UIDs

private static string HashNameAndID(string name, string id)
{
	MD5 md5 = MD5.Create();	
	string s = name.Trim() + id.Trim();
	byte[] inputBytes = Encoding.ASCII.GetBytes(s);
	byte[] hash = md5.ComputeHash(inputBytes);
	
	// convert byte array to hex string
	StringBuilder sb = new StringBuilder();
	for (int i = 0; i < hash.Length; i++)
	sb.Append(hash[i].ToString("X2"));
	
	return sb.ToString().Substring(0, 8);
}

static List<Keyword> ItemsToAnonymise = new List<Keyword>()
{
	Keyword.OtherPatientIDs, Keyword.PatientAddress, Keyword.CountryOfResidence,
	Keyword.PatientTelephoneNumbers ,Keyword.MilitaryRank, Keyword.BranchOfService
};

public static DicomDataSetCollection Anonymise(string[] filesToAnonymise)
{
	Dictionary<string, string> UIDCache = new Dictionary<string, string>();
	DicomDataSetCollection results = new DicomDataSetCollection();
	Random random = new Random();
	string AccessionNumber = random.Next(1000000).ToString();
	string ReplacementValue = "Anonymised";
	
	// offset all dates by fixed amount (this leaves relative dates and ages correct
	TimeSpan dateoffset = new TimeSpan(random.Next(730) - 365, 0, 0, 0);

	foreach (string file in filesToAnonymise)
	{
		if (!DicomGlobal.IsDICOM(file))
		continue;
		
		DicomDataSet ds = new DicomDataSet(file);
		
		string hash = HashNameAndID(ds.Name, ds.PatientID);
		
		// Remove all private attributes
		ds.RemovePrivateAttributes();
		
		// replace all UIDs, except for known UIDs (i.e SOP Class UIDs)
		foreach (var attr in ds.Where(a => a.VR == "UI" 
				&& a.ExistsWithValue 
				&& !(a.Value.ToString().StartsWith("1.2.840.10008."))).ToList())
		{
			string UID = attr.Value as string;
			if (!UIDCache.ContainsKey(UID))
			UIDCache.Add(UID, DicomGlobal.NewUID());
			
			ds.Add(attr.KeywordCode, UIDCache[UID]);
		}

		// Replace all Names
		foreach (var attr in ds.Where(a => a.VR == "PN" && a.ExistsWithValue).ToList())
		ds.Add(attr.KeywordCode, ReplacementValue);
		
		// Replace all dates
		foreach (var attr in ds.Where(a => a.VR == "DA" && a.ExistsWithValue).ToList())
			ds.Add(attr.KeywordCode, (attr.Value as DateTime?)?.Add(dateoffset));
		
		// Anonymise some Patient Level Attributes
		ds.Add(Keyword.PatientName, hash);
		ds.Add(Keyword.PatientID, hash);
		ds.Add(Keyword.AccessionNumber, AccessionNumber);

		foreach (Keyword k in ItemsToAnonymise)
			if (ds[k].ExistsWithValue)
				ds.Add(k, ReplacementValue);

		// Try to add 4 white blocks around the image corners by modifying the pixel data
		// Designed to work with single frame images
		if (ds[Keyword.PixelData].Exists)
		{
			ushort bits = (ushort)ds[Keyword.BitsAllocated].Value;
			ushort rows = (ushort)ds[Keyword.Rows].Value;
			ushort columns = (ushort)ds[Keyword.Columns].Value;
			
			// set value to mid-scale
			int whiteValue = (1 << (bits - 1));
			float blockSize = 0.2F; // 20% of the image
			
			var pixels = ds[Keyword.PixelData].Value;
			
			if (pixels is ushort[,,])
			WriteBlockForAllFormats(ds, rows, columns, 
				(ushort)whiteValue, blockSize, (ushort[,,])pixels);
			else if (pixels is byte[,,])
			WriteBlockForAllFormats(ds, rows, columns, 
				(byte)whiteValue, blockSize, (byte[,,])pixels);
			
			ds.Add(Keyword.PixelData, pixels);
		}
		results.Add(ds);
	}
	return results;
}

private static void WriteBlockForAllFormats<T>(DicomDataSet ds, int rows, int columns, 
	T whiteValue, float blockSize, T[,,] pixel)
{
	//colour
	if ((ushort)ds[Keyword.SamplesPerPixel].Value == 3)
	{
		// by colour
		if ((ushort)ds[Keyword.PlanarConfiguration].Value == 0)
		{
			MakeBlocks(rows, columns * 3, whiteValue, blockSize, pixel, 0);
		}
		else // by plane
		{
			// like 3 mono images concatenated
			MakeBlocks(rows, columns, whiteValue, blockSize, pixel, 0);
			MakeBlocks(rows, columns, whiteValue, blockSize, pixel, rows);
			MakeBlocks(rows, columns, whiteValue, blockSize, pixel, rows * 2);
		}
	}
	else
	{
		// mono or palette (palette will give arbitrary colour, but will still be obscured)
		MakeBlocks(rows, columns, whiteValue, blockSize, pixel, 0);
	}
}

private static void MakeBlocks<T>(int rows, int columns, 
	T whiteValue, float blockThickness, T[,,] temp, int rowoffset)
{
	// top left
	for (int x = 0; x < columns * blockThickness; x++)
	for (int y = 0; y < rows * blockThickness; y++)
	temp[x, y + rowoffset, 0] = whiteValue;
	//top right
	for (int x = columns - 1; x > columns * (1 - blockThickness); x--)
	for (int y = 0; y < rows * blockThickness; y++)
	temp[x, y + rowoffset, 0] = whiteValue;
	//bottom left
	for (int x = 0; x < columns * blockThickness; x++)
	for (int y = rows - 1; y > rows * (1 - blockThickness); y--)
	temp[x, y + rowoffset, 0] = whiteValue;
	// bottom right
	for (int x = columns - 1; x > columns * (1 - blockThickness); x--)
	for (int y = rows - 1; y > rows * (1 - blockThickness); y--)
	temp[x, y + rowoffset, 0] = whiteValue;
}