How to Reduce Diffraction Scatter in Radiography

Radiographs, commonly called x-rays, are images produced when a beam of radiation passes through the patient's body to a detector. Frequently, a few of the photons that make up the x-ray beam encounter obstacles along their path and scatter from the primary beam, causing the resulting image quality to suffer. Collimation, air gaps and grids are techniques radiologists use to minimize this diffraction scatter.

Collimation

In radiography, the larger the area included in the x-ray, the more scatter you get in the image. Collimation means reducing the field size of the x-ray beam to the smallest possible area in order to produce a better image. For example, if you needed to visualize the elbow joint on a film, you would narrow the beam to focus on the joint and a small portion of the structures above and below it. You would not include the whole arm and shoulder in your film unless you had a very good clinical reason to do so. Limiting the area of focus minimizes scatter and allows you to produce better image quality.

Use of Grids

A grid alternates strips of x-ray absorbing and non absorbing material aligned with the x-ray beam. The idea behind this is that the absorbing material should absorb most of the scatter, while the non absorbing material allows the primary beam to pass through to the cassette which records the image. Because scatter is more severe when the x-ray beam needs to penetrate a thicker area, many radiologists recommend using grids when the body part to be imaged is thicker than 10 centimeters.

Air Gap

When an x-ray beam passes through the body, scattered radiation spreads out faster than the primary x-ray beam. Leaving a space between the patient and the detector that captures the image can prevent a significant amount of scattered radiation from corrupting the final image. This technique is limited because it magnifies the image, and it increases the radiation exposure to the patient.