Biomedical Engineering Reference
In-Depth Information
Early detection of breast cancer and timely medical intervention will ensure long-
term survival and an improved quality of life of breast-cancer victims. Early breast
cancers with a higher statistical chance of cure are those which are below 15 mm in
size and found at stage I, when the cancer is confined to the breast. The gold-standard
method of breast imaging is film-screen mammography, which provides very high-
resolution (50
m) X-ray images of compressed breasts. This technology can detect
micro-calcifications of pre-invasive cancer (ductal carcinoma in situ) and both masses
and distortion of parenchyma in small breast cancers with high sensitivity. It has been
used routinely for detecting and characterizing breast disease for 3 decades. However,
X-ray mammography has significant limitations, which include high false-positive
and -negative rates, difficulty in imaging women with dense breasts and inconclu-
sive results. The callback rate of standard screening mammography in community
practice is approximately 8-20 % depending on the screening scenario used. The
false-negative rate with mammography is also significant and ranges from 4 to 34 %,
depending on the clinical context. The relatively poor specificity of mammography
is due to huge overlap in the appearances of a benign disease and early breast can-
cer. Lack of sensitivity of mammography is largely due to obscuration of pathology
by glandular tissue. As a result, mammography is less sensitive for breast cancer
detection in women with radiographically dense breast tissue. This is of particular
concern because there is a significant proportion of dense breasts in both younger
and older women receiving exogenous estrogen. Furthermore, in Asian women, par-
ticularly of Chinese, Korean and Japanese ethnicity, there is a higher incidence of
diffusely dense glandular parenchyma than that in Western, Indian or Malay women
of equivalent age. Other drawbacks of mammography include examinee tolerance
of compression, variability in radiological interpretation and radiation-dose consid-
erations. As a result, there is a clear motivation for the development of alternative
or complementary breast-imaging tools to assist in detection and diagnosis. Other
well-established imaging modalities, such as magnetic resonance imaging (MRI),
positron emission tomography (PET) and ultrasound, are in various stages of use
in diagnosis. However, each of these imaging modalities has its limitations. MRI
exhibits highly variable specificity, ranging from 65 to 90 %, depending on the in-
terpretation technique used and the patient population. Moreover, the cost of MRI
scanners is high and the availability of the technique and the expertise required for
interpretation is very limited. PET scans are even more expensive and scarce; they are
also even more insensitive for both ductal carcinoma in situ and very small cancers.
Ultrasound has difficulty seeing the micro-calcifications produced in early cancers
and is also highly nonspecific for nodules smaller than 1 cm in size. Many small
breast nodules are found in normal women, with a wide range of mostly benign
pathology and neither ultrasound nor mammography is able to distinguish between
these and small cancers with great reliability.
Ultra-wideband (UWB) imaging offers many of the desirable characteristics as
an ideal breast cancer evaluation tool. The method is attractive to patients because
both ionizing radiation and breast compression are avoided, potentially leading to
safer and more comfortable exams. It also has the potential to be both sensitive and
specific, to detect small tumors and to be much cheaper than methods such as MRI
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