DICOM Update: InfoRAD demo to highlight image consistency

November 1, 1999

InfoRAD demo to highlight image consistencyBy Herman Oosterwijk, president, OTech Inc.Walking from booth to booth at the annual RSNA meeting in Chicago provides an overview of many different workstations from

InfoRAD demo to highlight image consistencyBy Herman Oosterwijk, president, OTech Inc.

Walking from booth to booth at the annual RSNA meeting in Chicago provides an overview of many different workstations from a variety of vendors. The problem is that it is hard to make comparisons among those products. At one particular booth, a digitized chest x-ray might look great. You try to keep that picture in mind as you walk several hundred yards to another vendor’s booth, only to see a completely different image on the workstation there. In addition, the lighting is not the same, the lookup tables used to correct the image prior to displaying it are not identical, and a different mapping of pixel values onto the monitor may have been employed. The bottom line is that comparisons of the two workstations are extremely difficult.

Vendors obviously like to differentiate their products from others; however, the DICOM committee’s goal is standardization. Its objective is that the digitized images look as close as possible to the way they appeared on the original film, reprinted film, or diagnostic viewing station. How can this be ensured? And what if a radiologist zooms an image, changes the window width and level, and adds an annotation and text to the image before sending it to a remote site? How can the zoom, overlay, annotation, and window level/width information be preserved so that every physician looking at that image sees the same presentation?

All these issues can be addressed with two new areas of the DICOM standard: gray-scale consistency and image presentation state. For consistent gray-scale, the DICOM working group originally defined the so-called gray-scale standard display function (GSDF) curve, according to which monitors and printers are calibrated.

A new soft-copy presentation state service has also been specified to handle image appearance and manipulation, including zooming, specific window level and width value, overlay displays, masks and/or shutters, and preservation of image orientation.

The NEMA Committee for the Advancement of DICOM and the RSNA will host a demonstration of these two new DICOM services in the infoRAD exhibit (booth 9724) at the upcoming RSNA meeting. A network of workstations from different vendors will be installed with software that creates, renders, and stores presentation states, applies presentation states to images, and prints images as rendered by a presentation state on different printers. All monitors will use the same image source and lookup tables and will be calibrated to the same GSDF curve.

This demonstration is designed to allow users to compare different viewing technologies from various manufacturers and to determine the feasibility of the DICOM soft-copy and hard-copy presentation standard.