Anti-scatter grids
Top: a magnified cross-section of a grid showing thin lead strips of height h separated by wider interspaces of width D, with grid ratio defined as h divided by D. A vertical primary ray passes through an interspace and reaches the image receptor, while an oblique scattered ray is absorbed by a lead strip. Bottom left: a focused grid at the correct focal distance, with lead strips angled to converge on the focal spot so primary rays run parallel to the strips and are transmitted. Bottom right: with the tube off-centre or at the wrong distance the rays no longer match the strip angulation, so peripheral rays strike the lead and are absorbed, producing grid cut-off with reduced density at the edge.
Practice the Physics paper
FRCRX is a Part 1 Physics question bank: true/false items with explanations, timed mocks and topic analytics.