Cross Grid

Two parallel or focused grids of half the thickness and ratio are assembled into one cross grid.
The scatter absorption of a cross grid is approximately the same as that of a one component grid of the same ratio. However, the 2-directional absorption of a cross grid absorbs more scatter originating from the interior of the object than with a conventional grid of the same ratio. A cross grid is suitable, where a grid with very high ratio is required.
Cross grids are advantageous, when deviating from a right angle arrangement of the film plane, since the cross grid only has half the ratio of the linear grid but in two directions.

High kV Technique

At kilo voltages above 125 kV, the scatter radiation increases significantly and necessitates the use of the most efficient grid. Primary absorption in the grid is of little importance. A grid of high ratio and high number of lines to the cm should therefore be selected despite of the difficulty of correct alignment. Optimum quality is achieved by the use of high definition intensifying screens and a relatively long focal-film distance. In order to minimize geometrical unsharpness, LYSHOLM focused grid: N70, r 12 or r16 are recommended.

For a more deep going analyse the document "A guide to the proper use of Lysholm scatter radiation grids" is available as a PDF document.
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