How to read a tag from a subheader

[marcelzwiers]

If I read a DICOM dataset and display it I see a field that I want to read, i.e. I want to read (0021, 1106) from this dataset:

ds
[..]
      ---------
   (0021, 0011) Private Creator                     LO: 'SIEMENS MR SDI 02'
   (0021, 11fe)  Private tag data  1 item(s) ---- 
      (0021, 0011) Private Creator                     LO: 'SIEMENS MR SDI 02'
      (0021, 1103) Private tag data                    DS: '105060.0'
      (0021, 1104) Private tag data                    DS: '0.2475'
      (0021, 1106) Private tag data                    LO: 'X_1_1_1_1_1_1_34_1_1_68_1_114'
[..]

I get a key error if I try:

ds[(0x21, 0x1106)]
Traceback (most recent call last):
  File "/home/marzwi/bin/miniconda3/envs/bidscoin/lib/python3.12/site-packages/IPython/core/interactiveshell.py", line 3553, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-40-af69ca584a58>", line 1, in <module>
    dicomdata[(0x21, 0x1106)]
    ~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/home/marzwi/bin/miniconda3/envs/bidscoin/lib/python3.12/site-packages/pydicom/dataset.py", line 914, in __getitem__
    elem = self._dict[tag]
           ~~~~~~~~~~^^^^^
KeyError: (0021, 1106)

The only way I manage to read the tag is by using iterall(), but isn't there a better way?

    tagname = '(0021,1106)'
    for elem in ds.iterall():
        if tagname in (elem.name, elem.keyword, str(elem.tag), str(elem.tag).replace(', ',',')):
            value = elem.value
            break

[scaramallion]

I'm assuming you figured it out, but for anyone else the required element is nested inside at least one sequence with tag (0021,11FE). To access elements in a sequence you need to do:

seq = ds[0x0021, 0x11FE] # A sequence item, which is basically list[Dataset]
item = seq[0]  # The first Dataset item in the sequence, there may be 0 or more items
elem = item[0x0021, 0x1106]  # The required element
# elem = ds[0x0021, 0x11FE][0][0x0021, 0x1106]  # Alternatively
value = elem.value  # The value of the required element

All the above is for private elements (those with an odd group number), for public elements you can also access via the more human friendly keywords:

value = ds.BeamSequence[0].BeamName  # The value of the Beam Name element

[marcelzwiers]

Yes, thanks, I indeed figured it out. I printed the ds but because the new enhanced DICOM from Siemens (XA-30) is so long and repetitive, which made that the root element was scrolled out of my screen completely (so I missed it when I did what you described here, and got an error).