INTERACTION OF X-RAYS WITH MATTER
X-rays are a form of ionizing radiation. They interact with atoms and knock electrons off the atom to create an ion which is an electrically charged atom. Free electrons then collide with other atoms to create more ions. An ions' electrical charge can lead to unnatural chemical reactions inside the cells and it can also break DNA chains. A cell with a broken strand of DNA will either die or develop a mutation if the cell is unable to repair the damage. If a lot of the cells die, the body can develop various diseases. If the DNA mutates, a cell may become cancerous and this cancer may spread to the detriment of the host. If the mutation is in a sperm or egg cell, it may lead to a birth defect or to affect future generations.
When an object is exposed to a beam of radiation, it absorbs and transmits resultant radiation after interaction with the various densities (radiation absorbing properties) within the object. The transmitted radiation carries with it the information of the structures after it's attenuation.
ATTENUATION: the reduction in the number of primary photons in the x-ray beam through
scatter: change in direction of travel that may also involve a partial loss of radiation energy
direct transmission: photons that traverse the object without interacting
indirect transmission: primary photons Compton and/or coherent interactions and may be scattered or deflected
There are 5 types of interaction between x-radiation and matter are possible:
← Coherent scattering
← Compton scatter
← Photoelectric absorption
← Pair production
Only two are important in diagnostic radiology:
Image formation is dependent on the formation and control of scatter, the photoelectric absorption and the direct transmission of the primary beam incident on a patient.