Ionising Radiation

Abstract

X-ray photons directed at a patient do one of these three things:

• 1. Are passed straight through the patient (who is mostly empty space) without deviating from their trajectory, to strike the detector and form the medical image.

• 2. Are stopped within the patient by ionising some of the patient’s atoms, leaving their energy in the patient’s tissues. This absorbed energy contributes to the patient’s “absorbed dose” of radiation.

• 3. Or are deflected from their path so they do not reach the detector. These “scattered” photons don’t contribute to the image. They may increase the radiation dose to the patient and will irradiate people nearby. Hence radiographers wear protective “lead” aprons which absorb this (relatively low-energy) scattered x-radiation.