I am working with DICOM images, and would like to change the resolution of all the images I have to 0.5mm/pixel. What are the entries that I should access in the DICOM header and how can I change the resolution? Note that my header does not contain 'PixelSpacing'.
Thanks a lot for your response. It is very helpful.
I am working with MATLAB actually, and I think it is very interesting what you said about adding a PixelSpacing entry to the header. Could you please give me further indications on how I could do that as my images do not have original information on the spatial resolution apparently? What value would PixelSpacing take in this case?
Moreover, I could not find your e-mail address.
Thanks again,
Vera
Hi Vera,
What type of images are yours? There should be something in there somewhere to relate the pixel size to the object, which will depend on the manufacturer of the file, and also the software the file was written from. But if not you could add PixelSpacing to the header, which may or may not help you. Are you planning to upload the images to some processing software?
If you read the file into Matlab (inf=dicominfo('file.dcm');) then you can add a tag like this:
inf.PixelSpacing(1,1)=0.5; %x resolution
inf.PixelSpacing(2,1)=0.5; %y resolution
This is of course assuming that the resolution is the same in both directions and of course that you know the resolution of the images is exactly 0.5 mm/pixel!
Hi Jim,
Thanks a lot for your answer.
I am working on echocardiographic images. I have a large database where I have to adjust all resolutions to 0.5 mm/pixel. That's exactly my concern: If I am going to add the PixelSpacing tag myself, I would have to assume the values, whereas, in my case, I need to know the values and adjust them so that all my images would have the same resolution before I start analyzing and treating them.
Thanks,
Vera
Vera,
Both Matlab and ITK offer methods to resample a volume from one spacing to another. But the question I would have is, how do you know the pixel spacing of the original image?
- Wes
Vera,
The dicom VR PixelSpacing is not necessarily used to put the information about pixel-sizes... Yeah, very confusing, but it depends on modality and sometimes the manufacturer also.
Dicom VR's that I encountered, containing pixel-size information are:
- 0x0028 0x0030 PixelSpacing
- 0x3002 0x0011 ImagePlanePixelSpacing
- 0x0018 0x602c PhysicalDeltaX
- 0x0018 0x602e PhysicalDeltaY
- 0x0018 0x1164 ImagerPixelSpacing
- 0x200d 0x3303 Philips volume scan (Private)
For example in angiography, ImagerPixelSpacing is used to define the pixelsize of the detector. If you use that, in combination with a magnification factor depending on X-ray source to detector distance, and X-ray source to patient distance (average), you can calculate a more meaningful pixel-size than that of the detector.
I also want to advise you to create NEW dicom objects, with the resolution and header-info you want, instead of messing with the originals.
If you upload a sample echo cardiac image, I can take a look where the desired information is hidden.
Hi Vera, check your DICOM Header and see if you can find 0018 1100 Reconstruction Diameter or 0018 1149 FOV Dimensions. If you combine this information with 0028 0010 Rows and 0028 0011 Columns you can simply divide the image dimensions by the number of pixels in that direction to calculate the pixel size in the image.
*** Resolved ***
The information was in PhysicalDeltaX, PhysicalDeltaY, PhysicalUnitsXDirection and PhysicalUnitsYDirection, all encapsulated in a SequenceOfUltrasoundRegions.