Digital Imaging and Communications in Medicine (DICOM)

5.6 DICOM Information Hierarchy 69
tify their data. For example, if two studies have the same Study Instance UID
value, they are expected to be identical, and contain identical sets of UIDs on the
Series and Image levels. Moreover, if two patients have the same Patient ID, they
are expected to be the same person. When properly used, this substantially improves
data identification. Otherwise, we can easily run into serious problems.
5.6.1
Problems with Patient ID
The use of Patient IDs was meant to eliminate obvious problems with using
patient names for patient identification. To put it simply, patient names are not
reliable for the following reasons:
1. They can be misspelled (letters, commas, even blanks between the name
parts).
2. They can be entered incorrectly (swapping first and last names, for example).
3. They can change (due to marriage, legal issues, and so on).
4. They can be hard to transliterate (typing foreign names on a DICOM unit
that does not support a specific foreign alphabet; consider entering Japanese
names on an English-based CT scanner, for example).
5. Their use can violate patient privacy.
With all this in mind, using an ID such as 12345XYZ to identify a specific patient
is obviously a much better approach. Nothing, however, comes without
problems in our real, imperfect world.
First of all, there is no central Patient ID repository that would generate
and maintain consistent Patient IDs. Nor are there universal ID rules. When
a patient shows up in a clinical center, it is always the center’s local policy that
assigns patient IDs, if any. Some would use a patient’s social security number,
date of birth, or anything else that is more or less patient-specific; in this case,
at least the same patient ID can be used consistently at the next patient encounter.
Others would simply use an alphanumeric code, or worse, a consecutive
numeral in attempt to make it more secure. This “security” makes the ID
location-specific (when it is impossible to use the same ID at another place)
and event-specific (perhaps at the same place but at a later time). Most facilities
would simply resort to using patient names as patient IDs, thus discarding the
whole idea of Patient IDs.
Moreover, some hospitals change Patient IDs depending on the modality
with which the patient was scanned, or the destination where the images had to
be sent for radiological reading. They easily end up with “123.ForDrSmith” and
“123.Followup” IDs, corresponding to the same 123 patient. Using those IDs
quickly turns into a total nightmare; despite their intended purpose, they would
never really identify anyone, at least not reliably. Furthermore, IDs are meant
for unique data identification, and not for encoding irrelevant information.