Mammography Equipment

Question 1

Why are doses kept to ALARA when imaging breast tissue?

Answer 1

Because it is sensitive to ionising radiation and is monitored carefully

Question 2

What are the specific equipment designed to do when imaging breast tissue?

Answer 2

They are designed to give excellent resolution and contrast to allow subtle changes in breast density (and tissue atomic number) to be detected

Question 3

What is mammogram?

Answer 3

A mammogram is an x-ray of the breast used as a screening tool to detect early breast cancer in women with no symptoms at all, it is also used to detect and diagnose breast disease in women with symptoms such as lump, pain, skin dimpling or nipple discharge

Question 4

What are the components of a standard equipment for mammography?

Answer 4

Lower energy x-rays: 24-30 KVP
Smaller focal spot size: 0.1-0.3 mm vs 0.6-1.2 mm
Shorter source - receptor distance: 60-70 cm vs 100 cm SID
Manual/Automatic anode/filter, Exposure factor & Gantry height/ Angulation selection control
Compression plate
AED

Question 5

What is done to fully allow the dose administered is ALARA?

Answer 5

Reject analysis, individual staff performance and recall rates, equipment QA, maintenance and testing all carefully monitored, supervised and adhere to with regular national statistic reporting, additional training, QC and service as required

Question 6

What are the equipment specifications?

Answer 6

Anode materials: Molybdenum, Rhodium (Tungsten)
Filter materials: Molybdenum, Rhodium (Aluminium)
AEC device with posterior, middle & anterior Chambers (+/- lateral & medial chambers)
Quick/easy cassette release from lateral or medial aspect of the bucky (+/- anti ‘double-exposure’ feature)
Hard-wearing, detachable, cleanable bucky
Plastic compression paddle with AEC guide: capable of ~20N (20-25) pressure
Plastic face guard & patient handles

Question 7

What does the dose/ contract depend on?

Answer 7

Breast composition
Equipment use
Patient positioning

Question 8

What are factors to be considered in breast composition?

Answer 8

Atomic number
Size
Shape
Thickness
Density of the tissue

Question 9

What are the aspects of patient positioning ?

Answer 9

Counselling
Preparation
Technique
Compression

Question 10

What should be considered when equipment is being used?

Answer 10

Anode material/ filter selection
Photon energy
Spectrum of the applied x-ray Beam

Question 11

What are the photons energy limits in mammography?

Answer 11

The standard exposures using clinical practise range from 24 to 30 keV
Above 31 keV, the ranges of attenuation of the two tissues types overlap

Question 12

How do you attenuate differences atomic number?

Answer 12

By relying light on photoelectric attenuation of X-rays

Question 13

Why does x-ray photons need to be very small?

Answer 13

The photoelectric absorption is inversely proportional to x-ray energy cubed.
If they are to experience much photoelectrical attenuation in the low atomic number of soft tissues of the breast to x-ray energy cubes energy, the xray photons need to be small but not to the point that they are absorbed in the skin as it will increase the radiation dose

Inversely proportional - as the photoelectric absorption increases the x-ray energy decreases

Question 14

What is a bremsstrahlung process?

Answer 14

It provides a continuous spectrum of x-ray production

Question 15

What is the relationship between the photon energy and the attenuation of the beam?

Answer 15

If the photon energy is too high, too low a proportion of the beam is attenuated and too little absorbed by the breast tissue reducing the radiation dose and reducing image contrast with too much beem penetration

Conversely, photon energy levels must not be so low that too high a proportion of the beam is attenuated and too much is absorbed by the breast tissue increasing radiation dose and reduces image contrast with too little beam penetration

Question 16

What is the process of optimising contrast?

Answer 16

To optimise image contrast we must optimise the photon energy absorption to attenuation ratio
This is achieved by the application of an x-ray beam with a relatively low and narrow photon energy spectrum

Question 17

What is a Focus Spot?

Answer 17

Very small, to reduce your geometric sharpness and maximise images resolution
Low tube KVp values means small focal spot can be used (low tube heating)
Additionally, the node angle may be tilted, in order to obtain a larger effective focal spot (line focus principle)

Question 18

What is the line locus principle?

Answer 18

Increase target angle means actual focal spot size is maintained, but the effective focal spot size is increased this allows use of a very small focal spot which can achieve the required image coverage

Question 19

What is used for the filtration of the beam and how?

Answer 19

Beryllium is used in the ports to allow low energy X-rays to exit.
The beam filtration is essential to eliminate the low energy x-rays that would add to patient dose and scatter
Filters are made of the same target material, this eliminates energies lower or higher than required for producing a nearly perfect beam

Question 20

What is the use of compression?

Answer 20

It allows immobilization, prevents blur/ unsharpness
Reduces and evens tissue thickness (less exposure required to penetrate)
Separation of densities such as superimposition of breast tissue lesions would reduce scatter which in turn would reduce the ionising radiation dose

Question 21

Why is a grid used?

Answer 21

The use of a grid greatly improves radgraphic quality but it does slightly increase the patient dose
It’s used for scatter control which is important as it reduces image quality
Scatter increases for larger and more dense breast with higher KV settings

Question 22

Why is automatic exposure control (AEC) used?

Answer 22

Provides consistent image receptor exposure for various thickness and densities of breast tissue, it is virtually impossible for radiographer to estimate the density /composition of breast tissue therefore an AEC is required as it is an integral part of a mammo equipment

Question 23

Why is magnification used?

Answer 23

To enhance an uncertain area or look at microclassification in more details
Magnification allows increase resolution, reduction in scatter, and improved visibility of detail

Question 24

What is the use of a large SID and why is the anode end of the tube positioned toward the nipple?

Answer 24

A large SID is used to further reduce your geometric unsharpness
Positioning of the anode end of the tube towards the nipple permits a slightly larger x-ray intensity towards the chest wall, using the anode heel effect

Question 25

What is the equipment construction in order?

Answer 25

X-ray tube housing
X-ray tube
Anode
Beryllium window
Filter
Extension cone
Compression paddle
Grid
Cassette
Variable position AEC

Question 26

What is FFDM?

Answer 26

Full field digital mammography - digital imaging
Solid state detectors

Question 27

What is the difference between a mammography unit and a general x-ray unit? - open ended question upon discussion

Answer 27

Mammography requires a much lower KV than conventional radiography common clinical practice uses 24-28 KVP

Mammo also utilises low mA settings which are necessary because of the smaller size anode small focal spot sizes is used

The anode configuration in a mammo x-ray tube produces a prominent heel effect due to the combination of the source to image receptor distance (SID) and the use of an narrow target angle- more concentration at densest area

The effective target angle, measured from the central point, in a mammo tube is 22-24 to achieve a narrower angle and maintain coverage the x-ray tube must be tilted

Anode target is made of molybdenum because it uses the useful photon energy range

Mammo has a relatively short SID of 60 - 76 cms

Beryllium filter in port to remove very low energy photons, and reduce skin dose

Built-in compression device