DICOM image files contain header information and image data. Patient information is stored in the header part of the file, and may also be embedded in the image or pixel data. There are several anonymization tools that are part of the RadPix teaching file system.
As the DICOM images are first received, each passes through a series of pipelines, evaluating each file for the presence of patient information.
DICOM Header Anonymizer
DICOM Supplement 142 describes the DICOM fields that must be removed or modified in order to ensure anonymization. The default configuration of RadPix teaching file system adheres to these rules. The anonymizer can be modified for specific other tasks, such as retaining some patient information. This is best explained in a use case:
A radiologist sends some images to the RadPix teaching file system for later use while reading cases. Later, he /she logs onto the server to view the images. The case with the images are initially in the Draft mode. In order to help the user remember the case, the patient name and /or number can be retained and viewed. When the case is edited and subsequently saved, the patient name and / or number can be automatically removed by the server.
The DICOM Header Anonymizer script can be edited by the administrator by clicking on the gear tool icon.
DICOM Pixel Anonymizer
Some DICOM images have patient information embedded in the image / pixel data. For a given device creating these types of images, there is typically a defined region on the image where the patient information is stored. Based on a combination of DICOM element values, these specific images can be identified, and specific regions of the image can be “blacked out”. While this feature is useful, it is not perfect. It is up to the institution where RadPix images for the teaching file software is installed to monitor the images for the presence of patient information embedded in images. There is a scripting language available to support additional image types. The DICOM Pixel Anonymizer script can be edited by the administrator. Contact firstname.lastname@example.org for assistance.
DICOM Image Filter
Some images have patient information in unpredictable locations. For instance, paper documents scanned into the PACS may have handwritten notes on them, including patient information. These types of files can be filtered or discarded as they are processed by the RadPix teaching file system. This function is also done by evaluating DICOM elements for specific values.
The DICOM Image Filter script can be edited by the administrator by clicking on the gear tool icon.
There are some DICOM images that the system does not recognize, and these images may be placed into a “quarantine”, meaning they are only visible via the quarantine link for system administrators.
Black Out Tool
Despite the above steps aimed at anonymization, there are still some images that contain patient information in the image data. When the case is edited, a special “Blackout” tool can be used to draw a rectangle on an image, and when saved, the DICOM image is modified by blacking out the part of the image defined by the rectangle. The tool also shows the coordinates of the rectangle, which can also be used to more easily add rules for the DICOM pixel anonymizer.