REVIEW OF LITERATURE ON DIGITAL MAMMOGRAPHY IN ...

REVIEW OF LITERATURE ON DIGITAL
MAMMOGRAPHY IN SCREENING
Prepared on behalf of the NHSBSP Digital Imaging
Technologies Steering Group by K.C. Young and D. Kitou,
National Coordinating Centre for the Physics of Mammography
NHSBSP Equipment Report 0502
December 2005

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National Coordinating Centre for the Physics of Mammography
Regional Radiation Protection Service
Royal Surrey County Hospital
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Email: ken.young@nhs.net
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CONTENTS
Review of Literature on Digital Mammography in Screening
NHSBSP December 2005 iii
Page No
1. INTRODUCTION 1
2. CLINICAL TRIALS 2
2.1 Colorado Screening Trial I 2
2.2 Colorado Screening Trial II 2
2.3 Oslo I study 3
2.4 Oslo II study 4
2.5 ACRIN-DMIST Trial 5
3. OTHER RESEARCH PUBLICATIONS 7
3.1 Microcalcification detection 7
3.2 Image quality and lesion detection in clinical images 8
3.3 Reasons for disagreement in interpretation of FFDM and SFM 9
3.4 Other techniques in digital mammography 9
4. CONCLUSIONS 12
REFERENCES 13
BIBLIOGRAPHY 15

Review of Literature on Digital Mammography in Screening
NHSBSP December 2005 iv

. INTRODUCTION
NHSBSP December 2005
Review of Literature on Digital Mammography in Screening
It is government strategy in the UK to implement both film-less and paper-less imaging departments by 2006. 1
As a result, there is increasing pressure on and interest from breast screening programmes in moving to digital
mammography. However, screen-film mammography is currently the only accepted imaging technique for
screening, and any changes to the imaging technique should be made only following:
• a review of the available evidence
• consideration of the technical and clinical suitability of the equipment
• assessment of the practical suitability for screening in the UK environment
• assurance that the quality standards of the NHS Breast Screening Programme (NHSBSP) will, as a
minimum, be maintained.
At the beginning of 2005, the NHSBSP set up a steering group for digital mammography to address these
issues. The steering group comprises representatives from the different professional groups and will oversee
the evaluation and introduction of digital mammography for the breast screening programme. This report is
a review of the current scientific literature on digital mammography and concentrates on its role in breast
screening and the evidence for its clinical effectiveness. The five major publications on clinical trials are discussed
in some detail in Chapter 2. Other types of research studies, such as phantom studies, are reported in
Chapter 3. This chapter also reports briefly on the latest literature concerning the development of new imaging
techniques using digital mammography, such as contrast enhancement and breast tomography. Apart from the
major clinical trials, the review is not intended to be fully comprehensive. The proceedings of the biennial
International Workshops on Digital Mammography provide numerous additional research papers that are not
discussed individually here, but are listed in the bibliography.

Review of Literature on Digital Mammography in Screening
2. CLINICAL TRIALS
2. Colorado Screening Trial I
The first results of a trial by Lewin et al 2 were published in 2001. This is referred to here as the Colorado
Screening Trial I, and the main characteristics are summarised in Table 1. The study was performed with a
screening population of 4945 women aged 40 years and older. The aim was to compare full field digital mammography
(FFDM) with screen-film mammography (SFM) for cancer detection. Images were acquired using
both modalities on each woman and were interpreted independently. Findings were evaluated with additional
imaging and, if warranted, biopsy was performed. There were 152 biopsies resulting in the diagnosis of 35
breast cancers. Twenty cancers were detected by SFM and 21 with FFDM. Four cancers were not detected by
either modality but became palpable within a year and represented false negative findings with both modalities.
Thus, no significant difference in the cancer detection rate was observed. FFDM had a significantly lower
recall rate (11.5%) than SFM (13.8%).
Comment: The main finding in this publication was the lack of a significant difference in cancer detection
by SFM and FFDM. However, as the numbers of cancers detected were small, any difference would need to
have been large in order to have been detected. It was also observed that a large proportion of cancers were
detected using one modality but were not detected by the other. Thus, the sensitivity of each modality on its
own seems very low by NHSBSP standards. The specificity of each modality was also low by UK standards
with recall rates of 11–14%.
2.2 Colorado Screening Trial II
The second publication on the results of this trial reported an increase in the number of examinations to 6736
and enabled an analysis of trends with time. 3 In addition, the reasons for the differences in interpretations
between the two modalities were considered. In total, 6736 paired examinations were performed, with 1665
subjects enrolling twice and 291 subjects enrolling three times with an interval of 11 months between examinations.
Symptomatic patients were also imaged but were excluded from the analysis.
The recall rate was 14.9% for SFM and 11.8% for FFDM, which was a significant difference (P < 0.001). The
numbers of cancers detected by the two modalities are compared in Table 2. Eight cancers were not detected
by either modality and were detected by palpation and biopsied within 12 months of the negative screening
findings. These data indicate sensitivities of 66% (33/50) for SFM and 54% (27/50) for FFDM, but these
were not significantly different. The authors indicate that such sensitivities are at or above the expected rate
for their population.
The reasons for cancers being detected by one modality and not the other were examined in detail. No dominant
cause was found. Small differences in the superposition of tissue was one factor cited – and presumed
to be due to slight variations in the projection or compression that were unrelated to the technology in use.
Table Summary of study parameters: Colorado I
Analogue system GE DMR x-ray set with Kodak Min-R 2000 film-screen system
Digital system Prototype of the GE Senographe 2000D with soft copy reading
Patient group Women attending for screening aged above 40
Study type Paired examinations
Number of women 4945
Cancers detected by SFM 22
Cancers detected by FFFM 21
Total number of cancers detected 35
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Table 2 Numbers of cancers with positive and negative screening results for the two modalities
Positive on FFDM Negative on FFDM Totals
Positive on SFM 18 15 33
Negative on SFM 9 8 17
Totals 27 23 50
Differences in lesion conspicuity were also noticed between the modalities – in both directions. Human error
and small differences in interpretation were also factors. The authors highlighted the significantly lower recall
rate with FFDM. However, when they looked at the positive predictive value (PPV), this was similar at 3.3%
(33/1001) for SFM and 3.4% (27/793) for FFDM.
Comment: The main finding in this publication was the lack of a significant difference in cancer detection by
SFM and FFDM. However, as the numbers of cancers were small, any difference would need to have been
rather large in order to have been detected. The numbers of cancers detected by one modality but missed by the
other seemed surprisingly large. One possible conclusion is that relatively subtle differences in presentation can
affect the ability of film readers to detect cancers. It appears that slight variations in compression and view can
mask cancers. This is something that needs to be borne in mind when comparing different modalities. In other
words, it would be preferable to use the same compression and view. Many of the performance parameters (ie
sensitivity, specificity, recall rate and PPV) were quite different from those found in the NHSBSP, suggesting
that caution needs to be exercised in translating such US trial data to the UK context.
2. Oslo I study
In the first Oslo study, 3683 women between 50 and 69 years of age took part in a paired comparison of SFM
and FFDM. 4 The study design is summarised in Table 3. Two standard views of each breast were acquired with
FFDM with soft copy reading and SFM. A total of eight radiologists participated and were divided into two
teams. The teams read the FFDM and SFM images in alternate weeks. The images were read independently
by two radiologists with arbitration by a consensus meeting of the whole team. A five point rating scale was
used for cancer probability, and recall rates, PPVs and cancer detection rates were determined. The mammograms
from prior screening rounds were not offered at the screening interpretation but were available at
consensus meetings. The results are summarised in Table 4, and show that there was no significant difference
in cancer detection rate between the two modalities. The authors conducted a side-by-side analysis of cancer
conspicuity and concluded that the two modalities were equal overall, although one modality or another led
to greater conspicuity in specific cases.
The authors concluded that cancers missed using FFDM (Table 5) were not due to a limitation in image quality
as they were easily visible in retrospect. Rather, they believed that this may have been the result of a learning
effect with the new FFDM soft copy reading environment. They also cited the use of a suboptimal reading
environment (extraneous light sources) as a factor causing cancers to be missed using the FFDM system.
Table Summary of study parameters: Oslo I
Analogue x-ray set Siemens Mammomat 300 using 29 kV Mo/Mo
Analogue film-screen Kodak Min-R 2000 film with Min-R 2190 screen
Digital system GE Senographe 2000D in AOP mode
Digital viewing modality Soft copy reading
Patient group Women attending for repeat screening aged 50–69
Study type Paired examinations
Number of women 3683
Total number of cancers detected 31 (detection rate = 0.84%)

Table Summary outcomes: Oslo I
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Review of Literature on Digital Mammography in Screening
SFM FFDM P-value
Recall rate 3.5% (128/3683) 4.6% (168/3683)
Cancer detection rate 0.76% (28/3683) 0.62% (23/3683) 0.23
PPV for recall on mammographic finding 20% (26/128) 12% (20/168)
Table 5 Numbers of cancers with positive and negative screening results for the two modalities before consensus
meeting
Positive on FFDM Negative on FFDM Totals
Positive on SFM 20 8 28
Negative on SFM 3 – 3
Totals 23 8 31
Comment: The Oslo I study used screening methods quite similar to those used in the NHSBSP, and may
therefore be more readily translated to the UK context than the Colorado studies. As in the Colorado studies,
a number of cancers were missed by each modality, with FFDM tending to miss more (although FFDM and
SFM were not significantly different in this regard). The importance of reader training and viewing conditions
when using soft copy reading were emphasised by the authors, and these are issues that can be taken on
board by the NHSBSP.
2. Oslo II study
The second Oslo study was not a continuation of the Oslo I study, but represented a new study that began five
months after the first one finished. 5 In the Oslo I study, the women underwent both SFM and FFDM, ie it was
a paired study. In the Oslo II study, women attending for screening were randomly allocated to either SFM
or FFDM using the study parameters summarised in Table 6. A total of 25 263 women aged 45–69 attended.
These women were divided into two groups: one for ages 45–49 and the other for ages 50–69. In each group,
the women were randomised to undergo SFM (70%) or FFDM (30%). Two standard views of each breast
were acquired, and independent double reading was performed using a five point rating scale for probability of
cancer. Recall rates, PPVs and cancer detection rates were compared for the two age groups and modalities.
The outcomes for the two age groups are shown in Tables 7 and 8. For both age groups combined, the detection
rate was 0.41% (73/17911) for SFM and 0.59% (41/6997) for FFDM (P = 0.06). The difference in detection
rates between SFM and FFDM was almost significant (P = 0.053) for the 50–69 age group. The recall rate
for FFDM was significantly higher for the 50–69 age group. However, the effect of this appeared to result in
greater cancer detection and similar PPV values for both modalities.
Comment: As with the Oslo I study, the reading methods in the Oslo II study are similar to routine screening
in the UK. Further evidence is provided that screening with FFDM in soft copy mode can yield similar cancer
detection rates to SFM. Recall rates were slightly higher with FFDM, but at levels that would be acceptable
in the NHSBSP. The authors pointed out that prior films were not available during this study, and that they
might have improved the specificity. This study provides the best evidence that a production FFDM system
can be used safely for screening. However, it should be borne in mind that this conclusion may be safely
applied only to this specific model, and after the training and viewing condition issues raised in the Oslo I
study have been addressed.

Review of Literature on Digital Mammography in Screening
Table 6 Summary of study parameters: Oslo II
Analogue x-ray set Siemens Mammomat 300 using 29 kV Mo/Mo
Analogue film-screen Kodak Min-R 2000 film with Min-R 2190 screen
Digital system GE Senographe 2000D in AOP mode
Digital viewing modality Soft copy reading
Patient groups Women attending for repeat screening aged 45–49
Women attending for repeat screening aged 50–69
Study type Randomised allocation SFM/FFDM split 70:30
Number of women 25 263 (attended)
Total number of cancers detected 120 (detection rate = 0.48%)
Table 7 Summary outcomes: Oslo II, age 50–69
SFM FFDM Significance
Recall rate 2.5% (253/10 304) 3.8% (153/3985) P < 0.05
Cancer detection rate 0.54% (56/10 304) 0.83% (33/3985) P = 0.053
PPV for recall on mammographic finding 22.1% (56/253) 21.6% (33/153) NS
NS, not significant.
Table 8 Summary outcomes: Oslo II, age 45–49
SFM FFDM P-value
Recall rate 3.0% (231/7607) 3.7% (112/3012) NS
Cancer detection rate 0.22% (17/7607) 0.27% (8/3012 NS
PPV for recall on mammographic finding 7.4% (17/231) 7.1% (8/112) NS
NS, not significant.
2.5 ACRIN-DMIST Trial
The American College of Radiology Information Network (ACRIN) conducted the Digital Mammography in
Screening Trial (DMIST). 6,7 A total of 49 528 asymptomatic women were screened at 34 centres in the USA
and Canada using the five types of digital equipment shown in Table 9. All women underwent both digital and
screen-film mammography. Two standard views of each breast and any additional views required were taken
with both systems. Each examination was interpreted independently by two separate readers and, depending
on the findings of either study, a work-up was performed. The images were assessed by either hard or soft
copy display depending on what was available with the system, as shown in Table 9. The scales that were
used for the interpretation of the mammograms were a standard BI-RADS scale, probability of malignancy
and a call back scale.
The primary measurements of this study included area under the receiver operating characteristic (ROC) curve,
sensitivity and specificity, PPV and negative predictive value (NPV). Secondary aims of the study are to assess
the effects of patient characteristics such as age, lesion type and breast density on diagnostic accuracy. Finally,
a direct and long term cost-effectiveness analysis of digital mammography is to be performed.
The study showed no significant difference in the diagnostic accuracy between FFDM and SFM for the entire
study population. However, the diagnostic accuracy of FFDM was significantly higher than SFM for three
subgroups, as shown by the areas under the ROC curves in Table 10. The recall rates for SFM and FFDM were
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Review of Literature on Digital Mammography in Screening
both 8.5%. The sensitivities based on 455 days of follow up are shown in Table 11 and are relatively low for both
methods. None of the differences in sensitivity reached a significant level. The authors also calculated higher
sensitivities for a more usual 365 day follow up period. No evidence was found of a difference in diagnostic
accuracy with the type of digital machine. Further publications, including a cost analysis, are promised.
Comment: The DMIST trial is by far the largest clinical trial of digital mammography published to date. It
provides strong evidence that, for the types of digital mammography evaluated, FFDM is no worse than SFM,
and in fact has a significantly better diagnostic accuracy in women aged under 50 and in those with relatively
dense breasts. The recall rate was rather higher and the sensitivities rather lower than would be expected in a
European study. This seems to be the result of differences in the way that screening is carried out in the USA
and Europe. However, the main conclusions could still apply to the UK context.
Table 9 Imaging technique factors and display parameters of the digital systems used 6
Machine
Mean
MGD
type (mGy) Target/filter/kV Grid Soft copy display/monitors
GE 2000D 1.7 Automated optimisation of Yes Two Siemens monitors (each
parameters (Mo/Mo; Mo/Rh
and Rh/Rh)
2 k × 2.5 k)
Fischer 1.8 W/Al/28–35 No: slot Two Barco monitors
scan
design
(each 2 k × 2.5 k)
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Hard copy
display
Not applicable
Kodak
Dryview
8600 or Agfa
LR5200
Fuji 5000MA 2.1 Mo/Mo/28 Yes Not applicable Fuji DryLaser
FM/DPL
Lorad/Trex 2.2 Mo/Mo/25–32 Yes Not applicable Agfa LR5200
Lorad/
Hologic
MGD, mean glandular dose.
2.5 Mo/Mo/25–32 Yes Two Barco monitors
(each 2048 × 2560)
Table 0 Summary of areas under the ROC curves in the DMIST trial
Agfa LR5200
Area under ROC curve
Group (women) No of women SFM FFDM
Significance
All women 42 760 0.74 ± 0.02 0.78 ± 0.02 P = 0.18
Women < 50 years 14 335 0.69 ± 0.05 0.84 ± 0.03 P = 0.002
Women with dense breasts 19 897 0.68 ± 0.03 0.78 ± 0.03 P = 0.003
Premenopausal or
perimenopausal
15 803 0.67 ± 0.05 0.82 ± 0.03 P = 0.002
Table Sensitivities and specificities in the DMIST trial calculated using a 455 day follow up
Sensitivity (± SE) Specificity (± SE)
Group (women)
SFM FFDM SFM FFDM
All women 0.41 ± 0.03 0.41 ± 0.03 0.98 ± 0.001 0.98 ± 0.001
Women < 50 years 0.35 ± 0.06 0.49 ± 0.06 0.98 ± 0.001 0.97 ± 0.001
Women with dense breasts 0.36 ± 0.04 0.38 ± 0.04 0.98 ± 0.001 0.97 ± 0.001
Premenopausal or perimenopausal 0.67 ± 0.05 0.82 ± 0.03 0.97 ± 0.001 0.97 ± 0.001

Review of Literature on Digital Mammography in Screening
. OTHER RESEARCH PUBLICATIONS
3.1 Microcalcification detection
3.1.1 Studies with patients
Fischer et al 8 compared the sensitivity of FFDM and SFM in the detection of microcalcifications and evaluated
their accuracy in microcalcification characterisation. Fifty-five patients with 57 microcalcification clusters
were examined. For each cluster, a screen-film and a digital mammogram were obtained using a GE Senographe
2000D digital system and a GE Senographe DMR with a Fuji UM-MA screen-film system. Evaluation
criteria were image quality, the number of visible calcifications and the characterisation of the findings. For
the characterisation, a five point BI-RADS scale was used where a score of 1 indicated no findings and a score
of 5 was highly suggestive of malignancy. The sensitivity, specificity and image quality scores are shown in
Table 12. The authors reported that FFDM generally detected more calcifications, but that the differences in
specificity and sensitivity for malignant tumours were not significant.
FFDM depicted a significantly higher number of microcalcifications than SFM. More specifically, the number
of visible calcifications was the same for FFDM and SFM in 59% of the cases, whereas FFDM showed more
calcifications in 41% of all cases. There was no case in which SFM showed more particles than FFDM. The
authors concluded that the FFDM system with a 100 µm pixel size provides better image quality, a higher
detection rate and more accurate characterisation of microcalcifications than SFM. 8
Di Nubila et al 9 also investigated how the lower spatial resolution of an FFDM system affects microcalcification
detection. Four radiologists examined the images of 52 surgical samples of non-palpable breast lesions
with microcalcifications taken with both digital (GE Senographe 2000D) and analogue (GE Senographe
DMR) modalities in standard and magnified view. The cases were classified into three groups depending on
the number of microcalcifications in the surgical sample: fewer than 10, 10–30 and more than 30. The Kappa
test was used to evaluate the differences in the numbers of microcalcifications shown in Table 13.
The authors concluded that digital mammography was broadly similar to analogue imaging for standard
views, but appeared to have an advantage when the magnification views were compared. Using a magnification
technique allowed the detection of a larger number of microcalcifications than the standard technique,
with either system.
3.1.2 Studies with phantoms
Rong et al 10 have imaged a phantom containing simulated microcalcifications of various sizes using four different
systems: a flat panel (FP) system (ie as used in the GE Senographe 2000D), a small field-of-view charge
coupled device (CCD) system, a high resolution computerised radiography (CR) system and a conventional
screen-film (SFM) system. The phantom was created using 2 × 2 cm 2 Lucite squares containing simulated
microcalcifications (calcium carbonate grains) at five possible locations. Three different microcalcification
sizes were used ranging from about 120 µm to 160 µm, and three squares were created for each size; the resulting
nine tiles were arranged into a 6 × 6 cm 2 phantom. Scores reflecting confidence ratings were given for all
Table 2 Sensitivity and specificity for malignant tumours with microcalcifications by Fischer et al 8
SFM FFDM
Image quality (points) 3.36 4.25
Sensitivity (%) 91.7 95.2
Specificity (%) 39.3 41.4
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Table Summary of microcalcification count 9
Equal number of
microcalcifications
Larger number of
microcalcifications
Smaller number of
microcalcifications
Digital standard vs
analogue standard
No of
cases %
Digital magnification
vs analogue
magnification
No of
cases %
images, and the results were used to determine the average confidence rating scores of the four systems. ROC
analysis was also performed to assess and compare the detection accuracy of the systems. The areas under the
ROC curves were significantly different, as shown in Table 14.
The results showed that, using either the average confidence rating or ROC analysis, the FP system performed
the best; second was the SFM system; the CCD system was third; and the CR system was last.
Lai et al 11 also compared the ability of different systems to detect microcalcifications. The systems that
were compared were a flat panel (FP), a CCD and a screen-film system using a phantom with simulated
microcalcifications of various sizes (90–355 µm). The images were taken with two different backgrounds
and two magnification modes. A slab of simulated 50% adipose and 50% glandular tissue was used for a
uniform background and an anthropomorphic breast phantom for tissue structure background. To simulate
the microcalcifications, calcium carbonate grains of various sizes were used. For the uniform background,
the size ranged from 90 to 180 µm, and for the tissue structure background from 160 to 355 µm. A phantom
for imaging was formed by two 2 × 2 cm 2 films, with five grains of the same size on each one placed in the
2 × 2 mm 2 region. The FP and CCD images were printed on 8 × 10 inch films using a laser printer. Twelve
viewers were asked to rate the visibility of each microcalcification using a five point scale, where a score of
1 meant definitely not present and a score of 5 definitely present. Using a uniform background and no magnification,
the FP system performed significantly better than the other two. With magnification, the SFM was
similar to the FP, and both outperformed the CCD system. However, with tissue structure background and no
magnification, the FP system was outperformed by the SFM and CCD. With magnification, the FP and CCD
systems improved significantly, with the CCD outperforming both the SFM and FP. These results indicated
that the performance of a mammography system depends not only on the detector technology used but also
on the background structure and magnification.
.2 Image quality and lesion detection in clinical images
Obenauer et al 12 compared clinical FFDM (GE Senographe 2000D) and SFM images from the same patients
using subjective comparisons of image quality and lesion detectability. Digital and conventional mammograms
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Analogue magnification
vs analogue
standard
No of
cases %
Digital magnification
vs digital standard
No of
cases %
141 67.8 147 70.7 178 85.6 132 63.5
37 17.8 52 25.0 24 11.5 62 29.8
30 14.0 9 4.3 6 2.9 14 6.7
Table Areas under the ROC curves for the four modalities
Modality Area under ROC curve (A z ) Standard error in A z
Flat panel 0.857 0.010
Screen-film (SFM) 0.786 0.013
CCD 0.756 0.013
CR 0.683 0.015

Review of Literature on Digital Mammography in Screening
were performed on 55 patients with cytologically or histologically proven tumours. Seventy-five digital mammograms
of patients without tumours were also reviewed along with their screen-film mammograms taken 1.5
years previously. Aspects such as contrast, exposure and the presence of artefacts were evaluated. A three-point
ranking scale was used to judge different details such as the skin and other structures. The detectability and
characterisation of microcalcifications and lesions were also compared and correlated to histology. 12 Artefacts
were found in 78% of the conventional and in none of the digital mammograms. Some anatomical regions
were better visualised by FFDM than by SFM. The authors concluded that digital mammography offers better
image quality without artefacts and equal lesion detection. Lesion characterisation was found to be slightly
better using FFDM even though differences in the final diagnostic decision were not significant.
Fischmann et al 13 performed a study in which 200 women without visible or palpable breast lesions underwent
digital mammography (GE Senographe 2000D) of one breast and SFM of the other. For all women, one
breast was imaged with the FFDM system and the other with the SFM to avoid double radiation exposure
of the breasts. The modalities were allocated randomly and the same compression was applied to both of the
breasts and by the same radiographer. The imaging parameters were set automatically by both systems. Three
readers independently evaluated image quality, visualisation of calcifications and masses under the same
viewing conditions. There was no difference in the diagnostic classification of the microcalcifications, and
also there were no significant differences in the detection of masses. Readers A and B found better contrast
with FFDM in parenchymal tissue, whereas reader C found a better contrast in fatty tissue. All three readers
found the breast parenchyma to be less dense with FFDM. Finally, in contrast to earlier studies, there was a
non-significant tendency for a higher mean glandular dose with FFDM. Digital mammography demonstrated
improved image quality with significantly better depiction of the nipple, skin and pectoral muscle and better
microcalcification detection. 13
Yamada et al 14 compared FFDM (GE Senographe 2000D) with SFM in a study of 24 patients undergoing
surgery or biopsy, including 17 with carcinoma. Three readers evaluated hard copies of a total of 10 masses
and 15 areas of microcalcification in terms of contrast, margin and type. FFDM demonstrated superior or
equivalent contrast of mass, and the same applied in most cases of microcalcifications. The margin of the
mass was better defined in two cases, but both systems were the same when it came to determining the type of
microcalcification. The authors concluded that FFDM might be helpful for detecting masses and determining
their edges but offered no advantages when determining the type of calcification.
. Reasons for disagreement in interpretation of FFDM and SFM
Venta et al 15 studied the causes of disagreement in interpretation between FFDM (GE Senographe 2000D) and
SFM in a diagnostic setting. They concluded that a significant disagreement that affected follow up management
was present in only 4% of breasts. The greatest source of disagreement was found to be the radiologists’ management
approach, which was more significant than differences in lesion visibility between the modalities.
. Other techniques in digital mammography
Digital mammography systems enable the development of new techniques for better breast cancer detection
and diagnosis. Examples are contrast enhanced digital mammography, dual energy contrast enhanced digital
subtraction mammography and tomosynthesis.
3.4.1 Contrast enhanced digital mammography
Contrast enhanced digital mammography utilises the principle that tumour growth and metastatic potential
are directly linked to angiogenesis. 16 Contrast agents are administered and, as they distribute through the
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Review of Literature on Digital Mammography in Screening
blood, x-ray imaging shows increased contrast in the areas where they concentrate. Jong et al 16 have reported
on early clinical experience with this method, suggesting that it may be useful in improving the conspicuity
of lesions in dense tissue. In their study, 22 women who were scheduled for biopsy underwent contrast
enhanced digital mammography. Six sequential images of the affected breast were obtained with a contrast
agent injected intravenously between the time the first and the second image were obtained. Image processing
included registration and logarithmic subtraction.
A number of other studies have also investigated this new technique, concluding that contrast enhanced digital
mammography has the potential of improving the visualisation of breast tumours and that it can be a useful
tool in the detection and differentiation of benign and malignant lesions. 17–20
3.4.2 Dual energy contrast enhanced digital subtraction mammography
Dual energy contrast enhanced digital subtraction mammography is a method of breast angiography. This
technique consists of high and low energy digital mammography after administration of iodinated contrast
agent. Weighted subtraction of the logarithmic transform of the images is then performed and the final image
preferentially shows iodine. 21,22 A study was performed of 26 patients with mammographic or clinical findings
that warranted biopsy. 21 The results showed that 13 patients had invasive cancers, 11 of which enhanced
strongly, one enhanced moderately and one weakly. One patient had ductal carcinoma in situ with the duct
enhancing weakly. In the other 12 patients, benign tissue enhanced diffusely in two and weakly focally in two.
These results indicate that this technique is useful and that further studies ought to be carried out. Another
study compared contrast materials and reached the conclusion that zirconium (Zr) might be a better contrasting
element than iodine for digital subtraction mammography. 22
3.4.3 Tomosynthesis
Tomosynthesis is a method of obtaining three dimensional images of a breast by acquiring a number of low
radiation projection images while the x-ray source of a mammography system moves in an arc above the
Figure Tomosynthesis acquisition geometry. 27
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Review of Literature on Digital Mammography in Screening
breast (Figure 1) either with the detector stationary or with the detector moving in the opposite direction to
the x-ray tube. The individual images can then be reconstructed into a series of high resolution slices. 23 In this
way, different planes of the breast can be displayed, which reduces tissue overlap, making the detectability
of lesions easier. Any plane of the breast can be brought into focus, whereas structures outside this plane are
blurred. 20 With this technique, important morphological information is not lost, making diagnosis easier and
more accurate and, at the same time, reducing the number of recalls and biopsies. The total dose for tomosynthesis
is claimed to be similar to or even lower than that required for standard screening mammography
owing to the elimination of multiple exposures and reduced recalls. 24 Tomosynthesis can play an important
role in screening because it offers the possibilities of reduced breast compression, improved diagnostic and
screening accuracy, three dimensional lesion localisation and contrast enhanced three dimensional imaging. 23–25
Comparisons between tomosynthesis methods and conventional two dimensional mammography have shown
that tomosynthesis exhibits better contrast detail trends and higher detection scores. 25,26
3.4.4 Breast computerised tomography
One of the disadvantages of conventional mammography is that the superimposition of structures sometimes
makes it difficult to detect small carcinomas. Although it is well known that computerised tomography (CT)
is better in terms of contrast resolution than projection radiography by a factor of 10, traditional CT systems
cannot be used for breast screening because of unnecessary irradiation of the thoracic cavity. 28 With cone beam
breast CT (Figure 2), using flat panel detectors, three dimensional breast images could be obtained, resulting in
better diagnostic images without the discomfort of breast compression and without unwanted exposure of the
thoracic cavity. The breast is scanned in the pendulant position with the x-ray tube and detector arrays rotating
around it. The detectors are placed just below the bottom of the shielded table and a swale is engineered
around the area of the breast. In this way, breast tissue close to the thoracic wall and the axilla are imaged,
avoiding unnecessary exposure. 28 A number of tests and simulations have shown that, with a mean glandular
dose equivalent or lower than that of two view screening mammography, breast CT is capable of providing
images with significantly better low contrast detectability of breast tumours and more accurate location of
breast lesions. It has also been shown that objects that are 2 mm in diameter can be easily detected and that
the optimal pixel size of the detector is around 0.2 mm. 28–32
Figure 2 A CT scanner customised for breast imaging. 28

. CONCLUSIONS
Review of Literature on Digital Mammography in Screening
There is now strong evidence in the medical literature that FFDM achieves a diagnostic accuracy in screening
that is at least as good as traditional SFM. Until recently, the published evidence was largely obtained using
General Electric (GE) digital machines, as for the two Oslo trials. However, the recently published DMIST
trial also demonstrated this result using a variety of manufacturers’ products. The DMIST trial is important
because of the large number of women screened. This has allowed the equivalence of FFDM to SFM to be
demonstrated with a much greater precision than in earlier trials. The DMIST trial also demonstrated for the
first time that FFDM can be superior to SFM for important subgroups. The DMIST study reported finding
no difference in clinical results between the different manufacturers’ systems. All of the systems used were
carefully tested to ensure that they met the minimum criteria that apply in the USA.
The authors of the Oslo trial used a methodology that is rather similar to the way in which screening is organised
in the UK, so their results may be particularly pertinent to the UK context. The authors stress the importance
of having good viewing conditions and of following a strict reading protocol. Both of these issues imply the
need for careful training for radiologists switching from analogue to digital imaging. There seems to be no
clear evidence that overall recall rates are likely to be any different from those found using the traditional
equipment. The Oslo II trial reported relatively low recall rates for both SFM and FFDM and, consequently,
high positive predictive values.
NHSBSP December 2005 2

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