1. Entry
     SOP Instance Observation (2.16.840.1.113883.10.20.6.2.8)
    1. Entry
       Purpose of Reference Observation (2.16.840.1.113883.10.20.6.2.9)
    2. Entry
       Referenced Frames Observation (2.16.840.1.113883.10.20.6.2.10)
      1. Entry
         Boundary Observation (2.16.840.1.113883.10.20.6.2.11)