which group number to use for private tags

Hi Mark

For private elements one shall use odd group numbers. Rules are very
clearly defined in part 5 of DICOM manuals:
==================================
It is possible that multiple implementors may define Private Elements
with the same (odd) group number. To avoid conflicts, Private Elements
shall be assigned Private Data Element Tags according to the following
rules.

a) Private Creator Data Elements numbered (gggg,0010-00FF) (gggg is
odd) shall be used to
reserve a block of Elements with Group Number gggg for use by an
individual implementor.
The implementor shall insert an identification code in the first unused
(unassigned) Element in this series to reserve a block of Private
Elements. The VR of the private identification code
shall be LO (Long String) and the VM shall be equal to 1.

b) Private Creator Data Element (gggg,0010), is a Type 1 Data Element
that identifies the
implementor reserving element (gggg,1000-10FF), Private Creator Data
Element (gggg,0011)
identifies the implementor reserving elements (gggg,1100-11FF), and so
on, until Private
Creator Data Element (gggg,00FF) identifies the implementor reserving
elements (gggg,FF00- FFFF).

c) Encoders of Private Data Elements shall be able to dynamically
assign private data to any
available (unreserved) block(s) within the Private group, and specify
this assignment through
the blocks corresponding Private Creator Data Element(s). Decoders of
Private Data shall be
able to accept reserved blocks with a given Private Creator
identification code at any position
within the Private group specified by the blocks corresponding Private
Creator Data Element.

Note: 1. The versions of this standard prior to V3.0 described shadow
groups. These
were groups with a group number one greater than the standard groups.
Elimination of conflicts in Private Data Element Tags have made this
distinction obsolete and this terminology has been retired.

2. The versions of this standard prior to V3.0 specified private group
element numbers (gggg,10FF-7FFF) reserved for manufacturers and private
group element numbers (gggg, 8100-FFFF) reserved for users. Elimination
of conflicts in Private Data Element Tags has made this distinction
obsolete and this specification has been retired.

d) Elements with Tags (0001,xxxx), (0003,xxxx), (0005,xxxx), and
(0007,xxxx) shall not be used. Since each Item within a sequence is a
self contained Data Set (see Section 7.5 on the nesting of Data Sets
via Sequences of Items), any Item which contains Private Data Elements
shall also have Private Creator Data Elements reserving blocks of
Elements for those Private Data Elements. The scope of the reservation
is just within the Item. Items do not inherit the Private Data Element
reservations made by Private Creator Data Elements in the Data Set in
which the Item is nested.

Note: 1. If a sequence is itself a Private Data Element and the Items
within the sequence also have Private Data Elements, then there will be
Private Creator Data Elements both outside the sequence and within the
sequence Items.
2. Different Items may reserve the same block of Private Data Elements
for different private creators. This is necessary to allow the nesting
of Data Sets collected from multiple sources into folders.
================================================

I hope this helps.

Regards
Bimalendu

markww wrote:[color=blue]
> Hi,
>
> Which group number should we use when we want to store private tags?
> I've been using group number:
>
> 0x3333
>
> for example, but I've seen group number:
>
> 0x0009
>
> used frequently as well. What rules should we follow when picking a
> private tag number for storage?
>
> Thanks,
> Mark[/color]