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Grid ratio and cleanup
Higher grid ratio cleans up more scatter but costs dose and tolerates less misalignment.
The rule
A grid is a series of thin lead strips separated by radiolucent interspace material, placed between the patient and the receptor. It absorbs scatter before it reaches the receptor, which improves contrast. Grid ratio is the height of the lead strips divided by the distance between them, so taller strips or narrower gaps mean a higher ratio. Common ratios run from 5:1 to 16:1. A grid is generally used when the part is thicker than 10 cm and the technique is above 60 kVp.