How to open a .dcm file
DICOM medical image · Medical imaging
A .dcm file is a medical scan in DICOM format, the standard for MRI, CT and X-ray images. A free viewer such as MicroDicom on Windows or Horos on macOS opens it. Ordinary image viewers will not.
What a .dcm file actually is
DICOM is both an image format and a data standard. Alongside the pixels it carries patient identity, the machine that produced the scan, the acquisition settings and the study structure.
A single .dcm is usually one slice. A full study is a folder of hundreds of them, which is why a scan handed over on a disc looks like an unusable pile of files rather than one image.
Why it will not open
No operating system opens DICOM, and general image viewers do not implement it because the format is far more than a picture. Discs from hospitals often include a viewer that only runs on Windows, or refuses to run at all.
Renaming it to an extension you can open will not help: changing the extension does not convert the file, it only changes what Windows tries to open it with.
Step by step
Windows
- 01Install MicroDicom, which is free for personal use, and open the folder rather than a single file so the slices load as one study.
- 02If the scan came on a disc, look for a DICOMDIR file. That is the index of the whole study, and opening it loads everything in order.
- 03To convert a slice into a normal image, most viewers export to JPEG or PNG. Note that this discards the diagnostic depth of the original.
macOS
- 01Horos is a free viewer built for macOS and handles full studies.
- 02Preview will not open DICOM.
What usually goes wrong
These files identify a patient
DICOM embeds name, date of birth and identifiers directly in the file. Before sharing a scan with anyone, including on a forum for a second opinion, anonymise it. Most viewers have that function, and exporting to JPEG also drops the metadata.
A viewer is not a diagnosis
Being able to see the images is not the same as reading them. These pages help you open a file; interpreting a scan is a job for the clinician who ordered it.
Programs that open .dcm
Taken straight from publisher manifests. Some of these handle the format for a narrow purpose rather than as their main job.
Common questions
- How do I open a DICOM file for free?
- MicroDicom on Windows and Horos on macOS are both free and open full studies. Open the containing folder or the DICOMDIR index rather than a single .dcm, so all the slices load together.
- Can I convert a .dcm to JPEG?
- Yes, most DICOM viewers export to JPEG or PNG. Be aware you lose the full bit depth used for diagnosis, and that the export also strips the patient metadata, which is useful when sharing.