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Source to Axis Distance, Pixel per mm and measurements...?
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rickf
May 11, 2012, 1:26:39 PM5/11/12
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Hi,
I have a DRR Dicom image that has SAD = 1000, SID = 1000, pixels per mm = 0.9766 0.9766
and a c - arm Dicom Planar image of the same object from the same Gantry Angle that has SAD = 1000, SID = 1500, pixels per mm 0.388 0.388.
So, to align these images I would like to scale the DRR image up to the planar. However, using Matlab if I measure the number of pixels across an object of interest is in the DRR I get approximately 76. Multiply times 0.9766 and you get approximately 74 mm. The same object of interest in the Planar image is about 300 pixels across and that time 0.388 is approximately 116 mm. These are images of the same object, but clearly there's some kind of factor I'm not taking into account. Regardless that they are projections, the object should be the same "size" when pixels and resolution are taken into account? What am I missing....?
Thanks
Rick
I have a DRR Dicom image that has SAD = 1000, SID = 1000, pixels per mm = 0.9766 0.9766
and a c - arm Dicom Planar image of the same object from the same Gantry Angle that has SAD = 1000, SID = 1500, pixels per mm 0.388 0.388.
So, to align these images I would like to scale the DRR image up to the planar. However, using Matlab if I measure the number of pixels across an object of interest is in the DRR I get approximately 76. Multiply times 0.9766 and you get approximately 74 mm. The same object of interest in the Planar image is about 300 pixels across and that time 0.388 is approximately 116 mm. These are images of the same object, but clearly there's some kind of factor I'm not taking into account. Regardless that they are projections, the object should be the same "size" when pixels and resolution are taken into account? What am I missing....?
Thanks
Rick
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