DICOM viewer privacy: why offline beats uploading your scan

An offline DICOM viewer reads your scan on your own device and sends nothing out. A viewer that uploads copies your files to a server first. For personal medical images, keeping the file on your device is the simpler and safer default.

This is not a reason to worry. It is a question of how many copies of your data exist and who holds them.

What is inside a DICOM file

A DICOM file is more than a picture. Besides the pixels, it carries a block of fields, called tags, that describe the patient, the study and the equipment. These commonly include the patient’s name, birth date and ID, the date of the exam, the hospital or clinic, and the device used. See DICOM tags and metadata.

Those details are stored inside the file. Renaming the file to something neutral does not remove them. Opening a study means handling both the images and the identifying information in the same package.

How uploading viewers work

Some viewers, especially in a browser, work by sending the files to a server. The server processes the images and sends back what you see. This can be convenient, because nothing needs to be installed and heavy work happens elsewhere.

The tradeoff is that your files now exist somewhere else. Questions that follow:

• How long is the copy kept, and who can access it?
• Where is the server located?
• Are the files stored in a form that includes the patient fields?
• What happens if you want the copy deleted?

Good services answer these in their policies. You still have to read them, and you have to trust the answers. With an offline viewer the question does not arise, because no copy is made.

What offline means in practice

Viewing a scan does not need a server. A phone can decode and draw the images itself. An offline viewer:

• reads the file you choose from local storage
• decodes and displays it on the device
• keeps working with the network switched off

You can test this yourself. Turn on airplane mode, then open a study. If it loads and scrolls normally, the app is not relying on a connection to show your images.

Questions to ask of any viewer app

1. Does it upload your files, or their names? File names can contain patient names too.
2. Does it need an account? An account links your use of the app to an identity.
3. What does the data safety section say? On Google Play it lists what an app collects and shares. Compare it with the privacy policy.
4. What permissions does it ask for? A viewer has no need for contacts, location or microphone.
5. What does it measure? Many apps send usage counts. The point to check is whether any of it can contain file names or image content.

If you cannot find clear answers, treat that as information too.

What one offline viewer does

These are the facts from the app’s own description and policy.

• Radix DICOM works fully offline. Opening and viewing do not need a connection.
• It has no account and no ads.
• It never uploads your images or file names.
• It sends only anonymous usage counts. The full list is in the privacy policy.

It is Android only for now. It is a viewer, not a medical device, and it is not meant for diagnosis. Decisions about your care belong to your doctor.

When uploading is the right choice

Offline is not always the answer. If a clinic asks you to send a study through its own portal, or a specialist needs to see the images remotely, then sending the files is the point. In that case the clinic chooses the channel, and you follow its instructions. See how to share a DICOM scan for a second opinion.

The difference is who decides. Using a viewer on your own device means your scan stays with you until you choose to send it to a specific person. Using an uploading viewer means a copy is created every time you simply want to look.

Getting a scan onto your phone

Most people receive a scan as a disc, a download link or a zip. A phone cannot read a disc itself, so copy the folder to a computer first and then transfer it to the phone. See open a DICOM CD on your phone. Whichever route you use, keep the folder together, and delete the temporary copies you no longer need.

A habit worth keeping

Before you open a scan in a new app, spend a minute on the checks above. Look at the permissions, read the data safety entry and try airplane mode. It costs very little, and it tells you whether the images stay on your device.