PARIS — Systems commercially available in Europe for a re-engineered mammography technology called tomosynthesis were presented by Siemens (Erlangen, Germany) and Hologic (Bedford, Massachusetts) during the French radiology congress held here this week.
These digitally-driven systems represent a strong response for X-ray based technology, which is the gold standard in the massive worldwide market for public screenings, and they assure a continuing role for X-rays against a growing competition with alternative imaging modalities.
Tomosynthesis technology is currently under clinical investigation in the U.S. and is not approved by the FDA.
Conventional mammograms produced by X-ray tend to raise more questions than answers for radiologists who routinely order biopsies of suspected anomalies with 80% of these tests returning a negative.
Other disadvantages of conventional X-ray include an uncomfortable procedure that requires compressing a woman's breasts, a radiation exposure that restricts the number and frequency of follow up exams, and long delays before results can be given.
MRI breast examination is especially valued by clinicians who have access to this modality where cancer is strongly suspected due to its precision, the reconstruction of multiple views and the quick turn around for reporting.
Advances in ultrasound technology include full volume reconstructions and the emerging potential of elastography for characterizing breast nodules as benign or malignant (Medical Device Daily, Oct. 20, 2009).
Ultrasound is the least expensive imaging technology, readily available, the least inconvenient examination procedure and provides nearly instant reports, creating a potential for replacing X-ray for screenings.
Facing this landscape, Hologic and Siemens reinvented their mammography capabilities by taking advantage of the emerging potential presented by digital radiology (DR) and the ability to design software to reconstruct acquired images.
The installed base of computed radiology (CR) using phosphorous plates is dominant with a steady but slow conversion to DR.
For the best DR is estimated by executives at the radiology congress to be 45% worldwide with a heavy skewing towards a more rapid adoption in the U.S.
A French executive said that among the 2,200 mammography units in that country, only 10% to 15% have been converted to DR.
The new tomosynthesis technology can be used to upgrade existing installation of the companies' DR mammography units.
In tomosynthesis, the projector tube moves through a programmed arc acquiring multiple images at low dosages of radiation while the detector plate under the compressed breast remains stationary.
The multiple images are reconstructed into 3-D images that allow the radiologist to scroll through layers of one millimeter to better visualize anomalies.
The effect is disruptive to conventional mammograms, presenting a video-like view of the compressed breast with an ability to reveal unexpected dimensions or complexity of an anomaly that appears only as a vague spot on a mammogram.
The multiple images acquired by both the Siemens Mammomat Inspiration and its competitor, the Selenia Dimension by Hologic, expose a patient to a radiation dosage equivalent to a conventional two-image 2-D mammography.
Siemens engineers decided on a wider angle of 50 degrees to scan the breast with 25 images acquired where the Hologic unit scans the breast in a 15 degree sweep acquiring 11 images for the reconstructed image.
According to Aurélie Riquet, Manager of Special Products with Siemens, a wider angle gives Mammomat Inspiration not only a greater number of slices for examination but a smaller pixel size that yields sharper images and enhanced contrast.
Riquet told Medical Device Daily, "We are waiting now for practice guidelines to say how this technology should be applied, and only the doctors can tell us this."
"Is tomosynthesis a screening tool?" she asks. "Is it best used for a secondary examination like MRI or elastography to confirm diagnoses? Today we cannot say and clinical practice will determine the answer."
Marc Urbain, Sales Director with Hologic in Belgium said, "We have done a great deal of pioneering work in tomosynthesis and decided upon a sharper angle for image acquisition."
"Clinical practice and studies will prove what is the better choice, narrow or wide angle," he added.
With the Selenia Dimension available since September 2008, Urbain said, "We have proved the market, winning customers at influential centers who are quite pleased with this enhanced technology and are amazed at what they are seeing in mammograhic exams as a result.
"At JFR we have three doctors presenting, two on digital breast mammography assessments using tomosynthesis and one on breast biopsy guidance using tomosynthesis," he said.
Andrea Van Steen, MD, from Catholic University Leuven (Belgium) presented at the French radiology congress his findings from a preliminary evaluation of tomosynthesis with 100 patients using the Siemens technology.
Van Steen reported a strong improvement of 26% in sensitivity and 22% for specificity in detecting anomalies over traditional mammograms and marked improvements in visualization of low-contrast structures, the contours of masses, and lesions, and a notably enhanced view of the structural distortions of lesions.
Carl El Khoury, MD, with the Medical Imaging group at the Institut Curie in Paris is conducting clinical studies with a Siemens Mammomat Inspiration.
"Published studies on tomosynthesis, regardless of the system used, show there is a better visualization of opaque tissues on reconstructed slices compared to standard mammography," he said.
"Currently, looking at mammograms that are sufficiently ambiguous we ask for a more targeted image, often an MRI scan. Is tomosynthesis going to take up this role where the MRI currently is indicated?" he asks.
"Can a secondary examination of ultrasound elastography combined with tomosynthesis deliver a superior initial examination than with current practices? We are still in a period of exploring this possibility," he said.
Hologic's Urbain reports the company has a total of 20 units installed and operating in the Netherlands, Germany, France and the UK.
"We are exceeding our sales targets to this point with early adopters of the technology and have an extremely high interest with many clinicians waiting for further studies to show that tomosynthesis brings something new and better to their examinations," he said.
Siemens installed pre-release Mammomat Inspiration units with tomosynthesis at reference hospitals in Germany and Belgium, according to Riquet.
"Customer visits to these sites have resulted in enough orders that there is a little waiting list at the moment," she said.