title: How access to a single NumPy array in a DICOMDIR file with pydicom?
body: <p>I am using DICOM with Python and Pydicom library, when I have used .dcm files I hadn't problems. But I am using DICOMDIR data sets now. </p>
  
  <p>My code is the next:</p>
  
  <pre><code>ds = dicom.read_file("dicomdir")
  </code></pre>
  
  <p>I tried to access to the <code>pixel_array</code> elements as follows:</p>
  
  <pre><code>data = ds.pixel_array
  </code></pre>
  
  <p>And I get the next error: <code>TypeError: No pixel data found in this dataset.</code></p>
  
  <p>The output for <code>print ds</code> is more or less the next:</p>
  
  <p>(0004, 1130) File-set ID                         CS: 'GEMS_11_10_111'
  (0004, 1200) Offset of the First Directory Recor UL: 412
  (0004, 1202) Offset of the Last Directory Record UL: 412
  (0004, 1212) File-set Consistency Flag           US: 0
  (0004, 1220)  Directory Record Sequence   7 item(s) ---- 
     (0004, 1400) Offset of the Next Directory Record UL: 0
     (0004, 1410) Record In-use Flag                  US: 65535
     (0004, 1420) Offset of Referenced Lower-Level Di UL: 558
     (0004, 1430) Directory Record Type               CS: 'PATIENT'
     (0008, 0005) Specific Character Set              CS: 'ISO_IR 100'
     (0010, 0010) Patient's Name                      PN: '------------------'
     (0010, 0020) Patient ID                          LO: '246992'
     (0010, 0030) Patient's Birth Date                DA: '19630523'
     (0010, 0040) Patient's Sex                       CS: 'F'</p>
  
  <hr>
  
  <p>(0004, 1400) Offset of the Next Directory Record UL: 0
     (0004, 1410) Record In-use Flag                  US: 65535
     (0004, 1420) Offset of Referenced Lower-Level Di UL: 800
     (0004, 1430) Directory Record Type               CS: 'STUDY'
     (0008, 0005) Specific Character Set              CS: 'ISO_IR 100'
     (0008, 0020) Study Date                          DA: '20111011'
     (0008, 0030) Study Time                          TM: '151535.000000'
     (0008, 0050) Accession Number                    SH: '1009819901'
     (0008, 1030) Study Description                   LO: 'MG CONVENCIONAL'
     (0020, 000d) Study Instance UID                  UI: 1.2.840.113564.9.1.2005121220021252.20110608105548.21009819901
     (0020, 0010) Study ID                            SH: '1009819901'</p>
  
  <hr>
  
  <p>(0004, 1400) Offset of the Next Directory Record UL: 0
     (0004, 1410) Record In-use Flag                  US: 65535
     (0004, 1420) Offset of Referenced Lower-Level Di UL: 968
     (0004, 1430) Directory Record Type               CS: 'SERIES'
     (0008, 0005) Specific Character Set              CS: 'ISO_IR 100'
     (0008, 0060) Modality                            CS: 'MG'
     (0008, 103e) Series Description                  LO: 'Screen Save'
     (0020, 000e) Series Instance UID                 UI: 1.2.840.113619.2.144.2347322947.2192645372.5
     (0020, 0011) Series Number                       IS: '354'</p>
  
  <hr>
  
  <p>(0004, 1400) Offset of the Next Directory Record UL: 1298
     (0004, 1410) Record In-use Flag                  US: 65535
     (0004, 1420) Offset of Referenced Lower-Level Di UL: 0
     (0004, 1430) Directory Record Type               CS: 'IMAGE'
     (0004, 1500) Referenced File ID                  CS: ['DICOM', 'PA1', 'ST1', 'SE1', 'IM1']
     (0004, 1510) Referenced SOP Class UID in File    UI: Secondary Capture Image Storage
     (0004, 1511) Referenced SOP Instance UID in File UI: 1.2.840.113619.2.144.44653394.14990.1318380911.86
     (0004, 1512) Referenced Transfer Syntax UID in F UI: Explicit VR Little Endian
     (0008, 0005) Specific Character Set              CS: 'ISO_IR 100'
     (0008, 0008) Image Type                          CS: 'DERIVED'
     (0008, 0023) Content Date                        DA: '20111011'
     (0008, 0033) Content Time                        TM: '151909.000000'
     (0020, 0013) Instance Number                     IS: '8844'
     (0028, 0010) Rows                                US: 2298
     (0028, 0011) Columns                             US: 1980
     (0028, 1052) Rescale Intercept                   DS: '0'
     (0028, 1053) Rescale Slope                       DS: '1'</p>
  
  <hr>
  
  <p>The last part is repeated four times. I have 4 images in my DICOMDIR dataset.</p>
  
  <p>Do you know how access to the field with the Numpy Array for each image?</p>