What's on a Hospital Scan CD: DICOMDIR, Folders and the Viewer

Open a scan CD in your file manager and it looks oddly old-fashioned: capital letters, short names, no extensions. That’s on purpose. The DICOM standard defines how images go on a disc, so a CD burned by one hospital can be read by another’s system.

The parts of a scan CD

A typical disc looks like this:

DICOMDIR
DICOM/
  ST000000/
    SE000000/
      IM000000
      IM000001
      ...
VIEWER.EXE
AUTORUN.INF

Names and folders differ between hospitals, but the pieces are the same.

DICOMDIR: the index

Every DICOM disc must have a file called DICOMDIR at the top. It lists what’s on the disc as a tree:

• Patient → Study (one visit or exam) → Series (one set of images, such as one reconstruction) → Image (one file).

Each image record points to its file. A viewer or a hospital system reads the DICOMDIR to show the whole disc at once, without opening every file first.

You can read it yourself with the free OFFIS DICOM Toolkit (DCMTK):

dcmdump DICOMDIR

Look for DirectoryRecordType (PATIENT, STUDY, SERIES, IMAGE) and ReferencedFileID, the path to each file, written with backslashes, like DICOM\ST000000\SE000000\IM000000.

The image files

The standard keeps paths simple: each part of a file’s name is at most eight characters, there are at most eight levels of folders, and there’s no extension. So IM000001 is a complete DICOM file, not a broken one.

One file is usually one image (one CT slice), though some files hold a whole clip, like an ultrasound loop.

The viewer and AUTORUN.INF

Most discs also carry a viewer program so you can look without installing anything. It’s nearly always a Windows program, and AUTORUN.INF tells Windows which file to start. That’s why the disc seems to “work” on Windows and not on a Mac. See how to open a scan CD on a Mac and on Windows.

Sometimes it’s a ZIP

Many discs, and nearly every download from a patient portal, hold the images as a ZIP file instead of loose folders. Inside is the same structure: a DICOMDIR, the folders and the image files. Our viewer opens the ZIP itself; there’s no need to unzip it first.

Opening the whole disc

Copy the disc to a folder, then open the folder (or the ZIP) in a DICOM viewer. Our browser viewer reads the image files, skips the DICOMDIR and the viewer program, and shows the largest series first. Nothing is uploaded.

Key takeaways

• DICOMDIR is the disc’s index: patient, study, series, image.
• File names are short and have no extension by design.
• The viewer on the disc is a convenience, usually Windows-only; the images don’t need it.
• Many discs and downloads hold all this inside one ZIP, which opens directly in the viewer.
• dcmdump DICOMDIR shows what’s on a disc.

Open a copied scan CD in the browser →

Run a practice or an imaging center? We’re glad to share what we know. When you want a portal that makes all of this easy for your patients, we’ll build it for you, and because we work with AI-assisted development, it costs far less than you might expect. Let’s talk.