Grid is a device which is used to improve radio graphic contrasts by reducing scatter radiation. It is first invented by Gustav Bucky in 1913.
Principle of Grid:
Grid is compressed of large numbers of lead stripes separated from each other by some inter spaces material (aluminium) which is penetrable to x-ray.It is designed to transmit only those x-rays whose direction is on a straight line from source to image receptor.While scattered radiation which deviates in a direction from primary beam tends to strike the lead strip and absorbed before reaching the image receptors.
Grid is placed between patient and image receptors so it is efficient devices to reduce radiation.
A typical grid may have lead strip approx.50um thick.Separated by inter spaces material of 3.50um.High quality grid can attenvate 80-95% of scatter radiation.
% of x-ray absorption=Width of lead strip*100
Width of strip+Width of inter space
Grid parameter or factor offering the efficiency of grid.
1.Grid ratio:Grid ratio is the ratio of lead strip to the distance between them.
Grid ratio=h
D
Grid ratio is the parameter widely used to express a grid ability to remove scatter radiation. Grid ratio of 4:1 and 16:1 are available. High ratio grid used for high Kvp technique are more effective to increase contrast on the radiography. It has high patient dose.
Low ratio grid used for low kvp technique grid ratio of 8:1 to 16:1 are generally used for general radiography. Whence as grid with grid ratio 3:1 to 6:1 are used for sub tissue/ mammography examination.
Grid frequency:-It is the number of lead strips per centimeter or inch.
Grid with high grid frequency shows less stripe lines on the radiography.Most of grids have grids frequency about 25-45 lines/om(60-110 lines/inch)
High frequency grids needs high exposure factor, increase patient dose and increase radio graphic contrast.
Grid frequency can be calculated if the thickness of lead strip is Known.
It is calculated by dividing 10m by the sum of the thickness of lead strip and width of inter space.
Grid Material:
Grid strip:The grid strip should be very thin and have absorption capacity.Lead is widely used as grid strip because it has
1)high atomic number,high mass density
2)Relatively inexpensive
3)Platinum, gold, tungsten and uranium have also been tried but none of them is superior then load.
Inter space material:
Aluminium is generally used for inter space material because is has
1)It has suitable atomic number.
2)It is non-hygescopic eg: it does not absorb moisture.
3)It can easily manufacture.
Principle of Grid:
Grid is compressed of large numbers of lead stripes separated from each other by some inter spaces material (aluminium) which is penetrable to x-ray.It is designed to transmit only those x-rays whose direction is on a straight line from source to image receptor.While scattered radiation which deviates in a direction from primary beam tends to strike the lead strip and absorbed before reaching the image receptors.
Grid is placed between patient and image receptors so it is efficient devices to reduce radiation.
A typical grid may have lead strip approx.50um thick.Separated by inter spaces material of 3.50um.High quality grid can attenvate 80-95% of scatter radiation.
% of x-ray absorption=Width of lead strip*100
Width of strip+Width of inter space
Grid parameter or factor offering the efficiency of grid.
1.Grid ratio:Grid ratio is the ratio of lead strip to the distance between them.
Grid ratio=h
D
Grid ratio is the parameter widely used to express a grid ability to remove scatter radiation. Grid ratio of 4:1 and 16:1 are available. High ratio grid used for high Kvp technique are more effective to increase contrast on the radiography. It has high patient dose.
Low ratio grid used for low kvp technique grid ratio of 8:1 to 16:1 are generally used for general radiography. Whence as grid with grid ratio 3:1 to 6:1 are used for sub tissue/ mammography examination.
Grid frequency:-It is the number of lead strips per centimeter or inch.
Grid with high grid frequency shows less stripe lines on the radiography.Most of grids have grids frequency about 25-45 lines/om(60-110 lines/inch)
High frequency grids needs high exposure factor, increase patient dose and increase radio graphic contrast.
Grid frequency can be calculated if the thickness of lead strip is Known.
It is calculated by dividing 10m by the sum of the thickness of lead strip and width of inter space.
Grid Material:
Grid strip:The grid strip should be very thin and have absorption capacity.Lead is widely used as grid strip because it has
1)high atomic number,high mass density
2)Relatively inexpensive
3)Platinum, gold, tungsten and uranium have also been tried but none of them is superior then load.
Inter space material:
Aluminium is generally used for inter space material because is has
1)It has suitable atomic number.
2)It is non-hygescopic eg: it does not absorb moisture.
3)It can easily manufacture.
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