DICOM committee to add display QC ability

November 1, 1998

DICOM committee to add display QC abilityOne of the often-cited benefits of soft-copy reading is that radiologists can easily manipulate the images to assist in making the diagnosis. Unfortunately, this capability can turn into a disadvantage

DICOM committee to add display QC ability

One of the often-cited benefits of soft-copy reading is that radiologists can easily manipulate the images to assist in making the diagnosis. Unfortunately, this capability can turn into a disadvantage when the images are viewed at a later date. If images are viewed by somebody else on a workstation with different characteristics, it may not be possible to recreate exactly the same display conditions.

To address this problem, the DICOM committee has specified a new DICOM service, called "soft-copy presentation state," which enables workstations to determine what viewing operations, such as windowing and leveling, were employed during the diagnosis.

A workstation that supports this new service memorizes how the image was initially viewed, stores this in a presentation state object, and sends the information along with the image to other devices that support the interpretation of this new DICOM object. The receiving device interprets the presentation state and knows exactly how to recreate the initial image appearance. Multiple presentation states can also be supported.

The soft-copy presentation state addition would not have been possible without the recently approved DICOM gray-scale function display standard, which defines how soft-copy displays (as well as hard-copy devices) can present images in a consistent manner.

Most of the video display boards that are used for diagnostic displays already provide calibration tools to adjust the imaging board and monitor to comply with the new gray-scale display function standard. This is typically a light (luminance) meter, which is placed on the monitor surface while a software test program varies the input values to measure the whole range of the display. A calibration or correction curve is generated and stored on the video board so that the deviation from the display standard can be automatically incorporated before displaying the image.

The soft-copy presentation state proposal is currently "frozen," which means that it is available for early implementations. In addition, the DICOM committee is supporting a demonstration at the next European Congress of Radiology, to be held in Vienna in March. A consortium of several universities and vendors will develop the demonstration, which will be made available in the public domain after the conference.

This addition to the standard will be a major step toward image consistency and integrity for sof-copy display. It represents how DICOM is expanding beyond communication of images. As with all new DICOM supplements, the proposals are available from the NEMA server at ftp.nema.org.

-Herman Oosterwijk, president, OTech Inc. (herman@otechimg.com)