Digital Imaging and Communications in Medicine (DICOM)

5.6 DICOM Information Hierarchy 67
file naming is justified: each DICOM image object includes the “Image SOP
Instance UID” attribute (0008,0018). This makes it a good name for a DICOM
image file. When you see file names such as:
1.2.804.114118.2.20040909.125423.3692976692.1.1.1
you are likely dealing with DICOM files. In essence, DICOM files are nothing
more than DICOM objects stored on your hard drive – DICOM object
memory dumps, if you wish.
UID parsing?
Even though UID names are always built with certain logic in mind, do not
try to parse them or use their names to convey additional information. For
example, even if you know that a UID name might include patient ID or
study date, do not try to extract this data. DICOM explicitly warns against
this.
UID names are not meant for any data exchange, and their sole purpose is
to distinguish between multiple object instances. As long as this is guaranteed,
the DICOM application is free to change or update UID names
as it finds appropriate with whatever additional naming logic it might be
using. In addition to what DICOM prescribes, correct UID-issuing policy
always remains on your DICOM manufacturer’s mind. They, through their
DICOM-compliant software, must track image changes and create a new
UID for each clinically different instance of the same image.
5.6
DICOM Information Hierarchy
Before we continue with our review of DICOM data, it is worth having a quick
look at how DICOM structures its information. Certainly, DICOM Data Dictionary
attributes play very important roles in mapping real-world data into
the DICOM standard. But still, these attributes are many. Don’t we need to put
them in some order?
This order is achieved in DICOM with the Patient-Study-Series-Image
hierarchy (Fig. 15):
1. One patient may have multiple studies.
2. Each study may include one or more image series.
3. Each series has one or more images.
This hierarchy naturally reflects what happens in the real world when a patient
needs to have some medical imaging done. John Smith comes to a hospital
where several studies may be scheduled (for example, MR, CT, and ultrasound
exams). Several follow-up studies could be needed later in time. Each study