The influence of pressure instead of force on the compression procedure of breasts during mammographic examinations.

There are many complaints concerning the compression procedure in mammography.
Over 25% of the examined women experience moderate to severe discomfort and
pain. At an estimated number of 500 millions compressions per year worldwide a
disconcerting number of complaints. Nearly all interventions have failed to
relieve the number of these complaints (Cochrane 2002). Much research has been
done from the viewpoint that women have differences in pain thresholds and that
could be the reason. But in general women are supposed to have a higher pain
threshold than men. When they sit for example on a chair they experience no
complaints. Whereas the forces they exercise on their rear end and upper legs
are much larger than those that are applied at mammography. Everyone knows the
logic of that; the force is divided over a much larger area. It is remarkable
that this is not taken into account at mammography.

Mammographic paddle and force
At the routinely used technique in compression of the breast a so called
'paddle' is being used, which is down pressed by means of a motor. During the
procedure an increasing force is measured. This force is a reflection of the
counterforce which is experienced by the paddle-arm during the compression
procedure. This force is expressed in dekaNewton (daN), approximately
corresponding to 1 kilogram weight (1 kgf).
The compression is a rather standardized way of working which is, however,
dependent on the experience and the impression of the technician concerning
what the woman can tolerate. The applied force is being monitored and is
maximized (maximum 20 daN). Because of this the desired goal (flatness of the
breast) is realized. When reasoned from the apparatus, this is a reasonable
approach.

Flattening and pressure
From the object which is compressed, however, this is an other story. During
the compression, the breast experiences an increasing pressure. It is
eventually this pressure, which results in the desired flattening of the
breast. The final effect depends on the exercised force and the area on which
that force is exercised (N/m2, Pascal). The size of a woman*s breast can
strongly differ as everyone knows. From a small sample of 50 patients it has
become clear that the volume can differ a factor 10. That means that the
contact area of the breast with the paddle can equally strongly differ during
maximum compression; in this group a factor 4. In the current routine procedure
we measured at the extremes in a number of woman a maximum pressure under 100
mmHg, but we found also women where this pressure can run up to 500 mmHg. It
will be clear that this has large consequences for the desired flattening, and
possibly also for the accompanying complaints.

The aim of the research is during a period of three months, to examine a total
of 500 participants referred for mammography to the AMC. The different
parameters which are relevant to compression will be measured. Particularly the
influence of pressure has never been systematically examined in this respect.
By measuring the discomfort and pain complaints during the advancement of the
compression by means of a visual analog pain scale (VAS) we hope to find a
correlation between the different parameters, to confirm the hypothesis that
the complaints have a relation with the maximum pressure (and no relation with
the force) that is exercised. In addition the pain will be measured with the
Electrical skin impedance (EDA) as an independent physiological parameter for
pain. If the pressure indeed can be connected to a specific moment the pain
arose we would also be able to estimate the total amount of flattening (in mm)
which were reached hereafter by further compression. In this way we hope to be
able to stipulate a cut-off value. The eventual aim is to provide the
mammography machines with pressure sensors to prevent the observed extreme
pressures in the future and as a result of which possibly a large number of
complaints can be prevented. This would also have a positive influence on the
compliance in the screening program.

The patients will be subjected to a normal routine mammographic investigation.
During the research periode one type of paddle will be used.

Technical aspects of the method:
The mammographic machine will be equipped with an (optical) contact area meter.
In the advancement to and during the maximum compression in same period of time
the thickness reduction, incurring force, and the incurring contact area of the
paddle with the breast is measured. These other parameters can are already
measured in the machine itself. From the dynamic force and the contact area
parameters the dynamic pressure range can be calculated.

Pain measurement:
First there is a short introduction and a hand out of the written information.
The radiologists performing the clinical mammography will not be aware if a
woman has given her consent or not.
In advance of the investigation and after written informed consent, the woman
receives a short instruction concerning the use of the continuous
VAS-measurement. In addition the pain will be measured with the Electrical skin
impedance (EDA) as an independent physiological parameter for pain. Directly
after the procedure she is asked for her findings. These are noted.

The measured parameters will be stored directly in a database.

The pain scores will be correlated to the course of the different individual
parameters and combinations of it.

At the informed consent, women will be asked if they are willing to comply to
an telephonic interview which will take a couple of minutes and contains
standard questions about her experiences at 14 days since the mammographic
investigation.

The mammograms will routinely be scored according the clinical BI-RADS lexicon.
The breast density will receive an ACR density score.

The number of prior mammograms will be taken in to account.

The size and thickness of the breasts will be compared to samples from
anonymous data from digital screening units of various regions to trace a
selection bias. This because of the specific profile of the academic population
of the AMC.

Compared to a normal routine mammographic investigation, no extra risk can be
identified.