IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
Part 19.06: Optimization of protection in
Mammography
Practical exercise
IAEA
International Atomic Energy Agency
Overview
• To be able to apply quality control protocol
to mammography equipment
• To measure, by different methods, the focal
spot size of a mammographic installation
• Interpretation of results
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19.06 : Optimization of protection in Mammography
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IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 19.06: Optimization of protection in
Mammography
Focal Spot Size measurements
IAEA
International Atomic Energy Agency
Focal spot size – Required equipment
1 - Star pattern
2 - Resolution bar
pattern
3- Pinhole and
slit camera
6X magnifying
loupe and
reticule
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Focal spot size
(star pattern) (1)
• The focal spot size measurement is intended to
determine its physical dimensions at installation or
when resolution has markedly decreased. For
routine quality control the evaluation of spatial
resolution is considered adequate
• A magnified X-ray image of the test device is
produced using a mammography screen-film
cassette
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Focal spot size
(star pattern) (2)
1. Select the focal spot size, 28 kV, and an
mAs to obtain an optical density between
0.80 and 1.40 (measured in the central
area of the image)
2. The image should be imaged at the
reference point of the image plane, which is
located at 60 mm from the chest wall side
and laterally centred
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Focal spot size
(star pattern) (2) (cont’d)
3. Remove the compression device and place
the test stand on top of the bucky (breast
table)
4. Place the test device on top of the cassette
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Focal spot size
(star pattern) (2) (cont’d)
• According the IEC norm :
• a nominal 0.3 focal spot should not exceed 0.45
mm in width and 0.65 mm in length
• a nominal 0.4 focal spot should not exceed 0.60
mm in width and 0.85 mm in length
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Focal spot size
(star pattern) (2) (cont’d)
• The focal spot dimensions can be estimated
from the 'blurring diameter' on the image
(magnification 2.5 to 3 times) of the star
pattern
• The distance between the outermost blurred
regions is measured in two directions:
perpendicular and parallel to the tube axis
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Focal spot size
(star pattern) (2) (cont’d)
The focal spot size is calculated as:
x
Dblur
f =
x
180 ( M star - 1)
where :
θ:
the angle of the radiopaque spokes (1° or 0.5°),
Dblur : the diameter of the blur.
Mstar : the magnification factor determined by taking the
ratio of the diameter of the star pattern on the
acquired image (Dimage) to the diameter of the
star pattern (Dstar)
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Focal spot size
(slit camera) (1)
• To determine the focal spot dimensions (f) with a
slit camera, a 10 μm slit is used.
Note: Produce two magnified images
(magnification 2.5 to 3 times) of the slit
perpendicular and parallel to the tube axis.
• The dimensions of the focal spot are derived by
measuring each image using an a 6X magnifying
loupe with a reticule and correcting for the
magnification factor according to: f = F/M
slit
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Focal spot size
(slit camera) (1) cont’d
where:
F:
the width of the slit camera
(Mslit) : the magnification factor determined
by measuring the distance from the
slit to the plane of the film (dslit-to-film)
and the distance from the focal spot
to the plane of the slit (dfocal spot-to-slit)
Mslit = dslit-to-film /dfocal spot-to-slit
NB: The method requires a higher exposure
than the star pattern method.
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Focal spot size
(pinhole) (1)
• To determine the focal spot dimensions (f) with a
pinhole, a 30 μm gold-platinum alloy pinhole is
used.
Note: Produce a magnified image (magnification
2.5 to 3 times) of the pinhole.
• The dimensions of the focal spot are derived by
measuring the image with a 6X magnifying loupe
and a reticule, and correcting for the magnification
factor according to:
f = F/Mpinhole
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Focal spot size
Pinhole camera images of focal spot
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Focal spot size
(pinhole) (1) cont’d
where:
F:
the size of the imaged focal spot.
Mpinhole : the magnification factor determined
by measuring the distance from the
pinhole to the plane of the film
(dpinhole-to-film) and the distance from the focal spot
to the plane of the pinhole (dfocal spot-to-pinhole)
Mpinhole = dpinhole-to-film /dfocal spot-to-pinhole
NB: The method requires a higher exposure than
the star pattern method.
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Where to Get More Information
European protocol for the quality control of the physical
and technical aspects of mammography screening.
http://euref.org/index.php?option=com_phocadownload&
view=category&id=1&Itemid=8
American College of Radiology Mammography Quality
Control Manual, Reston VA, 1999.
Quality Control in Diagnostic Imaging, Gray JE, Winkler
NT, Stears J, Frank ED. Available at no cost.
http://www.diquad.com/QC%20Book.html
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