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matlabstructdicom

Write a struct into a DICOM header

I created a private DICOM tag and I would like to know if it is possible to use this tag to store a struct in a DICOM file using dicomwrite (or alike), instead of creating a field inside the DICOM header for each struct field.

(Something like saving a Patient's name, but instead of using a char data, I would use double)

Here is an example:

headerdicom = dicominfo('Test.dcm');
a.a = 1; a.b = 2; a.c = 3;
headerdicom.Private_0011_10xx_Creator = a;
img = dicomread('Test.dcm');
dicomwrite(img, 'test_modif.dcm', 'ObjectType', 'MR Image Storage', 'WritePrivate', true, headerdicom)

Undefined function 'fieldnames' for input arguments of type 'double'.

Thank you all in advance,

Solution

  • Depending on what "struct" means, here are your options. As you want to use a private tag which means no application but yours will be able to interpret it, you can choose the solution which is technically most appropriate. Basically your question is "which Value Representation should I assign to my private attribute using the DICOM toolkit of my choice?":

    1. Sequence: There is a DICOM Value Representation "Sequence" (VR=SQ) which allows you to store a list of attributes of different types. This VR is closest to a struct. A sequence can contain an arbitrary number of items each of which has the same attributes in the same order. Each attribute can have its own VR, so if your struct contains different data types (like string, integer, float), this would be my recommendation

    2. Multi-value attribute: DICOM supports the concept of "Value Multiplicity". This means that a single attribute can contain multiple values which are separated by backslashes. As the VR is a property of the attribute, all values must have the same type. If I understand you correctly, you have a list of floating point numbers which could be encoded as an array of doubles in one field with VR=FD (=Floating Point Double): 0.001\0.003\1.234... Most toolkits support an indexed access to the attributes.

    3. "Blob": You can use an attribute with VR=OB (Other Byte) which is also used for encoding pixel data. It can contain up to 4 GB of binary data. The length of the attribute tells you of how many bytes the attribute's value consists. If you just want to copy the memory from / to the struct, this would be the way to go, but obviously it is the weakest approach in terms of type-safety and correctness of encoding. You are going to lose built in methods of your DICOM toolkit that ensure these properties.

    To add a private attribute, you have to

    • reserve a range for the attribute specifying an odd group number and a prefix (2 hex digits) for the element numbers. (e.g. group = 0x0011, Element = 0x10xx) reserves a range from (0x0011, 0x10xx) - (0x0011, 0x10ff). This is done by specifying a Private Creator DICOM tag which holds a manufacturer name. So I suspect that instead of

      headerdicom.Private_0011_10xx_Creator = a;

    it should read e.g.

    headerdicom.Private_0011_10xx_Creator = "Gabs";
    • register your private tags in the private dictionary, most of the time by specifying the Private Creator, group, element and VR (one of the options above)

    Not sure how this can be done in matlab.