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Mammography has always been held to a higher level of diagnostic quality than garden variety imaging devices. So when full-field digital mammography came to market, the entire system-from the detector to the acquisition workstation and display
Mammography has always been held to a higher level of diagnostic quality than garden variety imaging devices. So when full-field digital mammography came to market, the entire system-from the detector to the acquisition workstation and display monitor-had to be validated by clinical data as part of the FDA's premarket approval process (PMA). Now, years after the first FFDM entered the U.S. marketplace, the FDA has clarified the situation by explaining how PACS workstations cleared through the 510(k) process can be used to review mammography images.
Displays that present these images in a PACS environment do not require PMAs, because images transferred from a digital mammography system to a PACS display station are generally not changed, according to the agency. Rather, they are in final image form and transmitted using the DICOM standard. Those viewing the images are able to perform image manipulation such as contrast, gray-scale, or edge enhancement, which have traditionally been functions of PACS viewing stations. Such stations therefore need have only 510(k) clearance, according to Dr. Robert Phillips, chief of the Radiological Device Branch, Office of Device Evaluation, in the FDA's Center for Devices and Radiological Health in Bethesda, MD.
But there is a limit to the good news. Monitors used within PACS must be cleared for mammography image display if the PACS station is intended for use with mammography images. This means they must be capable of expressing sufficient diagnostic detail. The PACS and the display, therefore, must at a minimum be able to capture 5-megapixel full-breast images and have other technical characteristics specific to individual types of display technology, such as those associated with CRTs or flat-panel systems, said Dr. Kish Chakrabarti, an expert review scientist with the FDA.
Under these rules, Agfa received a 510(k) clearance for its multimodality dedicated and scalable mammography diagnostic workstation, which leverages its IMPAX PACS networking environment for soft-copy review. The 5-megapixel unit, developed in conjunction with Barco, has 2048 x 2560-pixel resolution.
U.S. Electronics received 510(k) clearance for the ME511L flat-panel LCD for diagnostic reading of mammography images in a PACS application. The ME511L, which is manufactured by Totoku, displays 5-megapixel monochrome images on a 21.3-inch diagonally measured screen.
Companies with full-field digital mammography systems are permitted to use an imaging station that has already been cleared under the 510(k) process, as long as the display meets minimum technical specifications and all image construction activities are performed prior to the image being sent to the display station, Phillips said. When some of the image construction is performed in the FFDM display station, PACS devices can be used, as long as the FFDM display station outputs a finished image in a compatible format such as DICOM.
The FDA departs from this stance with newly developed acquisition workstations. Because these devices house the intelligence of a mammography system in terms of capturing the signal from a digital receiver and producing an image by means of proprietary algorithms, they are considered to be part of the PMA product and must go through the PMA process, Phillips said.
The complexity created by using both PMA and 510(k) processes to review digital mammography displays is causing considerable confusion among manufacturers and buyers.
"There are so many different levels and approaches with the FDA clearance, it's hard to keep track of everything that's gone on in the market," said David Hebert, marketing manager with the medical business unit at Planar Systems.
The imaging community will get a chance to catch up at the RSNA meeting, where the FDA plans to have two educational sessions on the subject to clarify its position on approval of mammography displays. In the meantime, the makers of monitors are feeling their way.
Planar recently had to meet a higher threshold of evidence to obtain 510(k) approval of its Dome C5i diagnostic quality active matrix LCD as a stand-alone display. The Cs5i already had 510(k) approval from the FDA for viewing images in a PACS application. Isaac Fram, senior product manager for new products in Planar's medical business unit, explained that the product submission for the stand-alone C5i included clinical data acquired in scanning mammography, as well as technical equipment information associated with processing and displaying data. The clinical data, obtained in a trial at the Elizabeth Wende Breast Clinic in Rochester, NY, included blinded image analysis by six independent radiologists of microcalcifications and architectural distortions on CRT displays as well as the C5i LCD panel, as measured on a nine-point Likert scale. The objective was to show that LCDs were at least as sensitive as CRTs.
Increased regulation and the effort to meet higher standards typically translate into higher costs for the consumer, because more advanced technology needs to be developed. The higher standards set by the FDA for stand-alone mammography displays and new acquisition workstations, however, might not have that effect, according to Hebert. Planar, for example, has applied existing technology that inherently meets the higher standards. And that can make all the difference.
"This way we can achieve FDA clearance at the level required for mammography and do it at price points consistent with PACS displays," he said.