TIn the United States, studies have been underway for several years investigating the benefits of digital mammography over conventional mammography methods, and consumer demand for the advanced modality is on the rise. Such phenomena are hardly unique to the United States. Full-field digital mammography is generating interest as an alternative to conventional film-based imaging abroad as well, where the benefits of radiation-dose reduction, improved images, and computer-aided detection (CAD) are exciting radiology departments and consumers alike.

The radiology department of the University Hospitals of Leuven, Belgium, is one facility embracing the advances of digital imaging. In fact, with the exception of mammography, the radiology department is already completely digital, and according to the head of the radiology department, the physicians like the direction in which they are headed.

"Our radiologists definitely do not fancy returning to a film-based situation," according to Professor G. Marchal, Phd, MD. "They feel that the system has made them more productive while at the same time able to deliver better quality."¹ Whether that will be the case with mammography remains to be seen, as Leuven has only started evaluating systems for digital imaging in the past few years. Leuven began doing clinical testing and evaluating a new computed radiography (CR) system by Agfa-Gevaert in 2001, and installed Agfa's digital radiography (DR) system in the breast center this year. Chantal Van Ongeval, MD, specializes in breast imaging and biopsy techniques at the center. She says, "Digital imaging is now present in many hospitals in Belgium, and mammography is the last modality to be converted. We are still following conventional methods, so digitizing this unit is very important."

THE BREAST CENTER

The University Hospitals in Leuven are the largest hospital complex in Belgium, with five sites in different locations under centralized management. In the radiology department, which has a staff of 22 full-time radiologists and 40 residents, some 450,000 radiological examinations are performed each year. The radiology department produces around eight terabytes per year of raw data, and images are kept online indefinitely, accessible through the centralized information system that Leuven installed 15 years ago. There are 30 diagnostic viewing stations in the central radiology department.²

The Leuven radiology department is now almost entirely filmless, but radiologists still perform conventional mammography examinations within the breast center. The center is part of the department and features three mammography systems for conventional imaging, two ultrasound machines, and one stereotactic table. The breast center has three full-time staff members, and radiology students from University Hospitals rotate through the department as well.

According to Van Ongeval, Belgium advises women between the ages of 50 and 69 to get a mammogram every 2 years. The Belgian system also has been putting an increased emphasis on screening credentials, and Marchal says that Leuven's radiologists have completed the proper examinations in order for the facility to be accredited. The facility is also involved in a governmentorganized screening project that involves reading mammograms from its own center and from 85 other centers and a mobile unit.

"Our mammography department has been one of the fastest-growing areas in the hospital over the past 5 years due to an increase in screening mammography," Marchal says. Van Ongeval says that the center performs about 6,000 ultrasound examinations and 1,000 minimally invasive techniques (such as core biopsies, fine-needle aspiration cytology, and vacuum-assisted biopsies) each year. Marchal notes that, in addition to about 22,000 mammograms per year performed in the department, "Radiologists are responsible for the first and second reading of the mammograms coming from the mobile unit and from the radiology centers in the neighborhood of Leuven. In total, we read about 42,000 screening mammograms each year." Leuven's radiologists read screening mammograms using guidelines set according to key performance indicators from the European Guidelines for Quality Assurance in Mammography Screening.³

TESTING THE DIGITAL APPROACH

With the sheer volume of mammograms being read in the department, making a transition to digital imaging only made sense, according to Marchal. "There was interest in going digital because the radiology department needed fast throughput for screening mammography with high resolution," he says. The modality also had the appeal of giving radiologists the ability to fine-tune images (for example, by changing transparency to view soft tissue or zooming in on a possible microcalcification zone); to review images in real time; and to solve image storage and transmittal problems.⁴ The radiology department, therefore, has been testing the CR and DR systems in several capacities, both technically and clinically, according to Van Ongeval. Because the European guidelines for quality control of digital images are not finished yet, however, the digital technology cannot be used for screening purposes. Both systems are connected to the department's picture archiving and communications system (PACS) and optimized for screening, but the radiologists are continuing to do side-by-side comparisons with analog images until they can resolve quality-assurance issues and assess work-flow differences.

Chantal Van Ongeval, MD, specializes in breast imaging and biopsy.

"Because the two different systems are in the test phase, no important changes have yet been made in the reading room," Van Ongeval says. The radiologists at Leuven currently perform both hard-copy and softcopy readings, and conventional imaging is part of the clinical testing. "Depending on the results of the testing, further decisions about clinical use will be made," Van Ongeval adds. "To date, the greatest benefit is that images can't get lost. New printing of the images stored on PACS is always possible. In comparison with previous examinations, the scans also are quickly read. Although image quality is always the first issue, in the end, the price of the system will make the difference."

Radiologists need to address several key issues, including quality assurance, which has so far posed the biggest challenge with the new technology. Van Ongeval also stresses that considerable investigation is still necessary into the postprocessing of the images, the differences between hard-copy and softcopy reading, the need for CAD, implementation in mobile units, and the evaluation of images coming from different systems on one PACS monitor in one center. "To date, we have not found the optimal processing for the digital images," she says. "How to provide quality control for our digital equipment is an unsolved problem. To optimize the processing of a digital image is more difficult than for analog," Marchal adds.

A thorough systems analysis is an important prerequisite to purchasing digital mammography equipment, of course, but according to Professor Hilde Bosmans, MRI engineer and head of the physicists of the screening mammography program, comprehensive evaluation of the three key parameters of spatial resolution, image contrast, and noise is potentially very time consuming. That makes the management of quality in digital mammography a challenge.¹ Bosmans points out, in particular, that the risk of uncertainties and the variations in detectors make it essential to perform spatial- resolution measurements all over the image. Finding a workable method of collating these data and ensuring that localized problems are detected is, therefore, an ongoing problem. In addition, phantoms used for image contrast measurement should mimic clinical scenarios as closely as possible, projecting irregular shapes rather than a grid of uniform holes. Leuven researchers have been testing a contrast detail phantom in which very small pieces of eggshell are used to simulate microcalcifications. Use of an authentic-looking anatomical background also helps make the test conditions as realistic as possible, according to Bosmans.¹

In spite of the remaining hurdles, the radiologists at Leuvens have hope for this new technology's potential to improve their dayto- day work. "Our goal is to see more patients, especially for screening, and our constraints are less related to the equipment and the issue of digital versus nondigital systems than they are to the ability to read the images quickly. If we can do that, it will leave our radiologists free to read more films, talk with patients, and so on," Marchal says.

"Digital technology's added benefits will include work-flow improvement (thanks to our ability to see previous images online, which will improve diagnosis)," he continues. "The immediate availability of the image means quicker turnaround for the technologist, and CAD will bring additional advantages. Overall, it's the quality of care that is improved by going to digital, as well as the overall operation of the department. This technology can help us see increased numbers of patients and return a more accurate diagnosis to them."

Elizabeth Finch is a contributing writer for Decisions in Imaging Economics.

References:

1. Gould P. Quality doubts persist in digital mammography: automated evaluation avoids lengthy system analyses. Available at: www.diagnosticimaging.com. Accessed September 24, 2003.
2. University Hospitals in Leuven put clinical user at center of process in optimization of inter-departmental workflow. Available at: www.agfa.com. Accessed September 24, 2003.
3. European guidelines for quality assurance in mammography screening. Available at: www.tumorzentrum-aachen.de. Accessed September 24, 2003.
4. Digital radiology solutions for mammography. Available at: www.agfa.com. Accessed September 24, 2003.