Hi, Be aware that since the "object scanned always occupies the entire projection" you are dealing with the (difficult) interior problem. See, e.g., http://doi.org/10.1109/MSP.2010.936743. It's not surprising for this problem that FDK and SART give different answers. Best regards, Simon
On Fri, May 25, 2018 at 2:37 PM, <louis.go...@student.uliege.be> wrote: > Hi Cyril, > > Thank you for your fast response. > > The images are from a custom device in development by the X-RIS company > where I am currently doing an > internship in relation with my master thesis. However, due to the scanner > design (collimator and small field > of view) and the application, the type of object scanned always occupies > the entire projection. One aspect of > the application is to reconstruct object that nearly fit the scanner field > of view and therefore I do not have > other projections to show you except other ones of this kind. > > Indeed, we did not apply pre-processing to the projection to obtain > line-integrals. I will try this > solution. > > Thank you very much for your help, > Best regards, > > Louis > > ----- Mail original ----- > De: "Cyril Mory" <cyril.m...@creatis.insa-lyon.fr> > À: rtk-users@public.kitware.com > Envoyé: Vendredi 25 Mai 2018 17:43:41 > Objet: Re: [Rtk-users] rtkfdk and rtksart application input projection > type and voxel value range > > Hi Louis, > > You first need to get the projections right. RTK has a filter > "rtkProjectionsReader" to read projections exported from a scanner, and > apply all the necessary processing, including log-transform, to obtain > line-integrals. The reconstruction methods (rtkfdk, rtksart, ...) all > use line integrals as inputs, but they embed an rtkProjectionsReader, > which can do the conversion at runtime. However, if rtkProjectionsReader > does not recognize your data and applies the wrong processing, the > reconstruction methods will return garbage. So the safest way is to > first call the rtkProjectionsReader (using the command line tool > rtkprojections), look at its output, and make sure it looks like line > integrals: it must have near-zero values in air, and higher values in > dense objects. Only then can you start reconstructing. > > The diagram available here > http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionsReader.html shows > which processing is applied to which kind of data. The files in .mha > format are assumed to be line integrals already, and bypass all > processing, so it is probably not the format you should use. I do not > know which way .tif are processed, especially unsigned short .tif, but > I've had a look at your data, and it looks as if no log-transform is > applied on your projections. The borders of the projections, where > probably the rays have only gone through air, have high values. > Therefore, you're reconstructing a cylinder, as large as your > projections, which probably isn't what you want. > > Are you getting these images from a custom device built at the > university, or from a commercially available machine ? > > Do you have an acquisition where the object is clearly visible in the > projections ? If so, can you send over one of these projections ? > > Hope that helps, > > Cyril > > > On 25/05/2018 16:46, louis.go...@student.uliege.be wrote: > > Hi, > > > > I am currently using RTK for my Electrician Master's thesis and I am > finding some difficulties... > > > > We observed that reconstructed values range using fdk algorithm and sart > are different. How can this range be interpreted depending on the algortihm > used in order to compare the image quality between both algorithms? > > > > Furthermore, some voxels have negative value, is it possible to obtain > negative values with rtkfdk or rtksart application? does it make sens and > how can that be? > > > > And finally, last question, is there a specific projection file type > (.tif, .mha, ...) and/or pixel type (unsigned short, float, ...) to use > when using rtkfdk or rtksart? > > > > Here are some informations that may be useful: > > Object scanned: > > Rock sample and homogeneous polymer cylinder > > Projection are: > > -type: .tif (unsigned short) or .mha (float) > > -projection set: 360 seperated (.tif) files or 360 seperated (.mha) > files or one single (.mha) file > > > > Reconstructed image: > > -type: .mha (float) > > > > Algorithm used: > > -rtkfdk (without ramp filter) > > -rtksart (3~5 iterations, 1 projections processed between each update > of the reconstructed volume (1 for SART)) > > > > Here is a link to download some projection and reconstructed image: > > https://www.dropbox.com/sh/sgrzrylphe4dar2/ > AAAFW3hJYzyZGbPevf_CYteka?dl=0 > > > > Thanks in advance for your help or advices. > > > > Best regards, > > > > Louis > > _______________________________________________ > > Rtk-users mailing list > > Rtk-users@public.kitware.com > > https://public.kitware.com/mailman/listinfo/rtk-users > > _______________________________________________ > Rtk-users mailing list > Rtk-users@public.kitware.com > https://public.kitware.com/mailman/listinfo/rtk-users > _______________________________________________ > Rtk-users mailing list > Rtk-users@public.kitware.com > https://public.kitware.com/mailman/listinfo/rtk-users >
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