All the lead strips cut off the same amount of primary radiation Most common type of grid cut off but cannot be recognised by inspection of the film.
When a crossed grid is used upside down, only a small square in the center of the film is exposed. THE FOCUS OF the lead strips is called the tube side and all focused grids have it.The final image with be light in the area in which cut off occurs. Primary disad-increase the amount of radiation a person receives and the careful centering of the xray tube because of the danger of grid cut off.The amount of Lead is a good indicator to improve contrast provided the grid is well designed.
Its weight in grams Is the lead content of the grid. Imagine cutting up a grid into I cm squares and then weighing them. High ratio grids absorb more scatter radiation and have larger bucky factors than low ratio grids.
Grids are used to improve contrast by absorbing secondary radiation before it reaches the film.I ll b talking about Lead content in the upcoming slides.A grid with many lines per inch is gfenerally thinner and has a lower lead content than a grid of comparable ratio with fewer liner per inch. The grid ratio, lines per inch and the lead content are closely related.Focusing range is fairly wide for a low ratio grid and narrow for a high ratio grid. In practise grids have a focusing range that indicates the distance within which the grid can be used without significant loss of primary radiation. May be either linear or crossed because the focussing refers to the cross sectional plane.Higher the grid ratio, better the grid functions. Grid ratio is a parameter widely used to describe a grids ability to remove scatter radiation. 1 Is usually a constant and the first number being the actual value. Grid ratios are usually expressed as two numbers such as 10:1 or 5:1.Patient exposures are higher with aluminium because it absorbes more primary radiation. Aluminium grids are structurally stronger than grids with organic interspacers. Main purpose of the interspace material is to support the thin lead foil strips. so most of it is absorbed by Lead strips and only a small amount passes between them. Scatter radiation is multidirectional and arises from many poinbts within the patient.