Hi all, I am attempting to forward project a CT volume (previously registered to a CBCT volume) using the geometry of a CBCT volume to generate raw projections. I also have access to the raw CBCT projections. I have used rktprojections to stack the raw CBCT projections and generate .mhd/raw files.
Next, I used rtkvariabprobeamgeometry on the scan.xml file that came with the raw CBCT projections to generate a RTK compatible geometry.xml file. Next, I have stacked the registered CT dicoms into a .mhd/raw format. The trouble I'm having is creating the projections using rtkforwardprojections. Specifically, I cannot find the correct transformmatrix in the CT header to tell rtkforwardprojetions the conversion from DICOM to IEC geometry. The output projections do not look like the raw projections I have from the CBCT. This may be a stupid question, but I cannot figure it out. From my own estimation, the transformation should be 1 0 0 0 0 -1 0 1 0 based on this diagram (https://www.semanticscholar.org/paper/nuclear-science-and-technology-Radiation-Quantities-Brink-McNitt-Gray/1ec27be3617dfc4e03bba86dcd92db8f3323de21/figure/3 [https://ai2-s2-public.s3.amazonaws.com/figures/2017-08-08/1ec27be3617dfc4e03bba86dcd92db8f3323de21/14-Figure1.4-1.png]<https://www.semanticscholar.org/paper/nuclear-science-and-technology-Radiation-Quantities-Brink-McNitt-Gray/1ec27be3617dfc4e03bba86dcd92db8f3323de21/figure/3> Figure 1.4 from nuclear science and technology Radiation Quantities and Units , Dose to the Patients , and Image Quality in Computed Tomography ( CT ) ( RAD UNITS ) Author : | Semantic Scholar<https://www.semanticscholar.org/paper/nuclear-science-and-technology-Radiation-Quantities-Brink-McNitt-Gray/1ec27be3617dfc4e03bba86dcd92db8f3323de21/figure/3> Figure 1.4 (left) The IEC patient coordinate system (the patient is lying in supine position); (right) transformation of coordinates between the IEC and DICOM coordinate systems [IEC, 2000] (cited in ICRU Report 71, 2004, page 35) - "nuclear science and technology Radiation Quantities and Units , Dose to the Patients , and Image Quality in Computed Tomography ( CT ) ( RAD UNITS ) Author :" www.semanticscholar.org ) My questions are: Is this the correct transformmatrix to apply? Do I need to also change the offset values in order to get the correct projections? Could this have something to do with the fact that I am using variant data? The .mhd for the registered CT is: ObjectType = Image NDims = 3 BinaryData = True BinaryDataByteOrderMSB = False CompressedData = False TransformMatrix = 1 0 0 0 0 -1 0 1 0 Offset = -131.03451538085938 -131.03451538085938 -91.809638977050781 CenterOfRotation = 0 0 0 AnatomicalOrientation = RAI ElementSpacing = 0.51285523409720002 0.51285523409720002 1.9958648681640625 DimSize = 512 512 93 ElementType = MET_DOUBLE ElementDataFile = CIRS_6A.raw Similarly, the .mhd for the raw CBCT projections is: ObjectType = Image NDims = 3 BinaryData = True BinaryDataByteOrderMSB = False CompressedData = False TransformMatrix = 1 0 0 0 1 0 0 0 1 Offset = -198.46200000000002 -148.798 0 CenterOfRotation = 0 0 0 AnatomicalOrientation = RAI ElementSpacing = 0.38800000000000001 0.38800000000000001 1 DimSize = 1024 768 501 ElementType = MET_FLOAT ElementDataFile = CIRS_6A_SCGH_P.raw Thank you kindly for your response, Brani
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