Dicom UUID-derived UID generator

DicomUID.cs

    // A port from javascript: https://hcintegrations.ca/2014/05/14/quick-and-dirty-javascript-dicomweb-uid-generator/
    public static string NewUID_dirty()
    {
        var r = new System.Random();
        var uid = System.Text.RegularExpressions.Regex.Replace("2.25.xxxxxxxxxxxx4xxxyxxxxxxxxxxxxxxx", "x", m => (r.Next()%16).ToString() );
        return System.Text.RegularExpressions.Regex.Replace(uid, "y", m => (r.Next()&3|8).ToString());
    }

    // Trying to strictly follow the Dicom spec: ftp://medical.nema.org/medical/dicom/2013/output/html/part05.html#sect_B.2
    // More details at: ISO/IEC 9834-8 / ITU-T X.667, Section 6.3
    public static string NewUID()
    {
        var guid = new System.Guid().ToByteArray();
        var bigint = new System.Numerics.BigInteger(guid);
        return "2.25." + bigint.ToString();
    }