Hi there!

In FHIR, unlike HL7 v2, coding systems are defined as URIs which makes them quite long. Certainly longer than an SH can hold.

For example in HL7v2 "LN" would represent the LOINC coding system, but in FHIR it would be "http://loinc.org/" which does happen to just fit in an SH but most do not.

For the standard coding systems, it would be easy enough to map them. But for local systems that's not practical.

I have been researching how to map these through to DICOM and while there is Long Code Value there is no tag to represent a longer Coding Scheme Designator (system).

Is there any advice from the community on the best way to go about this, or is this just a current incompatibility between FHIR and DICOM?

Thanks

Hi Ben

The only standard coding schemes that should be used in DICOM CodingSchemeDesignator are those listed in the PS3.16 table:

http://dicom.nema.org/medical/dicom/current/output/chtml/part16/chapter_8..html

or if not present there, then those in HL7 V2 Table 0396, the latest release of which seems to be here:

http://terminology.hl7.org/5.1.0/CodeSystem-v2-0396.html

I.e., do not ever send "http://loinc.org/" instead of "LN".

If you are mapping from FHIR, you need to lookup the correct DICOM (or HL7 V2) value to use.

If the FHIR coding system URI you are mapping from is unrecognized, unless there is something usable in "https://www.hl7.org/fhir/codesystem-definitions.html#CodeSystem.identifier, you need to make up a private short string to use that starts with "99"; if you are maintaining a local coding scheme for use in FHIR and DICOM you need to supply both a URI and a 99 short string code.

If there is a commonly used standard coding scheme that gets added to FHIR that is not already in DICOM PS3.16 Table 8-1 and/or HL7 V2 Table 0396, we can consider adding it with a CP.

To re-iterate, DO NOT EVER ENCODE A URI IN DICOM CodingSchemeDesignator, whether it comes from FHIR or any place else, not because it may be too long, but because it does not satisfy the rules for permissible content.

I have not seen any clear advice from HL7 folks mapping V2 messages using Table 0396 and/or private coding schemes back and forth from FHIR, but if you find it, let us know.

David

On Wednesday, May 17, 2023 at 11:45:57 PM UTC-4, Ben Ganley wrote:
> Hi there!
>
> In FHIR, unlike HL7 v2, coding systems are defined as URIs which makes them quite long. Certainly longer than an SH can hold.
>
> For example in HL7v2 "LN" would represent the LOINC coding system, but in FHIR it would be "http://loinc.org/" which does happen to just fit in an SH but most do not.
>
> For the standard coding systems, it would be easy enough to map them. But for local systems that's not practical.
>
> I have been researching how to map these through to DICOM and while there is Long Code Value there is no tag to represent a longer Coding Scheme Designator (system).
>
> Is there any advice from the community on the best way to go about this, or is this just a current incompatibility between FHIR and DICOM?
>
> Thanks

On Friday, May 19, 2023 at 8:08:02 PM UTC+12, David Clunie wrote:
> Hi Ben
>
> The only standard coding schemes that should be used in DICOM CodingSchemeDesignator are those listed in the PS3.16 table:
>
> http://dicom.nema.org/medical/dicom/current/output/chtml/part16/chapter_8..html
>
> or if not present there, then those in HL7 V2 Table 0396, the latest release of which seems to be here:
>
> http://terminology.hl7.org/5.1.0/CodeSystem-v2-0396.html
>
> I.e., do not ever send "http://loinc.org/" instead of "LN".
>
> If you are mapping from FHIR, you need to lookup the correct DICOM (or HL7 V2) value to use.
>
> If the FHIR coding system URI you are mapping from is unrecognized, unless there is something usable in "https://www.hl7.org/fhir/codesystem-definitions.html#CodeSystem.identifier, you need to make up a private short string to use that starts with "99"; if you are maintaining a local coding scheme for use in FHIR and DICOM you need to supply both a URI and a 99 short string code.
>
> If there is a commonly used standard coding scheme that gets added to FHIR that is not already in DICOM PS3.16 Table 8-1 and/or HL7 V2 Table 0396, we can consider adding it with a CP.
>
> To re-iterate, DO NOT EVER ENCODE A URI IN DICOM CodingSchemeDesignator, whether it comes from FHIR or any place else, not because it may be too long, but because it does not satisfy the rules for permissible content.
>
> I have not seen any clear advice from HL7 folks mapping V2 messages using Table 0396 and/or private coding schemes back and forth from FHIR, but if you find it, let us know.
>
> David
> On Wednesday, May 17, 2023 at 11:45:57 PM UTC-4, Ben Ganley wrote:
> > Hi there!
> >
> > In FHIR, unlike HL7 v2, coding systems are defined as URIs which makes them quite long. Certainly longer than an SH can hold.
> >
> > For example in HL7v2 "LN" would represent the LOINC coding system, but in FHIR it would be "http://loinc.org/" which does happen to just fit in an SH but most do not.
> >
> > For the standard coding systems, it would be easy enough to map them. But for local systems that's not practical.
> >
> > I have been researching how to map these through to DICOM and while there is Long Code Value there is no tag to represent a longer Coding Scheme Designator (system).
> >
> > Is there any advice from the community on the best way to go about this, or is this just a current incompatibility between FHIR and DICOM?
> >
> > Thanks
Hi David,

Thanks for taking the time to give this advice.

Will go down the route of maintaining some mapping tables.

Many thanks,
Ben