[Insight-users] Similarity3Dtransform: Scale value interpretation

[Emma Ryan]

Hi,

  I am using the itk Similarity3DTranform to obtain a registration between two volumes. 
Dataset1 : 512 x 512 x 30 (Resolution = 0.684 x 0.684 x 1.0) :  Image Patient Position : -175, -175, 125 (from dicom header)
Dataset2: 512 x 512 x 30 (Resolution = 1.0 x 1.0 x 1.0 ) : Image Patient Position: -255, -255, 101 (from dicom header)

Both are of the same modality (CT). 

I have a few questions.

1. How does one interpret the scale value of  (-0.00008). What does negative mean ?  Division ?

2. Prior to registration I mention the size, origin and spacing for both the fixed and moving volumes. At resampling, the moving volume are resampled to match the spacing and origin of the fixed volume. So should I care to include the scale transform in my registration/optimization parameters ?

3. Does resampling take care of the resolution difference ?

4. Is it necessary that I set the initial scaling to 1.428 to compensate for the resolution ?

5. Dicom images have Image Patient Postion tag. Is this the information that goes into the  "Origin" variable ?  If not, where do I get the image origin information ?

I have read a lot of literature on resampling and all the pdfs and ppts on ITK, but I fail to understand these.

Please help !

Emma




       
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