For example, less scatter is produced in bone than in soft tissue, because bone absorbs more photons photoelectrically.

The greater the atomic number of the tissue, the less will be the quantity of scatter created. (Therefore, scatter increases and contrast is further impaired as kVp increases.) An important point to remember is that the percentage of Compton interactions increases with increased kVp. Scattered photons add an overall exposure to the image receptor and, as a result of this overall graying of the image, contrast is lowered. These differences exist because some photons pass through the body while others are absorbed. These are the photons responsible for creating the contrast (differences in the image receptor exposures or densities) on the image. The photons that pass through the body unaffected will interact with the image receptor to create the image. They will (1) pass through the body unaffected, (2) be absorbed by the body, or (3) interact and change direction

When an x-ray beam passes through the body, one of three things will occur with the primary photons that originated at the target. A grid is a device used to improve the contrast of the radiographic image.) It does this by absorbing scatter radiation before it can reach the image receptor.

Two types of grids in radiology