Vendors tune products to stitch digital XR images together

Software advances promise routine future use

For digital radiography to succeed, its developers must demonstrate advantages that DR has over conventional film-based imaging. Speed in the acquisition and retrieval of images may not be enough. DR must open new clinical applications, just as new iterations of CT and MR have done in angiography and disease assessment. Image pasting, also known as image stitching or combination, promises to be one of those ice-breaking applications. Several vendors either have the necessary technology or they are developing it.

GE Medical Systems has product upgrades in the works for two digital radiography systems, the Revolution XQ/i and Revolution XR/d. The upgrades could be unveiled at the next RSNA meeting, and products could ship in early 2003, the company said. Agfa and Swissray already feature image pasting. Meanwhile, software developer AccuImage has devised a product that might be more generally applied.

Image pasting is designed to allow the visualization of long anatomies, such as the spine or legs. Conventional solutions involve the exposure of several film cassettes over the length of the anatomy. Once the images are obtained, they are pieced together to cover the area in much the same way pieces of a puzzle are assembled to form a complete picture.

Image pasting offers one-to-one image scale and the high detail inherent in screen-film technology. Conventional film-based methods, however, need special cassette holders or long film changers and special film processing equipment and incur the expense of longer film strips and higher doses of radiation. DR provides all the benefits with none of the disadvantages, according to Luc Katz, marketing manager for clinical research and advanced development, global x-ray, for GE Medical Systems in Buc, France.

"The purpose of image pasting is to get more clinical information," he said. "The digital solution visualizes long anatomies in a single image."

Digital options include computed radiography, which uses several cassettes to produce images that are read and pasted via a workstation, and DR, in which an x-ray tube and detector move in lockstep across the patient's anatomy. In both CR and DR, software electronically stitches the images to reconstruct the anatomy.

Agfa already offers this capability as part of its IMPAX for Orthopedics PACS product, released earlier this year (SCAN, 4/3/02). Exposures on as many as five phosphor plates are read by the company's CR system are stitched together using specialty software built into the orthopedics product.

DR systems from Swissray already feature image stitching, according to Rex Harmon, vice president of marketing. Software built into the company's SwissVision workstation combines up to five images. Harmon considers image pasting essential for orthopedics.

"It's extremely important for orthopedics, particularly those practices with more specialized aspects, such as scoliosis," he said. "That's the primary application of image combination."

Image pasting is also important to physicians interested in evaluating leg lengths and taking spot films of the hips, knees, and ankles, according to Harmon. This procedure is known as a scanogram.

When it comes to image stitching, DR outshines CR, according to Katz. DR inherently eliminates cassette handling, which is time-consuming and a source of error in both CR and film-based image stitching. The speed of DR minimizes artifacts due to patient movement. DR also offers good image quality, high resolution, and a large dynamic range with no geometric distortion.

The Revolution XQ/i and XR/d systems were developed with image stitching in mind. As a result, Katz said, building this capability into production units as well as upgrading the installed base should be relatively easy.

The XR/d is a table system, which can be configured with two detectors, one in an upright configuration. The XQ/i is a dedicated upright system. In each case, the standing patient would be scanned by the detector and x-ray source moving in unison from top to bottom.

Although obscure, this application could become routine, if the rest of the industry jumps on the bandwagon. The catalyst for that may be at hand. AccuImage of San Francisco has developed an image-stitching package called AccuStitch, and interest in the product has been growing. Leon Kaufman, Ph.D., CEO of Accuimage, said the product is ideal for DR. Several high-profile system manufacturers have shown interest in his product, Kaufman said, although he declined to name them.