Mammography
M O D U L E 5 : Mammography Machine (Part 2)
Radiolucent plate that is flat and
COMPRESSION or COMPRESSION PADDLE
parallel to the support should match
A device found in mammographic units the cassette size.
which is used to compress the breast. o To avoid the cut off of an
Flatten out the breast for better image.
visualization of small structure inside of Compression device is
it. approximately 1-4mm thick plastic
Made up of Lexan material; plate.
o Lexan material is made up of
polycarbonate plastic. KINDS OF COMPRESSION
o Transparent and allow the 1. Area of compression – compress
radiation to past through. uniformly.
Polycarbonate material; 2. Spot compression – compress over
o Advantage for using: it is light small specific area of breast, used to
weight. magnify small area for better
Parallel to the receptor visualization.
Improves spatial resolution and reduces
patient dose. TYPES OF COMPRESSION PLATE:
1. Conventional compression plate –
Manually controlled by the RadTech.
not compressed properly.
The approximate diameter of the
2. Never slanted soft paddles – equal
compression paddle is around 5cm or
compression to all areas of breast.
sometimes smaller.
ADVANTAGES:
Approximately 10-20 newton of force or
1. Immobilization of part during exposure
25-40 pounds of pressure is used.
No movement + no motion = good
(similar to the 4 gallons of paints or 18
details of the image.
kg. of rice grains)
2. Gives uniform density
Compression plate a flat surface 3. Reduce geometric un-sharpness
plate = for uniform compression. geometric un-sharpness = Loss of details
Parallel to the receptor surface. 4. Reduce scatter
5. Reduce tissue overlap
6. Enhances recognition of architectural
distortion produce by tumors
DISADVANTAGE:
1. Patient discomfort.
NOTES: It is very important for the compression paddle to have a low attenuation
because if its high attenuation it obstructs the way for x-ray beam.
Mammography
M O D U L E 5 : Mammography Machine (Part 2)
NOTES: The difference of the emulsion layer that is used in the mammography vs. the emulsion layer that is used in
IMAGE RECEPTOR
conventional radiography is that; Mammography use a SINGLE emulsion layer and Conventional uses TWO emulsion layer
Film screen combination – a single
coated/gadolinium oxysulphide film MAGNIFICATION MAMMOGRAPHY
screen combination is commonly used.
Techniques that are used frequently in
o Provide higher film contrast
mammography to produced images up
o Require significantly lower
to twice the normal size.
radiation dose
A zoom-in which aim to focus on one
Current mammography uses single area mainly used to count
emulsion film with combination of microcalcification.
single back screen.
Requires special equipment as
Single screen – thicker intensifying microfocus tubes, adequate compression
screen reduces the spatial resolution or and patient positioning devices.
the availability to see a small structure
which is much needed in ADVANTAGES:
mammography. 1. Magnification of 1.5x to 2x
Cassette size – usually 18x24cm or 2. Increased effective resolution of image
24x30cm receptor
3. Small focal spot size of 0.1mm is used
4 TYPES OF IMAGES RECEPTOR: which also caused the reduction of scatter
1. Direct-exposure film – once used for small
body parts measuring less than 10cm. This DISADVANTAGES:
requires 10-100 times more radiation 1. High patient dose
exposure. This film is no longer used. 2. Longer exposure times
2. Xeroradiography – gives low contrast
images. Useful near the chest wall and AUTOMATIC EXPOSURE CONTROL
doesn’t require grid.
3. Screen film – uses single phosphor screen PHOTOTIMERS
and single emulsion film with cubic grain o Design not to measure x-ray
emulsion. Use of this, results to low patient intensity received by IR but also
dosage and increases image contrast. for x-ray quality.
4. Digital Detector – no film or chemical PURPOSE OF PHOTOTIMER – it
processing used, since it is digital. Its automatically terminates the exposure
phosphor is made of thallium activated once the desire radiation dosage which
cesium iodide. to avoid under exposure that will help in
providing a better x-ray image quality.
Mammography
M O D U L E 5 : Mammography Machine (Part 2)
Also known as AEC device which is
place after the image receptor consist of
single ionization chamber or array of 3 PIXEL SIZE
or more semiconductor diodes.
Preset value corresponds to a specified More applicable in Digital
signal-to-noise ration (SNR) in digital Mammography
mammography or an acceptable optical As pixel size decrease; spatial resolution
density (OD) if film screen system is improves.
used. o The smaller the pixel size the
o Preset value = fixed value better image details
on AEC Pixel size decrease; noise increase
Noise increase; signal-to-noise decrease
TWO TYPES OF AEC
1. Ionization chamber
2. Solid state diode LIMITATION OF MAMMOGRAPHY:
AEC detector is located underneath the 1. Not always certain between benign and
cassette in mammography unlike in malignant tumors
conventional radiography 2. Interpretations of mammograms can be
Thick dense breast – better imaged with difficult because a normal breast can appear
Rhodium target and Rhodium filter differently for each woman.
Thin dense breast = Molybdenum target 3. Appearance of an image may be
and Molybdenum filter. compromised if there is powder or cream on
DOSE LIMITS breast or post-operative cases.
4. Not all types of cancer of breast can be seen
FDA dose limits for screening on mammography
mammograms is around 3mGy with
grid.
Used to evaluate glands, milk ducts and
breast tissues even if there are pathology
to reduce scatter radiation.
Single view, 4.5cm compressed breast
Mammography usually ranges around
18-25 kilovoltage with 1-2 mAs.
