How to generate SOPInstance UID for DICOM file?

Question

I am developing a system which will be able to create structured report for PACS.

Obviously in order to create a DICOM instance (file containing Report data), I need three UIDs for Study, Series and Instance. StudyUID and SeriesUID must be the same as that of study and series that report is created for. But for SOPInstanceUID, I need to generate new UID.

I have seen getNewSOPInstanceUID method in Pixelmed documentation, but I am not familiar with the Pixelmed source. I need an algorithm or Python source.

Answer 1

There are 2 ways in DICOM to create UIDs. One based on a registered UID root and one based on a UUID. The later method was added to the DICOM standard with CP-1156 in 2012. UIDs for things like Study UID, Series UID, SOP Instance UID can be created by converting a UUID to a DICOM UID.

Most programming languages have build in support to create a UUID. The sample code code below creates a valid DICOM UID in C# based on a GUID value.

public static string GuidToUidStringUsingStringAndParse(Guid value)
{
    var guidBytes = string.Format("0{0:N}", value);
    var bigInteger = BigInteger.Parse(guidBytes, NumberStyles.HexNumber);
    return string.Format(CultureInfo.InvariantCulture, "2.25.{0}", bigInteger);
}

The following method does the same but is about 5 times faster:

public static string ConvertGuidToUuidInteger(ref Guid value)
{
    // ISO/IEC 9834-8, paragraph 6.3 (referenced by DICOM PS 3.5, B.2) defines how
    // to convert a UUID to a single integer value that can be converted back into a UUID.

    // The Guid.ToByteArray Method returns the array in a strange order (see .NET docs),
    // BigInteger expects the input array in little endian order.
    // The last byte controls the sign, add an additional zero to ensure
    // the array is parsed as a positive number.
    var octets = value.ToByteArray();
    var littleEndianOrder = new byte[]
    { octets[15], octets[14], octets[13], octets[12], octets[11], octets[10], octets[9], octets[8],
        octets[6], octets[7], octets[4], octets[5], octets[0], octets[1], octets[2], octets[3], 0 };

    return "2.25." + new BigInteger(littleEndianOrder).ToString(CultureInfo.InvariantCulture);
}