Future Directions in Breast Imaging
(updated September 2011)
 

Digital Mammography 

X-ray film mammography (conventional mammography) until today remains the single best screening method for early detection of breast cancer. However, new developments in digital mammography have shown that digital mammography can be as good as film mammography in screening. More than 49,000 women underwent both digital and film mammography in the United States and Canada. The results as reported in the New England Journal of Medicine, 2005 showed that the diagnostic accuracy of both digital and film mammography was similar and that diagnostic accuracy of digital mammography was slightly better for women younger than 50 years, women with heterogenous or extremely dense breasts and women who were pre or perimenopausal.

A digital mammography unit looks like a conventional mammography unit and both use x-rays to image the breast. However, in a digital system, a special detector (eg selenium) instead of a piece of film picks up x-rays leaving the breast. This detector converts these x-ray photons into light and the light is converted into a digitised signal that is displayed on a computer monitor. This technology may be better at visualising tumours in dense breast tissue, a current limiting factor in conventional film mammography. In addition, one can change the contrast of the image, instantly compare it with others in the archive and share the image across the telephone line with experts in main centres. A simple analogy would be comparing film cameras with digital cameras!

Unfortunately the cost of full field digital systems is high and is about 4 times the cost of the best conventional film mammography system. The maintenance costs are also higher than conventional mammography systems.

Advances in ultrasound technologies

Ultrasound has proven its credibility as an adjunct to mammography since the late 1970s. The advantages of ultrasound include being relatively less expensive than other modalities, not requiring radiation and being relatively more widely available.

Ultrasound scanners for imaging the breast needs a high frequency transducer (probes) of at least 7.5 MHz and higher. Its forte is in providing a better view through dense breast tissue than conventional mammography. Ultrasound applications for breast imaging include aspirating cysts, distinguishing solid from cystic lesions and guiding biopsies.

Unfortunately, ultrasound is very much dependent on the skill of the operator (the sonographer or radiologist) and until there is a method to make it more mechanical and reproducible, it is not ready for large scale screening in a systematic fashion. Although there is a routine that must be undertaken by all operators, there will be some who have better visual skills at picking up abnormalities. The operator also needs to be motivated and interested in breast imaging. Naturally, those who are properly trained and perform breast ultrasounds regularly will be better at picking up abnormalities.

A high frequency transducer (probe) is essential for breast imaging.  Breast-specific scan heads maximises ultrasound’s potential. Real Time Compound Imaging uses computed beam steering technology to steer the ultrasound beam right to left to create an image composed of nine lines of sight rather than a single one. The images produced more closely resembles computed tomography (CT) or magnetic resonance imaging (MRI) images. Clinical trials of compound imaging technology have been encouraging and improved visualisation of breast lesions has been reported.

3-D ultrasound using the free hand (hand held) transducer has not proven to be very useful in characterisation of breast masses on ultrasound. Instead, today, Automated Whole Breast Ultrasound (ABVS) is beginning to gain a foot hold in many centres in Japan, USA and Germany. What the ABVS can do is to provide standardised volume views of the breast and therefore remove user dependency. In addition the information density is improved since within a standard time for acquisition by the radiographer/sonographer, the volume data is of or nearly of the whole breast. In addition, reproducibility is improved for second opinions and discussions, without needing to recall the patient. This has proven useful in clinical settings for detection of additional lesions after the primary/ index breast cancer has been found. It changes the management of patient when the breast cancer is multiple rather than single.

With newer, more expensive and better ultrasound machines, clinical trials will investigate if ultrasound can indeed be promoted for breast screening in the future.
 

Magnetic Resonance Imaging (MRI) of the breast

Research into breast MRI began in the 1980s. MRI has been shown to identify cancers not present on mammography or ultrasound. Ever since contrast enhancement came on the scene, interest in MRI has intensified. As breast tumours have their own blood supply when they reach a certain size, contrast medium (gadolinium) “lights up” the blood supply to the tumour when imaged by MRI. 

Its use has been limited until now as a diagnostic test and for staging cancer after it has been detected on a mammogram. It is also useful in the detection of recurrence after surgery has been done for removing breast cancer. Unlike mammography, it does not detect calcifications but images blood flow to determine shape and size of the tumour. 

In the next few years, more studies will be performed to establish more clearly the clinical performance and role of MR imaging in the detection and diagnosis of breast cancer. This will include studies of the accuracy of breast MR imaging in the evaluation of suspicious breast lesions detected at mammography or clinical examination, the accuracy of breast MR imaging in the evaluation of the local extent of breast cancer, and the potential role of breast MR screening of high-risk populations.

Already, it has been established that there is a small percentage of breast cancers which are only seen on MRI. The drawback of large scale MRI use is the need for dedicated biopsy units, high cost and low availability as well as low specificity (it picks up too many lesions, most of which are not cancer but have to be evaluated as the nature is unknown).
 

Nuclear Medicine breast imaging techniques

Nuclear medicine breast imaging techniques with use of single-gamma (scintimammography) or dual-gamma (positron-emitting, PET) radiotracers are being considered as complementary modalities to conventional mammography for breast cancer diagnosis and characterisation, for evaluation of metastases, and as an aid in the selection of appropriate therapies.

Nuclear medicine imaging is a way of obtaining functional or metabolic information that could potentially decrease the number of unnecessary biopsies performed and may also act as an adjunct imaging modality for patients with radiodense breasts. 

With future developments, it will most likely be of clinical value in cases where conventional imaging gives indeterminate or conflicting results. Success in imaging of small lesions will depend in part on the development of dedicated imaging devices. Future developments will enable pre- or intraoperative localisation, functional characterisation of breast lesions, and patient follow-up during and after therapy. 

Technetium-99m sestamibi and Technetium-99m tetrafosfamin are used in scintimammography. Scintimammography has excellent sensitivity for tumours larger than about 1 cm; but it does have difficulty detecting smaller, non palpable or medially located lesions. For scintimammography to be accepted as a method that reliably detects small lesions, future developments in producing high-resolution, dedicated gamma cameras is crucial. 

Other applications of scintimammography under study, include the detection of multidrug resistance in breast tumours, stereotaxic prebiopsy localisation of occult breast lesions and detection of axillary lymph node involvement in breast cancer. 

Positron emission tomography (PET) of the breast is based primarily on assessment either of the glucose metabolic rate via 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) or of oestrogen- or progesterone-receptor density with 16[F-18]fluoroestradiol (FES). 

Currently PEM which is Positron Emission Mammography (dedicated units) are already under evaluation for its role in breast cancer.

Breast cancers aggressively accumulate the radiotracer FDG relative to the surrounding tissue. This has been studied in the past decade and as with scintimammography, lesions smaller than 1cm are typically not detected. FDG PET has been evaluated for the staging of recurrent breast cancer and detection of metastases. 

Tumour oestrogen- or progesterone-receptor density is known to be a prognostic factor in patients with breast cancer and can be an important indicator of the potential efficacy of hormone replacement therapies. Approximately two-thirds of breast cancers are oestrogen receptor positive. Tumour uptake level of the radiolabeled oestrogen ligand FES has been shown to correlate strongly with estrogen-receptor content. Furthermore, FES has demonstrated promise as a way of identifying and evaluating the estrogen-receptor content of metastatic tumors of the axillary and mediastinal lymph node chain.
 

Computed Tomography Laser Mammography (CTLM)

This uses laser technology and computer algorithms to produce contiguous cross sectional slice images of the breast. Development of this product began in the late 1980s but computer-processing power was inadequate at that time. Today, the product is under clinical trial. CTLM’s aim is to reduce the number of unnecessary biopsies by helping to determine if a breast lesion is benign or cancerous. This technology is not meant to replace mammography.
 

Summary

The research is promising but it is premature to promote widespread use of non-mammographic breast imaging technologies. These are still considered to be in the early stages of development and may have a high false positive rate if not done correctly. Breast imaging experts like Daniel Kopans, director of the Breast Imaging Division at Massachusetts General Hospital and professor of radiology at Harvard Medical School, believes that we should be cautious and consider everything experimental except mammography and possibly ultrasound.
 

Early Detection
Can Save Your
Life!

Although several new technologies on the horizon show promise
for improved capability
to detect breast cancer, none have yet proved superior to traditional,
X-ray film
mammography in screening for breast cancer.