488 G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496
and computed radiography-based mammography using digital
storage phosphor plates (hereafter, DSPM). In FFDM, amor-
phous silicium or selenium ﬂat-panel detectors convert X-rays
into electrical signals . In DSPM, the image is recorded on a
digital storage phosphor plate that is scanned using a laser reader
Although available for more than 5 years, no more than about
10% of accredited mammography facilities use FFDM .
Reasons may include the disadvantage that new purchasers of
FFDM must reconﬁgure all their current X-ray equipment .
of ﬁlm-screen cassettes by DSPM that can be used in a standard
mammography unit . While DSPM has been well-accepted
in Europe and Japan, this system has recently been approved by
the Food and Drug Administration (FDA), and is anticipated to
experience rapid adoption .
Along with economic considerations, the image quality and
the accuracy for the detection and radiological diagnosis of
breast lesions inﬂuences the overall impression of a digital
mammography system. To compare the image quality, lesion
detection, and diagnostic efﬁcacy of FFDM and DSPM, stud-
ies can be designed within either a screening population or a
patient population that allows a correlation of mammographi-
cally suspicious lesions with histologic and follow-up outcome.
However, the use of a screening population would result in a
relatively low number of cancers, which decreases the power
to detect a difference between the modalities and necessitates
studying a large population [13,14].
Therefore, alternatively, we chose to design this prospective
study to compare the image quality, lesion detection, and the
diagnostic efﬁcacy of FFDM and DSPM, based on the classi-
ﬁcation of the American College of Radiology Breast Imaging
Reporting and Data System (hereafter, BI-RADS ). Thus,
150 patients with suspicious breast lesions underwent both
with histologic and follow-up outcome.
2. Materials and methods
2.1. Patients, inclusion and exclusion criteria
This prospective study was approved by the Institutional
Review Board of our University. Written informed consent was
obtained from all patients. From January to June 2003, 150
patients (mean age, 56 years; range, 23–81 years) with sus-
picious lesions (BI-RADS 4) or lesions highly suggestive of
malignancy (BI-RADS 5) on prior mammography, for which a
second opinion was offered at our institution (a referral center),
were included in the study protocol. All of the patients with
lesions that were classiﬁed as BI-RADS 4 or 5 on second opin-
ion were scheduled to undergo core breast biopsy (CBB ) or
surgical excision biopsy of the breast lesions, according to the
patients’ or referring surgeons’ preference. Patients with lesions
classiﬁed as probably benign (BI-RADS 3) on second opinion
were recommended for follow-up at a short interval (6 months).
Patients with mammograms classiﬁed as negative (BI-RADS 1)
or benign (BI-RADS 2) on second opinion were recommended
for follow-up at 1 year after study entry . Exclusion crite-
ria were pregnancy, previous breast implant surgery, and age
younger than 40 years, unless the lesions that required further
evaluation were classiﬁed as BI-RADS 4 or 5.
2.2. Digital mammography
Each of the 150 patients had mammography with both an
FFDM and a DSPM system. Mammograms were performed of
the breasts with the suspected lesions in the craniocaudal (CC)
and mediolateral (ML) views. In total, 300 images were obtained
with each mammography system.
A Senographe 2000D (GE Medical Systems, Milwaukee,
WI., USA) system was used. This system uses an amorphous
silicon ﬂat-detector with cesium iodide as a scintillator. Mam-
mograms were printed on a digital wet laser printer (Scopix LR
5200P, Agfa Leverkusen, Germany). Technical speciﬁcations
are listed in Table 1.
A Mammomat 3000 Nova (Siemens, Erlangen, Germany)
system was used. The digital storage phosphor plate used was
type IP HR V (Fuji, Tokyo, Japan), read by the Image Reader
FMDPL (Fuji). Mammograms were printed on a digital dry laser
printer (DryPix FM-DP L, Fuji). Technical speciﬁcations are
listed in Table 1.
2.5. Mammography quality control
Technical quality controls were performed by a radiolo-
gist, a quality control technologist, and a medical physicist,
according to the tests recommended by the manufacturers of
the digital mammography systems. Daily imaging of the same
mammographic accreditation phantom, used for accreditation of
screen-ﬁlm systems, was performed [17,18].
2.6. Data acquisition
2.6.1. Image Quality
Image evaluation was performed on a viewing box with
a luminance above 3000 cd/m2 (Rotolux 320 DS, Schulte,
Warstein, Germany) in the center, with a difference between
the center and corners of the viewing area of less than 15%
[13,19]. Each of the images was interpreted independently by
ﬁve radiologists with an experience in mammography of 3–6
years. The hard copy images were masked to the edges to pre-
vent glare . Reading conditions were kept constant, with the
ambient room light subdued. To ensure adaptation of the eyes
to the dark, each reading session began with ﬁve trial images
that were similar to the test images, but were not part of the
data analysis. To minimize reading order bias, each radiologist
saw the images in a different random order. The radiologists
G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496 489
Technical speciﬁcations of the digital mammography systems
FFDM Senographe 2000D, GE DSPM Mammomat 3000Nova, Siemens + IP HR V, Fuji
Panel active area (cm) 19.2 × 23 18 × 24
Pixel size (m) 100 50
DQE at 2 lp mm−1 0.6 (30 KV, 14 mAs) 0.3 (28 KV, 14 mAs)
MTF at 1 lp mm−1 (%) 90 62
MTF at 2 lp mm−1 (%) 75 33
Spatial resolution (lp mm−1) 5 9
Wet laser printer Scopix LR 5200P, Agfa Dry laser printer DryPix FM-DP L, Fuji
Spatial resolution (dots/in.) 630 300
Pixel size (m) 40 100
Gray-scale levels 4096 16,384
Resolution (lp mm−1) 12.5 10
Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mammography; DQE, detective quantum efﬁciency; MTF, modular transfer function;
lp mm−1, line pairs mm−1; mAs, milliampere-second; KV, kilovolt.
were free to vary the viewing distance. There were no time con-
straints during the reading sessions . The radiologists were
blinded to the patients’ inclusion and exclusion criteria, to the
image-generating digital mammography system, and to the his-
tologic results of the breast lesions. In order to prevent any bias
regarding the hard copies of each system, the captions on the
ﬁlms were masked with a black tape.
The breast density was assigned according to the classiﬁca-
tion of the BI-RADS-Lexicon: category A, almost entirely fat;
category B, scattered ﬁbroglandular densities; category C, het-
erogeneously dense; and category D, extremely dense . The
readers were asked to compare the images on the basis of the
following nine aspects: brightness; contrast; sharpness; noise;
artifacts (ﬁndings were classiﬁed as artifacts when there was no
correlation of image anomalies to anatomic and/or pathologic
structures, and/or when image anomalies were seen on a portion
of the ﬁlm without breast tissue imaged); and detailed detection
of anatomic structures, i.e., skin, retromamillary space, glandu-
lar tissue, and the detection of calciﬁcations. Each of the nine
aspects was categorized using a ﬁve-level scale (1, excellent; 2,
good; 3, moderate; 4, poor; 5, not acceptable).
2.6.2. Lesion detection and diagnostic efﬁcacy
126.96.36.199. Lesion detection. In case of breast lesions, lesion size
(maximum diameter on mammograms) and characteristics, i.e.,
mass and/or calciﬁcations, architectural distortion, and asym-
with an experience in mammography of 6 and 10 years, respec-
tively, in an unlabeled, random order. In cases of discrepancy,
conclusions were reached by consensus in the presence of a third
experienced radiologist. The reading conditions were identical
to those described above.
188.8.131.52. Diagnostic efﬁcacy. The diagnostic efﬁcacy was
assessed by the two radiologists who interpreted the lesion
detection session, based on the classiﬁcation of the BI-
RADS-Lexicon: 1, negative; 2, benign; 3, probably benign; 4,
ing to a diagnostic, but, in contrast to a screening situation,
the BI-RADS categories 1–3 corresponded to benign diagnoses
and the BI-RADS categories 4 and 5 corresponded to malignant
184.108.40.206. Diagnostic efﬁcacy for malignant lesions. In particu-
density categories with FFDM and DSPM was compared.
2.6.3. Histologic and follow-up correlations
Of 150 patients, 121 (80.7%) (mean age, 51 years; range,
23–78 years) with lesions classiﬁed as category BI-RADS 4 or
5 on either FFDM or DSPM underwent CBB (n = 98), or sur-
gical excision biopsy (n = 23). Those with malignant histologic
results on CBB underwent surgical excision, as did those with
benign results, according to the patients’ or referring surgeons’
preference. The histologic results were compared to the image
features in a multidisciplinary review.
Of 150 patients, 29 (19.3%) (mean age, 58 years; range,
30–81 years) with lesions classiﬁed as category BI-RADS 1,
2 or 3 had follow-up for at least 2 years after study entry.
220.127.116.11. Statistical analysis. Statistical analysis was performed
using commercially available software (SPSS for Windows,
Realease12, SPSS Inc., Chicago, IL, USA).
For the comparison of image quality, the signiﬁcance of dif-
ferences between FFDM and DSPM was determined using the
Wilcoxon test . In addition, the mean, the standard deviation
(S.D.), and the level of signiﬁcance of the rating data of the ﬁve
radiologists was assessed for each of the nine aspect of image
For the diagnostic efﬁcacy, the interrater agreement was
ment was deﬁned as almost perfect, > 0.8; good, = 0.8–0.61;
moderate, = 0.60–0.41; fair, = 0.4–0.21; or poor, < 0.20
. McNemar’s test was performed to evaluate whether the
differences between FFDM and DSPM, with regard to the
diagnostic efﬁcacy, were signiﬁcant . For all tests, the sig-
niﬁcance level was set to p < 0.05 .
490 G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496
Ratings of image quality
Image quality FFDM Senographe 2000D, GE DSPM Mammomat 3000Nova, Siemens + IP HR V, Fuji P-value
Brightness 1.73/0.29 1.80/0.32 n.s.
Contrast 1.54/0.39 2.09/0.35 <0.05
Sharpness 1.45/0.32 1.90/0.38 <0.05
Noise 1.40/0.27 1.49/0.41 n.s.
Artifacts 1.32/0.21 1.38/0.30 n.s.
Skin 1.50/0.49 2.31/0.38 <0.05
Retromamillary space 1.55/0.42 2.05/0.30 <0.05
Glandular tissue 1.64/0.42 1.99/0.42 <0.05
Calciﬁcations 1.44/0.40 2.08/0.71 <0.05
Each aspect was categorized using a ﬁve-level scale ((1) excellent; (2) good; (3) moderate; (4) poor; (5) not acceptable). The mean/standard deviation and the level
of signiﬁcance are indicated. Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mammography; n.s., not signiﬁcant.
For FFDM and DSPM, sensitivity was calculated as
TP/(TP + FN), speciﬁcity was calculated as TN/(TN + FP),
PPV was calculated as TP/(TP + FP), and NPV was calcu-
lated as TN/(TN + FN), and diagnostic accuracy was calculated
as (TN + TP)/(TP + TN + FP + FN), with TP = true positive,
FN = false negative, TN = true negative, and FP = false positive.
3.1. Image quality
Of 150 patients, 14 (9.3%) were rated with a breast density of
category A, 64 (42.6%) of category B, 71 (47.4%) of category C,
and one (0.7%) category D with FFDM, compared to 14 (9.3%),
51 (34%), 84 (56%), and one (0.7%) with DSPM.
Of a total of 6750 image quality scores per digital mam-
mography unit (150 patients, 9 scores, 5 readers), 4047 scores
(59.96%) rated an excellent, 2019 scores (29.91%) a good, 505
scores (7.48%) a moderate, 163 scores (2.41%) a poor, and 16
scores (.24%) rated an unacceptable image quality for FFDM.
(23.84%) a good, 1529 scores (22.65%) a moderate, 422 scores
(6.25%) a poor, and 68 scores (1.01%) rated an unacceptable
image quality (Fig. 1). For the mean, standard deviation, and
level of signiﬁcance, see Table 2. For each comparative aspect,
except brightness, noise, and artifacts, FFDM was rated signiﬁ-
images in any of the aspects.
3.2. Lesion detection and diagnostic efﬁcacy
3.2.1. Lesion detection
A total of 74 mass lesions (mean size, 16 mm; range
3–90 mm) were seen with FFDM (circumscribed, n = 2; indis-
tinct, n = 48; spiculated, n = 24), compared to 80 mass lesions
(mean size, 18 mm; range 3–90 mm) seen with DSPM (circum-
scribed, n = 5; indistinct, n = 49; spiculated, n = 26); see Table 3,
and Fig. 2.
A total of 85 lesions consisting of calciﬁcations (mean size,
15.1 mm; range 2–60 mm) were seen with FFDM (benign, n = 4;
amorphous, n = 3; pleomorphous, n = 65; linear, n = 13), com-
pared to 75 calciﬁcations (mean size, 15.5 mm; range 3–50 mm)
with DSPM (benign, n = 8; amorphous, n = 1; pleomorphous,
n = 59; linear, n = 7); see Table 3, and Fig. 3. Within these 85
lesions, lesions that consisted of mass lesions as well as cal-
ciﬁcations were seen with FFDM in 35 and with DSPM in 23
Architectural distortion or asymmetric density was not
3.2.2. Diagnostic efﬁcacy
With FFDM, BI-RADS 1 was rated in seven cases, BI-RADS
2 in one case, BI-RADS 3 in 21 cases, BI-RADS 4 in 81 cases,
and BI-RADS 5 in 40 cases, compared to ﬁve, nine, 17, 76, and
43 cases, respectively, with DSPM; i.e., malignancy was sus-
pected in 121 cases with FFDM and in 119 cases with DSPM;
see Table 3, and Figs. 2 and 3. Interrater agreement was almost
perfect (0.80) for FFDM, and good (0.78) for DSPM. The dif-
ference in diagnostic efﬁcacy between FFDM and DSPM was
not signiﬁcant (p = 0.86).
Lesion detection and diagnostic efﬁcacy, based on the classiﬁcation of the
American College of Radiology Breast Imaging Reporting and Data System
3000Nova, Siemens + IP
HR V, Fuji
Mass circumscribed 2 5
Indistinct 48 49
Spiculated 24 26
Total 74 80
Calciﬁcations benign 4 8
Amorphous 3 1
Pleomorphous 65 59
Linear 13 7
Total 85 75
BI-RADS 1 7 5
BI-RADS 2 1 9
BI-RADS 3 21 17
BI-RADS 4 81 76
BI-RADS 5 40 43
Number of patients, n = 150. Note: FFDM, full-ﬁeld digital mammography;
DSPM, digital storage phosphor mammography.
G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496 491
Fig. 1. Comparison of image quality. Right craniocaudal (CC) and mediolateral (ML) mammogram views of a representative patient (49-year-old woman with breast
density category C according to the classiﬁcation of the BI-RADS-Lexicon) are shown; (A) FFDM CC; (B) FFDM ML; (C) DSPM CC; (D) DSPM ML. The image
quality aspects contrast, sharpness, and detailed detection of anatomic structures (skin, retromamillary space, and glandular tissue) were rated slightly better for
FFDM than for DSPM. The aspects brightness, noise, and artifacts were rated equal.
3.2.3. Diagnostic efﬁcacy for malignant lesions
With FFDM, three BI-RADS 4 and 5 mass lesions (mean
size, 14.8 mm; range, 3–20 mm) were seen in breast density cat-
egory A, 19 (mean size, 21.8 mm; range, 8–90 mm) in breast
density category B, 21 (mean size, 18 mm; range, 10–48 mm) in
breast density category C, and zero in breast density category D,
compared to seven (mean size, 15.8 mm; range, 3–30 mm), 24
(mean size, 20.2 mm; range, 6–90 mm), 24 (mean size, 20.2 mm;
range, 8–50 mm), and zero with DSPM; see Table 4.
With FFDM, ﬁve (mean size, 14.9 mm; range, 4–35 mm) BI-
RADS 4 and 5 lesions consisting of calciﬁcations were seen
in breast density category A, 17 (mean size, 16.8 mm; range,
3–60 mm) in breast density category B, 27 (mean size, 15.7 mm;
range, 2–60 mm) in breast density category C, and zero in breast
density category D, compared to three (mean size, 14.4 mm;
range, 3–30 mm), 12 (mean size, 16 mm; range, 3–50 mm), 29
(mean size, 17 mm; range, 3–50 mm), and zero with DSPM; see
BI-RADS 4 and 5 lesions that consisted of mass lesions as
well as calciﬁcations were found in breast density category A,
B, C, and D in one (mean size, 12.5 mm; range, 5–25 mm), 16
(mean size, 20.5 mm; range, 7–42 mm), 11 (mean size, 19.5 mm;
range, 10–40 mm), and one case (size, 20 mm) with FFDM,
as compared to one (mean size, 12.5 mm; range, 5–25 mm),
492 G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496
Fig. 2. Lesion detection and diagnostic efﬁcacy: mass lesion. Left mediolateral mammogram views of a representative patient (65-year-old woman with breast
density category A according to the classiﬁcation of the BI-RADS-Lexicon) are shown; (A) FFDM; (B) DSPM. An irregular, spiculated, high-density mass (size,
21 mm) was detected in the upper portion of the breast. The lesion was rated BI-RADS 5 with both FFDM and DSPM. The lesion was found to be invasive cancer
at histology. Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mammography.
nine (mean size, 22.0 mm; range, 9–45 mm), nine (mean size,
19.0 mm; range, 10–38 mm), and one (size, 20 mm) case with
DSPM; see Table 4.
3.3. Histologic and follow-up correlations
The histologic results of CBB and surgical excision biopsy
were malignancy in 77 cases (invasive carcinoma, n = 51; ductal
carcinoma in situ, n = 26), and benign lesions in 44 cases. Each
malignant result of CBB histology was conﬁrmed by surgery.
Follow-up in 29 cases yielded no suspicious breast lesions.
Assessment of the diagnostic efﬁcacy of BI-RADS 4 and 5 lesions, based on the
classiﬁcation of the BI-RADS-Lexicon in breast density categories A through
Mass Calciﬁcations Mass
A 3/7 5/3 1/1 9/11
B 19/24 17/12 16/9 52/45
C 21/24 27/29 11/9 59/62
D 0/0 0/0 1/1 1/1
Total 43/55 49/44 29/20 121/119
The numbers of breast lesions diagnosed with FFDM/DSPM are shown. Note:
FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mam-
Accordingly, FFDM encountered 77 TP, 29 TN, 44 FP, and 0
FN results; DSPM encountered 75 TP, 29 TN, 44 FP, and 2 FN
Both false-negative results with DSPM were lesions that
consisted of pleomorphous calciﬁcations (size, 3 mm each) in
patients with a breast density category of B, which were rated
BI-RADS 4 with FFDM. The same calciﬁcations were rated BI-
RADS 2 with DSPM. Both lesions were found to be invasive
cancer at histology (Fig. 4).
The results of sensitivity, speciﬁcity, PPV, NVP, and accuracy
of FFDM and DSPM are listed in Table 5.
Number of patients, n = 150
3000Nova, Siemens + IP HR
Sensitivity 1.0 (0.953/–) 0.974 (0.909/0.997)
Speciﬁcity 0.397 (0.285/0.519) 0.397 (0.285/0.519)
PPV 0.636 (0.544/0.722) 0.630 (0.537/0.717)
NPV 1.0 (0.881/–) 0.935 (0.786/0.992)
Accuracy 0.707 (0.627/0.778) 0.693 (0.613/0.766)
Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor
mammography; PPV, positive predictive value; NPV, negative predictive value;
lower/upper values of conﬁdence intervals in brackets.
G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496 493
Fig. 3. Lesion detection and diagnostic efﬁcacy: calciﬁcations. Left mediolateral mammogram views of a representative patient (69-year-old woman with breast
density category A according to the classiﬁcation of the BI-RADS-Lexicon) are shown; (A) FFDM; (B) DSPM. A lesion that consisted of clustered pleomorphous
calciﬁcations (size, 20 mm) was detected in the retromamillary space (white circles). The lesion was rated BI-RADS 4 with both FFDM and DSPM. The lesion was
found to be invasive cancer at histology. In addition, linear calciﬁcations that are associated with tubular structures were slightly better detectable with FFDM. They
were rated as benign vascular calciﬁcations with both systems. Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mammography.
Radiologists usually compare the image quality of different
mammography systems with non-objective aspects. The most
important are brightness, contrast, sharpness, and noise .
Our data show that FFDM provides a superior image quality
to DSPM. For six of nine scores of image quality, including
contrast and sharpness, signiﬁcantly better results for FFDM
were noted, while for brightness and noise, both systems were
equal (Table 2). In addition, FFDM is superior to DSPM in the
Fig. 4. False-negative result with DSPM. Left mediolateral mammogram views of a representative patient (55-year-old woman with breast density category B
according to the classiﬁcation of the BI-RADS-Lexicon) are shown; (A) FFDM; (B) DSPM. A lesion that consisted of pleomorphous calciﬁcations (size, 3 mm) was
detected in the central portion of the breast (white circles). It was rated BI-RADS 4 with FFDM. The same lesion was rated BI-RADS 2 with DSPM. The lesion was
found to be invasive cancer at histology. Note: FFDM, full-ﬁeld digital mammography; DSPM, digital storage phosphor mammography.
494 G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496
detailed detection of anatomic structures of the breast (Table 2),
as well as in the detection of breast lesions consisting of calci-
ﬁcations (Table 3). However, our data demonstrated that FFDM
and DSPM were equal in diagnostic efﬁcacy, with compara-
ble values of sensitivity, speciﬁcity, PPV, NPV, and accuracy
(Table 5). Notably, in patients with breast density categories of
C and D, no differences in diagnostic efﬁcacy were observed
Our data may be of interest, since this is the ﬁrst study that
compares the image quality, lesion detection, and diagnostic
efﬁcacy of FFDM and DSPM in a clinical setting. The study
both FFDM and DSPM, as well as enabling the correlation of
mammographic lesion aspects with histologic and follow-up
In our study, markedly more breasts were classiﬁed with a
breast density category of B with FFDM, and, conversely, as a
breast density category of C with DSPM. We suggest that, most
likely, this is due to the observed superior detailed detection of
ﬁbroglandular tissue in dense breasts with FFDM, leading to a
downward categorization of breast density.
By revealing that digital mammography has signiﬁcant ben-
eﬁts over ﬁlm-screen mammography, especially in breasts with
density categories of C and D, where the sensitivity of the tradi-
tional technology is somewhat limited , the study by Pisano
et al. has already begun to increase the demand for digital mam-
mography among clinicians and patients [2,5]. Notably, in our
study, DSPM was proven to be similarly effective as FFDM
in the detection of BI-RADS 4 and 5 mass lesions in patients
with dense breasts. In our opinion, the fact that, overall, six
mass lesions more were suspected with DSPM than with FFDM
(Table 3), can, at least in part, be explained by the superior
detailed detection of ﬁbroglandular tissue and, hence, a better
differentiation between ﬁbroglandular tissue and mass lesions
Differences, however, were noted in the detection of cal-
ciﬁcations. In contrast to previous data that showed an equal
detection of calciﬁcations for different digital mammography
systems [24,25], in our study, with FFDM, more calciﬁcations
were detected than with DSPM (85 versus 75; Table 3). While
the number of detected BI-RADS 4 and 5 lesions that consisted
of calciﬁcations was comparable in patients with a breast den-
sity of C or D with FFDM and DSPM (27 versus 29; Table 4),
a breast density category of A or B (22 versus 15; Table 4). This
can, in part, be explained by the fact that, with DSPM, a smaller
number of breasts were classiﬁed with a density category of A
or B than with FFDM (65 versus 78). As a consequence, some
of the detected lesions that consisted of calciﬁcations in breasts
of density category A or B with FFDM were, with DSPM, in
fact, detected in breasts of a density category of C or D.
Furthermore, DSPM yielded two false-negative results. Both
lesions consisted of calciﬁcations in patients with a breast den-
sity category of B. Both lesions were displayed by both FFDM
and DSPM. Notably, they were rated BI-RADS 4 with FFDM,
whereas, with DSPM, they were rated BI-RADS 2 (Fig. 4). Both
lesions proved to be invasive carcinoma. In our opinion, these
data show that the perception and characterization of breast
lesions is not solely dependent on the digital mammography
system, but is strongly inﬂuenced by the interpretation of the
radiologist, rendering the radiologist one of the major determi-
nants in breast imaging. This dilemma has also been reported
by others [26–28].
However, basically, the superior depiction of ﬁbroglandular
tissue details with FFDM, and the differences in the detection of
calciﬁcations that favored FFDM in our study, are most likely to
be considered an effect of differences in the detective quantum
and MTF are the most well-known methods for the objective
assessment of differences of mammography systems . DQE
is the measure of the combined effect of the image noise and
the contrast of an imaging system, expressed as a function of
object detail. The FFDM system has a higher DQE than DSPM
(Table 1). This allows for better contrast resolution of structures
at a spatial resolution of 1–4 line pairs mm−1 (lp mm−1), where
the human eye performs best . MTF is the measure of the
ability of an imaging system to render the contrast of an object as
a function of object detail. The FFDM system has a much higher
the cesium iodide scintillator, which produces higher-resolution
images than the DSPM .
The assumption that digital mammography would require a
spatial resolution similar to that of ﬁlm-screen mammography
(at least 10 lp mm−1 required in Europe ) has recently been
proven to be a misconception . Equally, in the comparison of
the digital mammography systems in our study, the lower spatial
resolution of 5 lp mm−1 for FFDM versus 9 lp mm−1 for DSPM,
is not arbitrative (Table 1). Considering the superior results of
the image quality for FFDM in our study, the better DQE and
MTF seem to compensate for the lower spatial resolution of
FFDM compared to DSPM.
The interrater agreement for diagnostic efﬁcacy, based on
the BI-RADS classiﬁcation, was almost perfect for FFDM
( = 0.80), and good ( = 0.78) for DSPM. Recently, Berg et
al.  reported interrater agreement for the BI-RADS classi-
ﬁcation to be as low as 0.41–0.44, even subsequent to a short
BI-RADS training session. The authors evaluated the diagnostic
efﬁcacy of 23 practicing mammogram-interpreting physicians.
In contrast, in our study, the mammograms were examined by
two experienced radiologists using the BI-RADS system over
several years. This may explain the differences in the interrater
agreement between our study and the results reported in the
Our study suffers from several limitations. First, the per-
formance of the lesion detection and diagnostic efﬁcacy may
have been biased: although the study was designed to blind the
readers to the patients’ inclusion and exclusion criteria and to
the histologic results of the breast lesions, the readers might
have been more aware of breast lesions, since only the unilat-
eral breasts with suspicious lesions were imaged. Therefore, it
may be debated whether the number of suspected lesions, as
well as the number of false positive lesions (n = 44/150), might
have been smaller if the readers would have encountered the
mammograms of both breasts. However, additional imaging by
G. Schueller et al. / European Journal of Radiology 67 (2008) 487–496 495
both digital systems of the contralateral breast without suspected
lesions would have been against ethical principles.
Second, the determination of subjective aspects of image
quality, as well as lesion detection, was based on visual assess-
ment, which is inﬂuenced by individual observer characteristics
and subjective criteria. We tried to decrease the effect of indi-
vidual observer preferences by including ﬁve radiologists for
the evaluation of the image quality scores. However, we chose
to summarize the subjective rating scores for each aspect of the
image quality across all ﬁve radiologists to minimize the effect
of reader variability. statistics were not applicable because of
the asymmetric distribution of the rating scores for the aspects
of image quality .
Third, although one of the major advantages of digital over
ﬁlm-screen mammography is the possibility of soft-copy read-
ing, in this study, both FFDM and DSPM images were printed
and compared under the same viewing conditions. With post-
processing, soft-copy review may have altered the results of the
image quality scores for both systems, as described recently
[34,35]. However, at the time of image interpretation, no digi-
tal monitor was commercially available that could provide the
recommended spatial resolution for soft-copy reading for one
of the systems. However, we do not believe that the use of soft-
copy reading would have altered the almost identical results
of the diagnostic efﬁcacy for both systems, and of course the
conclusion drawn for our data.
Fourth, FFDM images were printed on a digital wet laser
printer, and DSPM images on a digital dry laser printer. How-
ever, we do not feel that the difference in the printer devices has
inﬂuenced our results. Notably, no signiﬁcant differences were
observed in the rating of image artifacts. This is in accord with
previous data that observed equal image quality and diagnostic
efﬁcacy of wet and dry laser printers in digital mammography
In conclusion, the data from this prospective study, which
compared the image quality, lesion detection, and diagnostic
efﬁcacy of FFDM and DSPM by histologic and follow-up corre-
lation of breast lesions, provide better results for FFDM in image
quality, and in the detection of lesions that consisted of calci-
ﬁcations. However, diagnostic efﬁcacy was equal for the two
systems. Particularly in patients with breast density categories
of C and D, where digital mammography is a ray of hope in the
detection of breast lesions, no differences in diagnostic efﬁcacy
were observed. Based on the interpretation of the false-negative
results, our data suggest that the perception and characterization
of breast lesions is not deﬁned solely by the digital mammo-
graphic system: it is essentially inﬂuenced by the radiologist,
who is one of the major determinants in the interpretation of
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