Back to Basics | X-Ray Grids
Back to Basics | X-Ray Grids
What is a Grid?
A grid, fully named an “X-Ray Antiscatter Grid,” is comprised of alternating lines of lead and another, much more X-ray transparent material, that is put directly in front of the detector or film. The purpose of them is to remove x-rays that have scattered and are not moving in a direct line from the X-ray tube to the detector.
When Do I Need a Grid?
Grids provide value when used with body parts of 10cm (4”) of thickness or more. The thicker the body becomes, the more important the grid is.
This is because grids remove scatter created as the X-ray moves through the body, and the more body it moves through, the more scatter is created.
On a thin body part, removing the grid can reduce the amount of X-ray you need for a good image. On a thick body part, this is not true. This is because while more X-rays reach the film or detector without the grid, a much larger % of those X-rays are scatter, ruining the image.
As a rule of thumb, grids are required for chiropractors, orthopedists, imaging centers and hospitals and optional for veterinarians, and unnecessary for podiatrists and hand specialists.
Not All Grids are the Same #1
Interspacer:
X-ray grids can have different interspacers, which are the more transparent material between the lead. For dealers, 99% of the grids will be Aluminum interspacers because of their durability and lower cost. There are also fiber (paper) interspacers used in Flouroscopy and mammo, and JPI makes a grid exclusively for mammo using solid carbon interspacers.
Focus:
Grids have a focus, a length between the grid and X-ray tube in which they work the best. If you have the wrong focus, the sides of the image will be dark and you will see much thicker grid lines. Focuses are written in a range (ie, 40-72”), but what that really means it is focused in the center of that ranged and at the edges are “OK”. That’s why high end facilities will buy two grids and swap them instead of one 40-72” grid.
Not All Grids are the Same #2
Line Pairs/Frequency:
All grids have a frequency, expressed in Line Pairs/cm or Line Pairs/in. This is how many pairs of 1 lead strip and 1 interspacer there are in a cm or inch. With DR systems, this is extremely important.
The standard for film has always been 103lpi, though lower were also used. This wasn’t a problem because with film, you can move (“reciprocate”) the grid so the lines are blurred across the film. You can’t do that with DR because it can cause strange artifacts.
There are two solutions for Digital Radiography (DR):
- Use a 103lpi grid and remove the lines with software. This option is about $1,000 cheaper.
- Use a high line (215lpi or 230lpi) grid. The lines are so small they cannot be seen by the detector. This gives the best image.
Since line frequency really wasn’t important with film, a lot of older grids have poor quality control. Many of our less expensive competitors are still only within 10% or even more of their stated specification. This can be the source of image quality issues.
We have provided links to additional JPI grid content below:
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