Empty Sequences - DICOM

This is a discussion on Empty Sequences - DICOM ; There is some discrepencies at my office on this topic. We are creating an empty Sequence because it may be a Type 2. I reviewed the standard and historical emails in this newsgroup. I was not able to put the ...

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Thread: Empty Sequences

  1. Empty Sequences

    There is some discrepencies at my office on this topic. We are
    creating an empty Sequence because it may be a Type 2. I reviewed the
    standard and historical emails in this newsgroup. I was not able to
    put the pieces together to satisfy my curiosity. What are the accepted
    encodings of an Empty Sequence?

    Is the following valid?
    0040 0555 5153 0000 FFFF FFFF //0040, 0555|SQ|-1
    FFFE E000 FFFF FFFF //Item Tag|-1
    FFFE E00D 0000 0000 //Item Delimiter
    Tag
    FFFE E0DD 0000 0000 //Sequence
    Delimiter Tag

    Is the following valid?
    0040 0555 5153 0000 0000 0000 //0040, 0555|SQ|0

    What are other valid possibilities?

    Thank you.

    Bill


  2. Re: Empty Sequences

    Bill wrote:
    > There is some discrepencies at my office on this topic. We are
    > creating an empty Sequence because it may be a Type 2. I reviewed the
    > standard and historical emails in this newsgroup. I was not able to
    > put the pieces together to satisfy my curiosity. What are the accepted
    > encodings of an Empty Sequence?
    >
    > Is the following valid?
    > 0040 0555 5153 0000 FFFF FFFF //0040, 0555|SQ|-1
    > FFFE E000 FFFF FFFF //Item Tag|-1
    > FFFE E00D 0000 0000 //Item Delimiter
    > Tag
    > FFFE E0DD 0000 0000 //Sequence
    > Delimiter Tag
    >
    > Is the following valid?
    > 0040 0555 5153 0000 0000 0000 //0040, 0555|SQ|0
    >
    > What are other valid possibilities?


    Hi Bill,

    Not sure why you are doing this. But I believe you are missing case
    #2, see p42 from PS 3.5 (Table 7.5.2). You should be able to define
    your Item with a fixed length too, right ?

    -M


  3. Re: Empty Sequences

    Hi Bill

    Empty sequences have to be empty.

    No items in them. Nothing.

    There are two ways to encode them.

    Either a VL of 0.

    Or a VL of 0xFFFFFFFF followed immediately by a Sequence Delimiter Tag.

    So your first example is wrong because there is an Item in there;
    this will lead to a host of error messages from a validator because
    most of the attributes required in the definition of the item will
    be missing but some are type 1.

    Your second example is correct.

    This would be the (ONLY) other correct way:

    0040 0555 5153 0000 FFFF FFFF //0040, 0555|SQ|-1
    FFFE E0DD 0000 0000 //Sequence
    Delimiter Tag

    There is nothing "accepted" about this; that is the way it is
    defined in the standard; any other way is wrong.

    David

    PS. Mathieu's response is incorrect ... there should be no item
    in the first place hence how an Item's VL is encoded is irrelevant.

    Bill wrote:
    > There is some discrepencies at my office on this topic. We are
    > creating an empty Sequence because it may be a Type 2. I reviewed the
    > standard and historical emails in this newsgroup. I was not able to
    > put the pieces together to satisfy my curiosity. What are the accepted
    > encodings of an Empty Sequence?
    >
    > Is the following valid?
    > 0040 0555 5153 0000 FFFF FFFF //0040, 0555|SQ|-1
    > FFFE E000 FFFF FFFF //Item Tag|-1
    > FFFE E00D 0000 0000 //Item Delimiter
    > Tag
    > FFFE E0DD 0000 0000 //Sequence
    > Delimiter Tag
    >
    > Is the following valid?
    > 0040 0555 5153 0000 0000 0000 //0040, 0555|SQ|0
    >
    > What are other valid possibilities?
    >
    > Thank you.
    >
    > Bill
    >


  4. Re: Empty Sequences

    Thank you David. This is the confirmation I needed.

    bill


  5. Re: Empty Sequences

    Thank you David. This is the confirmation I needed.

    bill


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