X-Ray Flashcards
Basics of X-ray
X-rays are a form of electromagnetic radiation, like visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body. If x-rays travelling through the body also pass through an x-ray detector on the other side of the patient, an image will be formed that represents the “shadows” formed by the objects inside the body.
How do X-rays work?
To create a radiograph, a patient is positioned so that the part of the body being imaged is located between an x-ray source and an x-ray detector. When the machine is turned on, x-rays travel through the body and are absorbed in different amounts by different tissues, depending on the radiological density of the tissues they pass through. Radiological density is determined by both the density and the atomic number (the number of protons in an atom’s nucleus) of the materials being imaged.
How do X-Rays show bone?
Structures such as bone contain calcium, which has a higher atomic number than most tissues. Because of this property, bones readily absorb x-rays and, thus, produce high contrast on the x-ray detector. Thus, bony structures appear whiter than other tissues against the black background of a radiograph.
Attenuation Coefficient
The attenuation coefficient is quantified as the measure of how easily a material can be penetrated by an x-ray beam. It quantifies how much the beam is “attenuated” (i.e. weakened) by the material it is passing through.
Compton scattering
The is the scattering of photons, by coming into contact with charged particles.
Compton scattering results in a decrease in the energy of the photons and reduces the resolution of the images.
One thing to consider is the signal-to-noise ratio. ideally, a ratio of 2:1 is needed. With Compton scattering, the noise of the image would increase, and therefore reduce the SNR and give rise to an image of reduced quality.
Risks
X-rays produce ionizing radiation—a form of radiation that has the potential to harm living tissue. This is a risk that increases with the number of exposures added up over the life of the individual. However, the risk of developing cancer from radiation exposure is generally small.
An x-ray in a pregnant woman poses no known risks to the baby if the area of the body being imaged isn’t the abdomen or pelvis. In general, if imaging of the abdomen and pelvis is needed, doctors prefer to use exams that do not use radiation, such as MRI or ultrasound.
