What is a .dcm file and how to open it
A .dcm file is a medical image: a CT, MRI, X-ray or ultrasound frame. Ordinary picture apps cannot open it. Here is what it holds and how to view it.
What is inside a .dcm file
DICOM is the common standard for medical images, understood by equipment from every maker. One file holds the images (a single frame or a whole run of frames) and tags — data fields such as the patient’s name and date of birth, the date of the scan, the clinic, the machine and its settings.
The .dcm extension is not always there: on hospital discs the files often have no extension at all, next to a DICOMDIR index — it has its own guide. One study is usually tens or hundreds of files, one per slice.
What to open it with
- The program on the disc. Clinic discs often carry a viewer, but usually for Windows only and often out of date.
- Free desktop programs: Weasis (Windows, Mac, Linux), MicroDicom (Windows, free for personal use), Horos (Mac). They need to be downloaded and installed.
- A browser: OsonKit opens scans with nothing to install, on a computer and on a phone, and does not upload them.
How to view scans in your browser
Drop the files or the whole folder on OsonKit. The images are sorted into studies and series in slice order, and files that are not images, such as DICOMDIR, are skipped. Then pick a window (bone, lung, soft tissue), scroll through the frames, zoom, rotate and invert the image, and read the tags.
- Uncompressed images open, and so do RLE, JPEG, JPEG-LS, JPEG 2000 and HTJ2K. H.264 and HEVC video is shown frame by frame when your browser can decode it.
- One file up to 200 MB and 2,000 frames; a folder up to 5,000 files and 2 GB.
- The patient’s name, ID and date of birth stay hidden until you choose to show them.
Why not upload scans to a website
The tags of a scan carry your personal details, and many online viewers upload the files to their server first. OsonKit reads them right in your browser. You can check this yourself — this guide shows how.