Future Directions in Breast Imaging
(updated 1 January 2006)

Diffraction Enhanced Breast Imaging (DEBI)

Tumour cells (such as breast cancer cells) have a diffractive effect on X-rays. They scatter them in various directions but most strongly at 9 degrees from the main X-ray beam. Robert Speller and a team at University College London are developing a new form of mammogram that can detect tumours only 4mm wide. This is advantageous because current mammography particularly in younger women with dense breasts have difficulty spotting cancers less than 10mm in diameter. The smaller the cancer at detection, the less likely it has spread and the easier it is to excise. Early tests on excised breast tissue are promising. The challenge currently is to build an extra detector and extra electronics for analysis into existing mammography systems.
 

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.

Further studies may still be needed to see if it will significantly improve accuracy in the early detection of breast cancer in general to justify its extra costs over conventional mammography.  

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.

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.
 

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). 

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.

As is the case for scintimammography, future improvements in PET of breast cancer will include the development of dedicated image acquisition systems to enable detection of smaller lesions.
 

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.
 

T-scan technology

This imaging technology is based on electrical impedance. The TransScan TS-2000 product emits very small electrical signals, which are sent through a wand held by the patient. A scanning probe completes the electrical circuit and a computer instantly reconstructs the signals to create a detailed image of the breast received through the probe. 

Cancer cells tend to be good electrical conductors and therefore, to show up on the image. As the TransScan machine is portable, it may prove to be a promising alternative in the future.
 

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.