[Insight-developers] DICOM UID generation

[David Clunie]

Hi Jim

Sending money to ANSI is a complete waste of money, since there are
free UID roots available, and nobody cares where your root comes from
as long as it is unique.

For other alternatives, see:

"http://www.dclunie.com/medical-image-faq/html/part8.html#UIDRegistration"

Your biggest problem though is not getting a root, it is making sure
that every file generated by ITK anywhere no matter where and by whom
it is installed is globally unique.

Typically this is done with something unique to the device on which it
is installed, e.g. serial number, hostid, MAC address or similar, as
well as any process or thread running on that device (e.g. process
number). It is very hard to get this right in a multi-platform toolkit.
The MAC address, process number, a date time stamp with high precision
and a random number might be necessary. If it won't all fit into 64
bytes, considering feeding everything (after the root) into some sort
of cryptographic hash function.

The question also always arises as to whether it is safer to require the
installer/user of a toolkit to acquire and install their own root rather
than use the same one supplied to all users of the toolkit. In general
it is extremely hard to guarantee that all instances of the toolkit
compiled and installed anywhere on any platform will generate unique IDs.
Conversely, it is hard to get users of toolkits to do the right thing.

Having accounted for that problem, another is to be sure that not only
are all generated images assigned a unique SOP Instance UID, but that if
they are part of the same (new) series, they must have a new unique Series
Instance UID that is the same for all images in that Series. Same goes
for the Study Instance UID, though you can add to an existing study, but
not to an existing series unless you are the equipment that created that
series in the first place. Same goes for Frame of Reference UID, which
obviously needs a lot of attention in a registration toolkit !

Typical mistakes generating UIDs, by the way, are to exceed 64 bytes total,
and to use leading zeroes in numeric components, both of which are illegal
and cause significant problems downstream.

The formal rules are in PS 3.8 Annex F and PS 3.5 Section 6.1 and ISO 8824.

There are a few more comments of mine in the FAQ at:

"http://www.dclunie.com/medical-image-faq/html/part2.html#UID"

David


Miller, James V (Research) wrote:

> With the addition of GDCM to ITK, we can now write DICOM files.  However, we
> have no mechanism for generating the UIDs that are needed within a DICOM
> file. From what I can see, these UIDs are be thought of being composed of a
> prefix and suffix.  The prefix is assigned to an organization by some
> governing body.  The suffix is something unique that ITK (or GDCM) would
> have to generate.  Usually the suffix is a combination of a device number,
> device type (for ITK, perhaps a secondary capture device or an imaging
> workstation), a datestamp, etc. The rules of DICOM indicate the suffix is
> NOT TO BE PARSED to determine any information (for instance slice number).
>  
> The prefix is composed of a set of numbers that identify the organization,
> the granting organization, and the country of origin.  For ITK, we could
> have an organization number assigned by ANSI. Below is a link to ANSI site
> on this matter.  ANSI will grant a numeric and/or an alphanumeric
> identifier.  To write DICOM files, we need the numeric identifier.  The cost
> for a numeric identifier is $1000. Is enough of the legal entity of the
> Insight Software Consortium established that we could request a numeric
> organization number from ANSI?
>  
> http://www.ansi.org/other_services/registration_programs/reg_org.aspx?menuid
> =10
> <http://www.ansi.org/other_services/registration_programs/reg_org.aspx?menui
> d=10> 
>  
> There are some "free" alternatives for getting a unique organization number.
> There are people who have organization numbers that are willing to grant a
> subspace of their number to other organizations. There are also some
> European organizations that may grant a unique organization number free of
> charge.
>  
> Given that ITK was developed under NIH resources, I think we should go the
> ANSI route to obtaining an organization number.
>  
> My understanding of the DICOM UID process is based on a few minutes of
> google searches, so I may be off base.  If anyone knows anything in more
> detail, please speak up.
>  
>  
>  
> 
> Jim Miller 
> _____________________________________
> Visualization & Computer Vision
> GE Research
> Bldg. KW, Room C218B
> 1 Research Circle, Schenectady NY 12309-1027
> 
> millerjv at research.ge.com <mailto:millerjv at research.ge.com> 
> 
> james.miller at research.ge.com
> (518) 387-4005, Dial Comm: 8*833-4005, 
> Cell: (518) 505-7065, Fax: (518) 387-6981