is a Women's Imaging Specialist in Chattanooga, TN and the
founder of American Mammographics, Inc.
There have been four screening trials comparing full-field
digital mammography (FFDM) and film-screen mammography (FSM).
None of these trials showed a significant difference in the
diagnostic accuracy between the two in the population as a whole.
The latest trial was the ACRIN study (DMIST), which compared FFDM
with FSM in 42,760 women.
DMIST showed that FFDM had some increased sensitivity in
heterogenously dense or extremely dense breasts (mainly for
Awareness of the limitations of DMIST and the other three trials
will allow more meaningful scrutiny of their results and
conclusions. The various types of bias or limitations in scientific
investigations have recently been comprehensively described.
When a new test is evaluated, its efficacy is determined by
comparing its performance to that of the accepted reference test.
The Kodak Min-R 2000 Screen-Film System (Kodak Health Imaging
Group, Rochester, NY) was used exclusively in the first three
trials and at the majority of the DMIST sites. However, since DMIST
was conducted, there has been significant improvement in
mammographic film-screen technology that now utilizes a
double-emulsion film. The Kodak MIN-R EV Screen-Film System has
replaced the MIN-R 2000 system as the company's premium system.
This means that the new state-of-the-art film-screen technology,
such as the Kodak MIN-R EV System, has become the new reference
standard to which FFDM must be compared. The results of DMIST or
any other comparison study are open to question if the reference
standard is no longer valid.
Optimizing Film-Screen Mammography
The S.O.F.T. Paddle
is one of several recently developed products that can enhance the
performance of FSM. A conventional compression paddle produces
optimum compression of only the thick posterior portion of the
breast. Several compression paddles have been developed that rotate
as compression is applied. They tilt downward over the anterior
breast but, at the same time, they rotate upward posteriorly.
Unfortunately, this causes suboptimal compression of the posterior
breast, which is where most cancers occur.
The S.O.F.T. Paddle
from American Mammographics is different (Figure 1). The
compression surface is horizontal near the chest wall, then curves
slightly to slope downward toward the nipple. It does not rotate.
Increased compression of the anterior two-thirds of the breast is
achieved while maintaining excellent compression posteriorly.
Fibroglandular tissue is spread apart more effectively so that a
cancer is less likely to be obscured by superimposed structures.
There is additional reduction in breast thickness. This permits a
lower kV, which increases contrast. Exposure time is also
shortened, which eliminates motion blur. The improved image quality
with S.O.F.T. Paddle
is shown in Figure 2. S.O.F.T. Paddle
provides many potential benefits, such as increased sensitivity for
cancer detection and fewer callbacks (Table 1).
Dr. László Tabár says of the S.O.F.T. Paddle
, "the image details that are so essential in making the first and
most important decision (callback or normal) are visualized so well
and with such a sharpness as I have never experienced it
New state-of-the-art FSM systems produce higher contrast that
will increase detection of cancers in denser breasts. The Kodak
MIN-R EV system utilizes a new double-emulsion film and a single
improved intensifying screen with smaller, more densely packed
phosphor particles. The new film incorporates many improvements
such as smaller, more uniform cubic silver halide grains in the
primary emulsion, which increases contrast and image sharpness. The
secondary emulsion is designed to increase film latitude to prevent
overexposure of the peripheral breast. Images are sharper and
greater contrast is obtained in dense glandular tissue without
overexposing other areas of the breast. Dramatic improvement in
image quality occurs when the Kodak MIN-R EV system and S.O.F.T.
are used together (Figure 3). Much better contrast and spatial
resolution are achieved particularly in dense tissue, and
remarkably, this is accomplished with less radiation exposure.
Since cancers are most likely to be missed in dense breasts,
better penetrating, higher energy radiation should now routinely be
used for all screening. KV could be increased, but this would
reduce contrast. To produce the higher energy radiation, it is
better to substitute the rhodium (Rh) filter for the molybdenum
(Mo) filter. This will result in a more penetrating beam as well as
shortening the exposure.
An important study in Sweden
showed that the Rh filter provided better depiction of glandular
tissue and the skin for breasts of all size and glandular
composition, while giving a lower dose. Hendrick et al
showed when the Rh filter is used for breasts ≥ 6cm in thickness,
the exposure time is reduced by as much as 30%. The resulting
shorter exposure will reduce motion blur. It will also permit use
of a lower kV, which will increase contrast. The Rh filter also
reduces glandular dose by ≥ 20% in breasts ≥ 6cm in thickness.
Pros and Cons of Digital
The primary motivation for switching to FFDM is not necessarily
the superiority of detector technology but rather the intrinsic
value of the digital image format. This permits images to be
manipulated and transmitted via teleradiology. Patient throughput
also is faster, increasing productivity of technologists. In an
editorial accompanying the DMIST article, Dershaw
recognized several benefits of FFDM but said that these advantages
must be weighed against the cost of FFDM systems (up to five times
as expensive as FSM systems). He also stated "more time and effort
are often required to read digital mammograms than film
A study by Berns et al
showed that digital mammography reduced the time needed to image a
patient by 35% but increased interpretation time by 57%. Monses
said, "Every single one of us at Mallinckrodt was surprised by how
much longer it takes to interpret digital images...I think time
needs to be factored into any cost-effectiveness analysis. This
could become a workforce issue."
Film-screen mammography has been significantly improved by new
products that were not available at the time DMIST and the three
other trials were conducted. The results and conclusions derived
from those trials must not be misused to try to predict the
performance of FFDM compared with the latest state-of-the-art FSM.
Future ACRIN DMIST publications should acknowledge the limitations
of DMIST. This will reassure providers, patients, and third-party
payers that digital and state-of-the-art film-screen mammography
are equally effective for the detection of cancer of the