It is the equipment which uses low energetic x-rays to examine breast for diagnosis and screening.
Prior to the late 1960,s there was no commercially available dedicated mammography equipment .X-ray units with tungsten target which were originally designed for medical imaging procedures such as Chest, Spine radiography.
In 1969 Charles Marie, a physicist and physician at university of Strasbourg experimented with X-ray tube having different anode materials and filters.
Finally in 1969 dedicated mammography were introduced which possess a feature of compression too that identified it as dedicated mammography equipment.
He showed that molybdenum filter/anode can produce better images of breast.
In 1977 dedicated mammography equipment with dual focal spot was introduced (0.09mm and 0.45mm)
X RAY TUBE OF MAMMOGRAPHY
X-Ray tube in mammography operates at low kvp as it minimizes the radiation dose to the breast as glandular tissue of breast is radiosensitive so it is very necessary to use the low radiation dose.
X-ray tube head is angled so as to follow the heel effect. This property is used in mammography by aligning cathode over the chest wall and anode over the nipple area.
The purpose of the filtration in mammography is to remove the higher energetic photons and thus makes the beam monenergetic.
A filter with a k-edge energy just above the characteristic x-rays is used to remove the higher energetic photon.
Molybdenum with a k edge of 20kev is high enough to remove higher energetic photon in mammography.
Cones are required for proper direction of x-ray beam, rejecting scattered radiations thus protecting chest wall and lungs from unnecessary radiation.
With the help of manually adjusted shutters of collimators x-ray field can be more closely matched to the volume being imaged.it plays a great role in spot compression studies.
Compression plate is used to compress the breast which is necessary to have better X-ray penetration which in turn produces clearer images of tissue.
It consists of base with four sides and a bracket attached at one of the sides for moveably mounting the compression plate to an arm, to which x-ray source is also mounted .
The maximum force which can be applied should not be greater than 200N.Standard range is 100 to 150 N.
BENEFITS OF COMPRESSION
Potential benefits of compression includes:
- Uniform breast thickness
- Reduces blurring from patient motion
- Reduces radiation dose
TYPES OF COMPRESSION PLATE
Compression plate is of two types, one is Full compression plate and other is Spot Compression plate.
Full compression plate is used to compress the entire breast and should match the dimensions of image receptor.
Spot compression plate is used to compress the targeted region of breast.
It is flat surface which is used to hold the breast.
All views of breast are obtained by keeping the breast on breast support.
The grid is used in mammography to absorb scattered radiation and improve contrast sensitivity.
As compared to general radiography, grids for mammography possess low grid ratio.
AUTOMATIC EXPOSURE CONTROL
Photo-timers are basically known as AEC devices
The role of photo-timer is to measure X-ray intensity at the image receptor
It consists of single ionisation chamber and an array of three or more semiconductor devices.
When x-rays are transmitted through breast,anti-scatter grid, image receptor ,it generates signal in the detector.
The signal is accumulated and when accumulated signal reaches the preset value, the exposure is terminated