Validating DICOM File

Question

I have to pick all valid DICOM Files from folder. I can recursively pick all the files from the folder which have *.DCM extension. But any file with *.DCM also picked up and such file is not valid DICOM File.

What is best way.

I thought of reading few byte of the file and validating.

Or

Any Other Method or any other EXEs we have which validates.

Thank you, Harsha

Edit: Solution for the problem: I finally used the dcmftest.exe for verification. Hope I am on right track. -Harsha

Answer 1

You want to recognize DICOM files, not to validate. There is big difference. Validation means (at least!) that all the tags required for its SOP class are present.

Recognition is easy, as the DICOM file has to contain text DICM at the offset 0x80, so that tags start at the offset 0x84 of file.

Note that sometimes only the serialized dataset is stored (starting with tag group 8 at file offset 0), and these are more difficult to recognize, but are not standard.

EDIT: As an example, consider a RAR archive. It's easy to recognize, because it starts with Rar!. However, to be sure that it's a valid RAR archive, you have to decompress all the files and check their CRCs, and this is something that could be done only by RAR itself (and it's slow).

Answer 2

I know this has been answered already but I had a similar requirement, so I whipped up some extension methods to do exactly that. Works on Files, FileStreams, MemoryStreams and generic Streams. Only reads the specific 4 bytes needed to validate the filetype. Extremely efficient, I was able to run through thousands of files within seconds.

C#

public static class Dicom
{
    public static bool IsDicomFile(this Stream s)
    {
        //Create an empty 4 byte array
        byte[] dba = new byte[4];

        //Seek to 0x80
        s.Seek(128, SeekOrigin.Begin);

        //Read the following 4 dba
        s.Read(dba, 0, 4);

        //Compare to 'DICM'
        return dba.SequenceEqual(new byte[4] {68, 73, 67, 77});
    }

    public static bool IsDicomFile(this MemoryStream ms)
    {
        return ((Stream)ms).IsDicomFile();
    }

    public static bool IsDicomFile(this FileStream fs)
    {
        return ((Stream)fs).IsDicomFile();
    }

    public static bool IsDicomFile(this FileInfo fi)
    {
        return fi.OpenRead().IsDicomFile();
    }
}

VB.NET

<Extension()> _
Public Function IsDicomFile(ByVal s As Stream) As Boolean
    'Create an empty 4 byte array
    Dim dba() As Byte = New Byte(3) {}

    'Seek to 0x80
    s.Seek(128, SeekOrigin.Begin)

    'Read the subsequent 4 bytes
    s.Read(dba, 0, 4)

    'Compare to 'DICM'
    Return dba.SequenceEqual(New Byte(3) {68, 73, 67, 77})
End Function

<Extension()> _
Public Function IsDicomFile(ByVal ms As MemoryStream) As Boolean
    Return DirectCast(ms, Stream).IsDicomFile
End Function

<Extension()> _
Public Function IsDicomFile(ByVal fs As FileStream) As Boolean
    Return DirectCast(fs, Stream).IsDicomFile
End Function

<Extension()> _
Public Function IsDicomFile(ByVal fi As FileInfo) As Boolean
    Return fi.OpenRead().IsDicomFile
End Function