Is Digital the Answer for Mammography?

3 June 2010 (Last Updated June 3rd, 2010 18:30)

Digital mammography has many benefits, but will its cost and false positives open the doors for new technology? Libby Harkness investigates.

Is Digital the Answer for Mammography?

The Breast Cancer Institute (BCI) joined forces with Australian retail giant Myer last year to open digital mammography clinics in the lingerie departments of four of Myer's Sydney department stores: at the same time as doing her shopping a woman can now book a free mammogram.

The clinics, which have a bright sunflower theme, are part of the BCI's programme to raise awareness about breast health in traditionally low-screening areas. The mammogram takes just a few minutes and within two hours the scan is at the hospital, where it is read by two doctors.

At the clinics being set up in selected hospitals, BCI is expecting to screen about 200 women a week, of which one cancer diagnosis will be made. This example highlights just how far digital mammography technology has come and the benefits it offers beyond traditional film-screen techniques. But while digital provides many opportunities, it comes at a cost that some providers may look to put off as newer technologies come to the fore.

Film-to-digital transition

"At selected hospitals, BCI is expecting to screen about 200 women a week, of which one cancer diagnosis will be made."

Film-screen mammography for breast cancer detection has been used for over 50 years and today it remains the primary method for general screening. No other method has been subject to the rigorous evaluation of mammography that film screening has, and it is still the only method for which the reduction in breast cancer mortality has been shown in randomised trials.

Newer digital mammography technologies have been commercially available for years, but the uptake has been slow despite its advantages over film, however, this is starting to change. According to the US Food and Drug Administration (FDA), more than 50% of mammography units in the US today are digital.

Part of the reason for this growth is that digital mammography provides better soft tissue contrast than film techniques and better x-ray penetration of dense breasts. This makes it more accurate for use on younger women, whose breast tissue tends to be much tighter.

Digital imaging is also recognised as providing a more consistent image quality and has a diagnostic accuracy that is at least equivalent to film. This improved image quality helps with better identification of calcium and because the images can be manipulated on the computer screen, areas of interest can be viewed in more detail without the need for extra mammographic views. Techniques with digital mammography are also considered to be much cleaner (no chemicals are used and there is a reduced exposure to radiation).

But according to Professor John Boyages, executive director of the Westmead Breast Cancer Institute (BCI) in Sydney, Australia, one of the real advantages to digital mammography is the instant feedback.

"We have reduced our screening time from about 15 minutes to between five and seven minutes," says Boyages.

For medical facilities, digital mammography techniques have also been worth the cost for their reduction in architectural footprint. A whole work area can be contained in one small room, making it suitable for mobile unit screening, use in rural areas, and in situations like the department store case study mentioned above. Using the internet, images at a screening site can be easily transmitted to another site for evaluation.

Where digital costs

Digital, however, has its drawbacks, one of the biggest being its cost. Digital equipment can be three to four times more expensive than traditional film screen.

"We have reduced our screening time from about 15 minutes to between five and seven minutes."

In terms of capital expenditure for the private sector, it has been prohibitive because of the difficulty in getting an economic return. The capital costs are more efficient with mass screening programmes when the cost of film, time, space and less radiation exposure are factored in.

Another disadvantage is the potential for computer storage problems created by the large number of files from mass screening. The cancer detection rate may increase, but the recall rate from false-positives can also be high. Like any new technology, this is a bug technologists say will one day be ironed out, but for a hospital today this still equates to cost.

New mammogram technologies on the rise

Research programmes are focusing on how to overcome the issues with film and digital mammogram techniques. The market is there for those who find a solution, especially as a number of countries now offer free (or low cost) mass screening programmes for breast cancer.

While at times controversial, breast screening has been widely used long enough to statistically measure benefits. Denmark, which does not have a breast screen programme, has the highest breast cancer mortality rate at 27.8%. Compare this with countries such as the UK (24.3%), US (19%), Australia (18.4%) and Sweden (17.3%) and the advantages of screening are clear.

One debate that has risen in all countries carrying out screening focuses on age. While 90% of breast cancers are found in women over the age of 50 there has been conflicting evidence about the screening benefits for younger women. Today's screening techniques find it difficult to predict cancer in this age group because of breast tissue density issues, so it is unknown if figures for women under 40 years, for example, are an accurate measure.

Another area for consideration when beginning regular screening on younger women, however, is exposure to radiation over time and the impact this can have. Improvements in techniques and diagnosis are making it possible to detect increasingly smaller lesions but the use of new and multiple methods of diagnosis is providing new challenges. For example, digital mammography, does not provide tomographic information and may not detect tumours masked by some normal anatomical features; digital breast tomosynthesis (DBT) has evolved as a way of addressing this problem. DBT produces mammogram-like images at different depths.

Recent technological advances have also seen the scope of ultrasound in breast imaging increase. With no radiation and widespread availability, it is easy to see why this technology is attracting attention. The downside, however, is that it is easy for users to make errors, which can often lead to false positives.

"Hope now rests on emerging imaging technologies for early breast cancer detection."

Breast elastography, a technique to determine the shape and firmness of body tissue, can also aid diagnosis where ultrasound-based imaging is used and the use of magnetic resonance imaging (MRI) has increased in recent years, particularly as a supplementary procedure for further assessment following mammograms or ultrasound.

The American Cancer Society (ACS) and the European Society of Breast Imaging (ESBI) recommend MRI as an adjunct to mammography for women with a 20% or greater lifetime risk of breast cancer.

The disadvantage of MRI is that it is expensive to use and has an increased number of false positives.

Early detection hope

Hope now rests on emerging imaging technologies for early breast cancer detection - MR / optical hybrid imaging, breast-specific gamma imaging (BSGI), positron emission mammography (PEM) and contrast injection mammography where tumours may only take up a small amount of the intravenously injected x-ray agents. It is now hoped that these technologies will achieve what may have seemed to be technologically and financially impossible a few years ago.

"New techniques are being invented [but] right now mammography remains the best we have for early diagnosis," says Boyages. "In a hundred years' time we may look back and say 'how archaic – must have been invented by a man'."