Slice thickness CatPhan504

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1

See if anybody can help me…
Using CatPhan504, for some CT scans slice thickness measured is 10 times less than expected using both raw and reconstructed CT. Manual analisys of FWHM gives bak the expected values. Everything else in the analisys is perfect… any ideas?

my_TC= CatPhan504(directori)

hu_tolerance_=40
50mm_tolerance=0.5
thickness_tolerance_=0.2
low_contrast_tolerance_=1
cnr_threshold_=6
my_TC.analyze( hu_tolerance=hu_tolerance_, scaling_tolerance=50mm_tolerance, thickness_tolerance=thickness_tolerance_,
low_contrast_tolerance=low_contrast_tolerance_, cnr_threshold=cnr_threshold_)

…

print(my_TC.results()) gives me:

Geometric Line Average (mm): 50.01
Geometry Passed?: True

Measured Slice Thickness (mm): 0.179

Slice Thickness Passed? False

Nominal slice thickness is 2.5.

Any ideas?
Manual analisys of FWHM gives back values around 2.5mm

2

Hi,

How much are you getting for slice thickness?

Did you check if Pylinac is showing the CTP404 slice correctly? That is, if the wires are seen.
How much noise do you have in the images?

Denis

3

Hi Denis.
The image is really “far” from view… could it be the problem? I can’t even see the image myself…

4

Can you show us an image of the slice?

If the image is very noisy, then it is highly likely that Pylinac will not find the wires. And because you have very small measured slice thickness, I think that may be the cause. Pylinac may have found an artifact that looks like a wire.

Denis