Digital versus screen film mammography: a clinical comparison
Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
Breast carcinoma is the most common malignancy among women
in developed countries, and its incidence is on the rise in developing
countries. In Malaysia, it accounts for about 30% of newly-diagnosed female
cancers . Imaging of the breast can be traced to its earliest origins in
1913 when a surgeon, Albert Salomon, used radiography images of mastectomy
specimens to demonstrate the spread of breast carcinoma to the axillary lymph
nodes. However it was not until 1960 that the widespread use of mammography
became possible. This was attributed to Robert L. Egan who described a
mammography technique that was reproducible. The first x-ray unit dedicated to
breast imaging was available by 1965. By the 1970s, mammography as a screening
device became standard practice . This was because mammography by then had
been proven to be the most effective method of detecting early breast
carcinoma. The use of mammography in screening of breast carcinoma has been
found to significantly reduce the mortality of this disease .
The transfer of imaging to the digital format began two
decades ago with the introduction of digital radiography. By natural
progression, other imaging modalities then adopted the digital technology. The
transition from conventional mammography to its digital counterpart, however,
was delayed due to the difficulty of producing a full-field digital detector
The first full-field digital mammography unit was approved
for sale by the Food and Drug Administration in 2000 . Since then numerous
hospitals and medical centres worldwide have installed digital mammography
Performance of Digital Mammography (DM)
With any new technology, there is a need to compare its
performance with the known gold standard. Screen-film mammography (SFM) is the
gold standard for breast cancer detection. The SFM technology had been
perfected over the years and mammography unit personnel the world over had been
well trained in this technique. Its quality protocols for breast cancer
detection and screening are also well established. SFM also has a high spatial
resolution well suited for detection of microcalcifications, one of the signs
of early breast carcinoma.
Detection of carcinoma
One of the drawbacks of SFM is its contrast resolution.
The breast is a difficult organ to image as it consists of tissues of
contrasting densities; glandular tissue interspersed with fat. The amount of
glandular tissue varies in different women of different ages, ranging from
dense (in which 75% or more of the breast is occupied by glandular tissue) to
fatty. It has been found that women with dense breasts have a four to six times
higher risk of breast cancer compared to women with little or no glandular
tissue. This is postulated to be due to the masking of existing lesions by the
overlying breast tissue . Therefore the sensitivity of mammography in
detecting carcinoma in dense breasts is limited; a 62.9% reduction in
sensitivity in dense breasts as compared to 87.0% in breasts with fatty
When comparing DM to SFM, it was found that the overall
diagnostic accuracy of both technologies in detecting breast cancer detection was
similar [8, 9]. However, the DM was found to be more accurate in women under
50, women with dense breasts and in premenopausal and perimenopausal women .
This is likely to be due to the wide dynamic range of DM that offers an
advantage over SFM. DM is able to capture areas of contrasting densities and
display these regions without compromising the contrast resolution very much.
As mentioned before, SFM boasts a high spatial resolution
of approximately 16 linepairs per mm which enables detection of fine structures
such as microcalcification. The spatial resolution of DM, however, is limited
by pixel size. Despite this limitation, it has been found that the detection of
microcalcifications on DM is equal to, if not better than, that of SFM [10, 11]
(Figure 1). In a study by Fischer U et al., DM showed more calcification
compared to SFM, having a higher sensitivity and reliability in characterising
microcalcification. This is due to the increased contrast resolution of DM
which enhances its ability to visualise small high-contrast structures such as
The advancement of digital imaging now allows new
techniques of breast cancer detection. Two such techniques that show promise
are contrast-enhanced mammography and tomosynthesis. In contrast-enhanced
mammography, a contrast agent, usually iodine�based, is administered following
an unenhanced image acquisition. As post-contrasted images are acquired (either
using temporal or dual energy technique), these images are subtracted exposing
the pathology in the breast without breast tissue superimposition. In
tomosynthesis, the use of a stationary detector with a moving x-ray source
results in images of the breasts obtained from different angles. Structures
within the breasts are then shifted against each other, again giving rise to
images with less breast tissue superimposition .
Image manipulation and post-processing
Another advantage of DM is the ability to manipulate the
digital information after exposure has been made. With SFM, an image that has
been under- or over-exposed will lose its diagnostic quality and would need to
be repeated. With DM the repeat rate is found to be low .
DM allows for manipulation of the image contrast (Figure
2) and the ability to zoom and magnify (Figures 3 and 4). The overall image
also delineates soft tissue better, especially the subcutaneous skin, an area
that was not well seen on SFM (Figure 5). It is important to realise that
radiologists need to report off the workstation monitors to fully utilise the
ability to manipulate images in DM. This will necessitate training of
radiologists to familiarise themselves from hard-copy to soft-copy reporting.
Another important point to remember is that no amount of image manipulation
could compensate for a mammogram that had been taken using unsuitable exposure
parameters. A good mammogram, be it using SFM or DM, performed by conscientious
radiographers and skilled interpretation by radiologists will yield the optimum
In a recent survey by Haygood et al., it was found that
magnification (72.4% of respondent) is the main tool that is often used by radiologists
while reading a digital mammography examination . It has been suggested
that the use of these computer-based tools such as zoom and magnify may replace
or minimise dedicated compression-magnification view. To date, however, this
has not been proven as computer-based magnification of images contains less
rather than more additional information and hence would not be able to
theoretically replace dedicated compression-magnification views .
Converting from an SFM to a DM system improves the
throughput of mammography cases mainly due to a more efficient workflow .
There is a 45% reduction in the time taken to perform examinations and process
images using DM when compared to SFM . The majority of time saved is in the
abolishment of film processing time . This aspect also proves useful in
interventional breast procedures such as hook-wire localisation, as images can
be viewed immediately on the console without the extra time taken to process
films in between each step of the procedure . Furthermore, hard-copy images
of DM is of a more consistent quality compared to SFM, as the conventional
method of film processing in SFM resulted in variable images sometimes fraught
The time taken to interpret soft-copy DM images has been
found to be longer compared with SFM [14, 16]. This is mainly attributed to the
time taken to manipulate the image by using available tools such as zoom and
magnification on the workstation. However there is no significant difference
when comparing the speed and accuracy of interpretating soft-copy versus
printed-film digital mammography . Difficulty also arises when comparing a
current soft-copy digital examination with a previous SFM examination, as
direct side-by-side comparison is almost impossible. Furthermore, illumination
from a viewing box placed next to a workstation may interfere with the image
display on the workstation . As no consensus has been reached regarding
this problem, it will be up to the individual to decide on the best method to
Image archival, storage and retrieval
In DM, the images are stored in digital format such as on
magnetic optical discs or compact discs. This will considerably reduce the
demand for storage space when compared to SFM. The quality of the images stored
is also preserved as hard-copy images do not degrade due to poor storage
conditions. Transfer of images from remote locations is also possible, opening
the door to teleradiology. With the introduction of PACS (Picture Archiving and
Communication System), the demand for digital imaging increases and the ability
of imaging departments to go film-less is realised, further improving the
standards of healthcare.
One of the prohibitive factors to the advancement of
digital mammography is its cost, estimated to be 1.5 to 4 times higher than SFM
. In a recent study by Tosteson A et al, it was found that while it is
beneficial to screen for breast carcinoma in younger women (especially those
with dense breasts) using digital mammography, the same could not be said for
older women (especially those with non-dense breasts). In the older women,
screen-film mammography may offer better detection of breast carcinoma. Overall
it was found that using all-digital mammography in screening for breast
carcinoma is not cost-effective and that age-targeted digital mammography
screening is the most efficient approach when considering healthcare provisions
. Therefore a balance has to be achieved between desire and reality (the
Digital mammography has been shown to be as good as SFM in
detecting breast carcinoma, and even performs better in women with dense
breasts. DM improves the mammography workflow and therefore increases the
throughput. It does entail a high cost, which is the main prohibitive factor in
its advancement. With robust technological advancement, however, drawbacks could
eventually be overcome, opening the door for DM to replace SFM as the gold
standard for breast cancer detection.
Figure 1 (a) Area of microcalcification seen on the left craniocaudal (CC) view (white circle). (b) Calcifications were better appreciated on compression � magnification view. An associated ill-defined mass was also appreciated (arrows).
Figure 2 (a) A rounded nodule (*) in seen at the inner quadrant in the left craniocaudal (CC) view. (b) The nodule was not seen on the left mediolateral oblique (MLO) view. (c) The nodule (*) was appreciated to be within the subcutaneous tissue following contrast manipulation on MLO and was diagnosed as a sebaceous cyst.
Figure 3 (a) Nodule at right outer quadrant on right CC view (black arrow). (b) Magnification of the nodule shows a rim of lucent halo suggestive of a benign nodule. (c) Ultrasound confirms a benign intramammary lymphnode with a central fatty hilum.
Figure 4 (a) A nodule seen on the right MLO view (arrow). (b) Magnification showed the same nodule to have a spiculated margin suspicious of malignancy. (c) Ultrasound confirms the presence of an invasive ductal carcinoma (biopsy proven) showing a hypoechoiec nodule with a �taller than wide� appearance.
Figure 5 An invasive ductal carcinoma (*) giving a stellate appearance in the left breast on MLO view. There is associated thickening of the skin (white arrows) well appreciated on this digital mammogram.
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|Received 12 February 2008; received in revised form 13 May 2008; accepted 19 May 2008
Correspondence: Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603-79492069; Fax: +603-79494603; E-mail: [email protected] (Yang Faridah A. Aziz).
Please cite as: Faridah Y,
Digital versus screen film mammography: a clinical comparison, Biomed Imaging Interv J 2008; 4(4):e31