[Rtk-users] Reconstruction Artifact

[Benjamin W. Maloney]

Hi,

I thought the same in regards to trying to rotating in the other direction. Unfortunately, that has a similar artifact but with the reconstruction flipped.
Interestingly the overlap happens in a similar place but the internal structures are flipped

​1. Thanks!
2. I should have worded that better. My projection images will be preprocessed in a float format. I wanted to check if there were restrictions on these float values. Can input image data have negative values or high values? Or are they expected to have values between 0 and 1? I ask because some of the tools I have used to do this preprocessing (outside of RTK) have given negative values or 'stretched' the data from 0 to 255 before saving.

Ben

________________________________
From: Simon Rit <simon.rit at creatis.insa-lyon.fr>
Sent: Tuesday, June 2, 2020 5:28 PM
To: Benjamin W. Maloney <Benjamin.W.Maloney.TH at dartmouth.edu>
Cc: rtk-users at public.kitware.com <rtk-users at public.kitware.com>
Subject: Re: [Rtk-users] Reconstruction Artifact

Hi,
Sometimes rotating in the wrong direction gives this kind of artefacts. It's quite possible that we don't use the same convention as other toolkits regarding this.
For other questions:
1. Yes, you can use pixel as the unit. Then the image spacing should be 1 obviously and indeed, sdd and sid should be in pixels.
2. I don't fully understand. If your data is the output of a count detector, then you either rely on RTK to guess the counts without object to compute the line integral, or your preprocess your projections to pass line integrals in a float format.
Simon

On Tue, Jun 2, 2020 at 4:51 PM Benjamin W. Maloney <Benjamin.W.Maloney.TH at dartmouth.edu<mailto:Benjamin.W.Maloney.TH at dartmouth.edu>> wrote:
Hi all,

Not sure if this is the right group to post to but here's my question:

I have a code that pulls in my own projection images and uses the FDKConeBeamReconstructionFilter for reconstruction

The reconstruction I am getting has an artifact where it looks like there are two overlapping objects rotated.
I have used other reconstruction toolboxes (mainly TIGRE in MATLAB) with the similar geometry inputs and not had this issue. I suspect the difference is in the parts of the geometry that are set by default. My question is if anyone has seen this before and what input I should look into?

I have a few more questions I may or may not be related:
1. I assume that since I set the origin etc of my images in pixel, sid and sdd should be in pixels as well?
2. Are there restrictions related the scalar values of the projection data? My data will be in detector counts rather than linear attenuation coefficients, is that okay?
I have attached an image to show this issue. It is supposed to be a rectangular mammography phantom. It is a slice in XZ plane

Thanks for the help!
Ben



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