I guess the extreme negative values are due to truncation. I have never worked on the interior problem before so I don't have experience with this but I'm not surprised that you reconstruct bad values. The implemented correction is Ohnesorge, B.; Flohr, T.; Schwarz, K.; Heiken, J. & Bae, K. Efficient correction for CT image artifacts caused by objects extending outside the scan field of view *Med Phys, **2000**, 27*, 39-46 The parameter is the ratio of extension (between 0 and 1). Simon
On Wed, May 17, 2017 at 3:41 PM, Jacob Frøsig <[email protected]> wrote: > Hi, > > > > Thank you, it is a great help! Attached is a report describing the project > where the beginning of chapter 5 describes the data acquisition. > The investigated object is an oil pipe. Yes, the reconstruction contains > the expected interior part of the oil pipe along with the ring artefact > > which is characteristic for the interior problem. > What puzzles me is that I get a few extreme negative values, -1.5884e+38 > , in the bottom of the reconstruction using FDKConeBeamReconstructionFilte > r. I have attached the truncated reconstruction without negative values > and the reconstruction with negative values. What exactly is your > truncation correction? > > Have you seen something similar before? > > > > Best regards, > > > > Jacob > > > > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Simon > Rit > *Sent:* 17. maj 2017 15:03 > > *To:* Jacob Frøsig <[email protected]> > *Cc:* [email protected] > *Subject:* Re: [Rtk-users] Reconstructing from fan-beam projections > > > > Hi, > > Here is what I obtain. I have no clue what you expect but that's how I > would translate the geometric information that you provided. The interior > problem is obviously an issue here (our truncation correction does not help > for interior CT) but maybe you can tell us if you recognize your object. > There are clear ring artefacts as well in your sinogram. > > I hope this helps, > > Simon > > > > On Tue, May 16, 2017 at 7:22 PM, Jacob Frøsig <[email protected]> wrote: > > Hi, > > > > yes, it is indeed an interior- / region of interest problem in the sense > that we only are interested in the fully illuminated centre region. > I have previously had success in getting good reconstructions from > interior data using variational formulation with tailored penalty term. > However, this is implemented in Matlab and the aim is to use your > implementation to get a C++ implementation of this method. > > But for now, I am just figuring how to do a simple reconstruction to get a > grasp on the library. > > > > Best regards, > > > > Jacob > > > > > ------------------------------ > > *Fra:* [email protected] <[email protected]> på vegne af Simon Rit < > [email protected]> > *Sendt:* 16. maj 2017 16:59:12 > *Til:* Jacob Frøsig > *Cc:* [email protected] > *Emne:* Re: [Rtk-users] Reconstructing from fan-beam projections > > > > Hi, > > If this is true, then the sinogram indicates that you are dealing with an > interior problem since you have high line integrals at the border (see > enclosed profile). Is that indeed the case? If yes, that's a difficult > problem... > > Simon > > > > On Tue, May 16, 2017 at 3:16 PM, Jacob Frøsig <[email protected]> wrote: > > Hi, > > > > The attached sinogram consist of line integral values, i.e., sinogram(i,j) > = -ln[ *I(i,j)/I_0(i)* ] where *I *and ***I_0 *are the measured > intensities with and without an object, respectively. > Since we are measuring with a line detector, the “zero” (*I_0*) is in > this case just an array. > > *j* is the index for the projections, i.e., *j* ∈ {1,2,…,360} since we > take one projection for each whole angle. > > I hope this explains the sinogram and again; thank you for your time! > > Best regards, > > Jacob > > > > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Simon > Rit > *Sent:* 16. maj 2017 14:54 > *To:* Jacob Frøsig <[email protected]> > *Cc:* [email protected] > > > *Subject:* Re: [Rtk-users] Reconstructing from fan-beam projections > > > > Hi Jacob, > > Thanks for the image of the sinogram. I don't understand this sinogram. Do > you know how to convert each pixel value to a line integral? I.e., if it's > x-ray imaging, do you have an image without object? > > Thanks, > > Simon > > > > On Tue, May 16, 2017 at 2:24 PM, Jacob Frøsig <[email protected]> wrote: > > Hi again, > > and thank you for the example! > > I have some trouble getting a proper reconstruction. If you have the time, > any help would be appreciated. > > Attached is my fan-beam sinogram as a .tif file. Here, projections are > taken for 360 degrees and the detector has 507 pixels. > I believe the issue lies in setting the geometry and maybe the spacing > between the pixels. The measurement geometry is as follows > > Source to centre: 590 mm > > Source to detector: 1000 mm > > Detector length: 411mm > > > > Best regards, > > > > Jacob > > > > > > *From:* Rtk-users [mailto:[email protected]] *On > Behalf Of *Simon Rit > *Sent:* 15. maj 2017 17:32 > *To:* [email protected] > > > *Subject:* Re: [Rtk-users] Reconstructing from fan-beam projections > > > > Hi, > > I have added an example here: > http://wiki.openrtk.org/index.php/FanBeam > > The values in the first and the third rows are not used, as illustrated in > this example. We add them to do a 2D interpolation but we do this 2D > interpolation exactly on the second row so that's not a problem. > > Note that it's a bit more tricky for iterative recon but we also have a > solution for this if you need it. > > Best regards, > > Simon > > > > On Mon, May 15, 2017 at 4:31 PM, Jacob Frøsig <[email protected]> wrote: > > Hi again, > > > > Thank you for the quick answer! An example would be great, thanks. I have > one concern about copying the fan-beam data: > > > Then we would have 2D projections for which each column is the same > fan-beam projection. By this, values of the same row are equal even though > the cone-beam geometry indicates the outer columns correspond to > intensities of rays with longer travel time through the object and hence > should have attenuated more. Is this neglectable? > > > > Again, thanks! > > > > Best regards, > > Jacob > > > > > > > > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Simon > Rit > *Sent:* 15. maj 2017 16:05 > *To:* louie L <[email protected]> > *Cc:* Jacob Frøsig <[email protected]>; [email protected] > *Subject:* Re: [Rtk-users] Reconstructing from fan-beam projections > > > > Hi, > > I agree. What I do is do a 3 slice sinogram from the fan-beam projections > by copying the same data in each slice but reconstruct one 2D slice. If you > need an example, I can quickly demonstrate this in a short Python script. > > Simon > > > > On Mon, May 15, 2017 at 4:01 PM, louie L <[email protected]> wrote: > > Hi, > > > > I think you can carefully pad zeros to your projections. Reconstruct as if > it is a 3d object. Take the middle slice as your fanbeam result. > > Let me know if it helps. > > > > Best regards, > > Louie > > Sent from my iOS > > > Am 15.05.2017 um 15:55 schrieb Jacob Frøsig <[email protected]>: > > Dear Rtk-users > > > > I was wandering if Rtk includes an implementation of a reconstruction > method to reconstruct a 2D representation of an object given fan-beam > projections. > > Or, if anyone has experience using e.g. FDKConeBeamReconstructionFilter > on projections from line-detectors (fan-beam instead of cone-beam). > > > > I hope you guys can help. > > Yours sincerely > > *Jacob Frøsig * > > Project Manager > Sensor Innovation > > FORCE Technology > Park Allé 345 > 2605 Brøndby > Denmark > > Phone: +45 43 25 00 00 <+45%2043%2025%2000%2000> > Direct: +45 43 25 16 43 <+45%2043%2025%2016%2043> > Skype for Business: [email protected] > Fax: +45 43 25 00 10 <+45%2043%2025%2000%2010> > e-mail: [email protected] > www: forcetechnology.com > <https://forcetechnology.com?utm_source=mail-signature&utm_medium=email&utm_campaign=EmployeeBranding> > > ************************************************************************* > This email and any files transmitted with it may contain confidential > information intended for the addressee(s) only. The information is not to > be > surrendered or copied to unauthorised persons. If you have received > this communication in error, please notify us immediately by email at: > [email protected] > ************************************************************************* > > _______________________________________________ > Rtk-users mailing list > [email protected] > http://public.kitware.com/mailman/listinfo/rtk-users > > > _______________________________________________ > Rtk-users mailing list > [email protected] > http://public.kitware.com/mailman/listinfo/rtk-users > > > > > > > > > > >
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