ITK ResampleDicom

1
votes

I was trying the ResampleDicom example and noticed that for CT it changes the rescaleintercept value as well as the rescaletype.

Any particular reason why it does this?

Thanks,

1
dicomitkresampling
I think for CT, you have Hounsfield units and signed pixel intensities. What is the new rescaleType after running the example, and are the pixel intensities still signed, or are they perhaps "normalized" to an unsigned range? - Chris O
The original CT rescaletype is HU, the modified rescalteype is US. Pixel Representation is 1 (signed) in the original image and 0 (unsigned) in the new image. The Pixel Padding Value also changes from 63536 to 13110\13109\54 but not sure if it has to do with the whole thing - Matimont

1 Answers

2
votes

According to DICOM standard “the Modality LUT IE defines the Attributes that describe the transformation of manufacturer dependent pixel values into pixel values which are manufacturer independent (e.g. Hounsfield units for CT, Optical Density for film digitizers, etc.). When the transformation is linear, the Modality LUT is described by Rescale Slope (0028,1053) and Rescale Intercept (0028,1052)."

Modality LUT linear transformation is calculated as: Output units = m*SV + b Where, SV = stored values, m= Rescale Slope and b = Rescale Intercept

The Rescale Type (0028,1054) specifies the output units after the Modality LUT transformation. In your case, rescale type "US" means unit is unspecified. Also, Rescale Type "HU" is used for Hounsfield Units (CT) and "OD" for Optical Density.

If output files Pixel Representation value is set to 1, this means the stored image data is signed or the output image data will be signed after the Modality LUT transformation.

Also your resultant DICOM image should have single value for Pixel Padding Value (0028,0120) attribute. DICOM standard defines value multiplicity for this tag as 1 and it should not have 3 values such as "13110\13109\54". A range of pixel padding values to suppressed should be specified by combination of Pixel Padding Value (0028,0120) and Pixel Padding Value Range Limit (0028,0121). Please refer to DICOM standard PS 3.3 section C.7.5.1.1.2 for more information about the use of pixel padding.

So, it is possible that Modality LUT transformation was applied to the image data as part of the resampling process.