I have two applications on my Mac that will open DICOM files: OsiriX and Horos.

In response to a download and display request in Safari, I get the message shown in this screenshot:

The request is: osirix://?methodName=DownloadURL&Display=YES&URL='http://207.254.60.XXX:3333/wado?requestType=WADO&studyUID=1.2.826.0.1.3680043.9.5830.1.XXX&token=5EA4A2D69BC4AA5BB4A2CD303B7FE041'

(XXXs for anonymization purposes)

It previously would simply download the data into Osirix and display them. Now, suddenly, I get the option to open the data with Horos only.

This doesn't happen with Chrome.

Update 12/22/16: It's happening with Chrome, too. Chrome opens the Horos app.

Second update: 12/22/16

Firefox Preferences still permits explicit specification of Applications. When I checked this, I got the following:


I changed this to "OsiriX" which has solved the issue for that browser. So, I've confirmed that "something" has set Horos.app as a Default. I just have to determine how to change that.


2 Answers 2


Have you tried downloading a DICOM file locally and then right clicking -> open with -> Other and then choosing Osirix and checking always use this app? I've had to do this before once; somehow OS X file associations got overwritten after an upgrade.


I used RCDefault.app to fix this. Yes, Horos was listed as the URL Handler for OsiriX. I don't know how this came to be.

I confirm that RCDefault does work in macOSSierra (10.12.2) — at least for this purpose. (I read somewhere that it wasn't working in Sierra.)

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