Three-dimensional technology has reproduced a relatively faithful representation of physical reality in film and on television, and now it has the potential to do the same with breast cancer imaging.
Breast tomosynthesis - or 3-D mammography, in layman's terms - significantly improves breast cancer detection while simultaneously reducing recall rates over conventional 2-D mammography, according to supporters of the new technology.
But some experts warn that the benefits are not yet proven. Moreover, they say that tomosynthesis also exposes women to even more unnecessary radiation, since it's carried out on top of conventional mammography.
"Tomosynthesis hasn't yet replaced 2-D mammography, but it's very promising," says Dr Hung Wai-ka, honorary medical adviser to the Hong Kong Breast Cancer Foundation's Breast Health Centre.
Breast tomosynthesis was approved by the United States Food and Drug Administration in February 2011. It first appeared in Hong Kong later that year, at Tung Wah Group of Hospital's Well Women Clinics, according to the clinics' honorary consultant, Dr Lui Chun-ying.
Lui explains the technology behind 3-D mammography: an X-ray arm sweeps in a slight arc over the breast, taking multiple images in a matter of seconds. A computer then produces a 3-D image of the breasts in 1mm slices, providing greater visibility for radiologists to see tissue details. An exam using tomosynthesis takes about four seconds - similar to a conventional mammogram.
It was at the Well Woman Clinic, in Kowloon, that Hung, a specialist in general surgery, first used 3-D mammography. "Research data is still limited, but it's being used all over the world and experience will eventually accumulate," he says.
"In my opinion, it definitely helps improve cancer detection because it gives a clearer picture with a single mammogram. It has definitely boosted my confidence in screening and diagnosis."
Though tomosynthesis is being used as a screening tool in the US, in Hong Kong it is primarily used during patient recall for further evaluation of suspicious lesions that show up on 2-D mammograms.
At Hong Kong Sanatorium & Hospital, 3-D mammography has been used since February 2012, says Dr Gladys Lo, radiologist-in-charge at the hospital's Department of Diagnostic & Interventional Radiology. "[Tomosynthesis] is more beneficial for clarifying suspicious mass than a 2-D mammogram," she says.
Tomosynthesis could be used for a first screening - although it costs about double the price of a conventional mammogram - but Lui says the service is not being actively promoted.
Tomosynthesis may be better for certain women. "Young women with dense breasts or Asian women with smaller breasts may benefit from this new technique," says Dr Alex Ching, a radiologist at Matilda International Hospital, which only offers conventional mammography.
"There is some ongoing research on the potential benefits for those women with implants, different races, high-risk groups and patients with lumpectomy (partial removal of breast tissue)."
Ching adds that the 3-D machine is more comfortable for women because it requires less compression of the breast during the procedure.
Conventional mammography has played a significant role in women's health, reducing the mortality rate from breast cancer by as much as 50 per cent. But it has its limitations.
The fundamental flaw is that when the breast structure is compressed into a standard 2-D mammogram, overlapping tissue may hide lesions or cause benign areas to appear suspicious. This leads to call-backs of healthy patients, causing unnecessary anxiety and sometimes additional examinations such as ultrasounds.
According to the US National Cancer Institute, as many as 30 per cent of breast cancers are not detected by mammography and 8 per cent to 10 per cent of women who undergo mammogram screening are recalled for an additional check.
The overall recall rate of Tung Wah's screening programme is 8.8 per cent.
"Because of these limitations, 3-D mammography has the advantage of removing overlapping breast tissue so that we can see clearly where the lesion is," says Lui. "It also defines the lesion more accurately: whether it's a regular or irregular mass, smooth mass, or if there's radiating lines or distortion of the lesion."
The downside: the radiation dose from a 3-D mammogram is about 0.5 to 1.0 millisieverts - about 20 per cent more than a conventional mammogram. But it is still within the FDA's safe limits and relatively low in comparison to a CT scan of the head (about 2.0 millisieverts).
"[Tomosynthesis] is the first major advance in breast imaging and breast cancer screening since the development of breast MRI," says Dr Elizabeth Rafferty, director of breast imaging at Massachusetts General Hospital in Boston, the first to perform a clinical 3-D breast tomosynthesis exam in the US, in March 2011.
Rafferty has spent more than 10 years researching tomosynthesis. In one of her studies, published in the journal Radiology in November 2012, some 1,200 women underwent a standard digital mammogram followed by tomosynthesis, and the results were read by 27 radiologists.
Compared to digital mammography alone, the use of both standard mammogram and tomosynthesis resulted in increased diagnostic accuracy, and significantly decreased recall rates for further testing when no cancer was present (called a false positive result), for all the radiologists. In the Italian breast tomosynthesis screening trial, 7,300 women aged 48 years and older had both 2-D and 3-D mammograms. Radiologists then read the screens in two phases - 2-D only, then integrated with 3-D.
The combination of tomosynthesis and conventional mammography identified 8.1 cancers per 1,000 screens, compared with conventional mammography's 5.3 per 1,000 screens, an increase in the cancer detection rate of 53 per cent. The results were published in April this year in The Lancet Oncology.
Researchers at Yale Cancer Centre reported a 30 percentage point drop in recall rates - from 12 per cent to 8.4 per cent - among their patients using tomosynthesis versus conventional mammography. The study, published in the July 2013 issue of Radiology, involved more than 13,000 women, of whom 6,100 had tomosynthesis.
Most studies, however, have involved Western women. Asian women, in general, have relatively smaller and denser breasts, which may be an obstacle to detecting abnormal lesions. Studies done in Asia, however, have been small scale.
A study in this year's annual Asia Pacific Journal of Cancer Prevention by Japanese researchers found that among about 100 Japanese breast cancer patients, tomosynthesis was superior in diagnosing lesions in the form of mass, focal asymmetry or distortion, but not calcifications. In a similar study, Taiwanese researchers from Kaohsiung Veterans General Hospital, studying about 60 Taiwanese patients, had similar results - so, too, did radiologists at Tianjin Medical University Cancer Institute and Hospital, who assessed about 130 Chinese women.
At Singapore's Khoo Teck Puat Hospital, 50 women were screened using both 2-D and 3-D mammography.
The researchers concluded that tomosynthesis is "an important tool to reduce recall rates and to improve breast cancer detection, keeping patient [radiation] dose within safe limits" and that the findings support that the technology "can be used as [a] robust screening method in future".
Lui says Tung Wah is doing an observational study on its clinics' initial experience of using tomosynthesis. The goal is to confirm whether there are advantages for the Hong Kong population, its safety, and the response of the radiologists, surgeons and patients to the new technology.
For now, the technique should not be used outside of a clinical trial as it is not a "stand-alone" test yet and does not replace a regular mammogram, says Matilda's Ching.
"There is as yet no solid data to prove the 3-D technique finds more cancers or save more lives than traditional 2-D mammogram," Ching says.