'd like to 'carve out' one object from another, 1.0-0.8=0.2 will be the resulting density. After taking Radon transform from the objects you'll get their attenuation coefficients. Hope it helps.

jakeoung commented 4 years ago

Yes, thanks a lot! It helps me understand better!