Principles of Radiography Flashcards
What is an X-ray?
A form of non-particulate radiation
What is a radiograph?
A radiograph is a shadow of an object placed in the x-ray beam. Radiograph images have contrast as x-rays are more penetrating than visible light.
What is the relationship between the energy of radiation and its wavelength?
The higher the energy the lower the wavelength.
How is an x-ray produced and what is needed to produce them?
X-rays are produced when electrons collide with atoms of heavy metals e.g. tungsten. Therefore one needs a source of electrons, a method of accelerating them and a target.
Label the diagram
a=tungsten
b=copper (conducts heat away from tungsten)
c=cupped end of filament to concentrate electrons
d=filament
e=vacuum
What is the purpose of the voltage across the x-ray tube and what voltages are there?
Low -ve voltage on the filament and high +ve voltage on the tungsten end. The voltage attracts electrons that have the energy to cross the gap.
What does x-ray absorption depend on?
Tissue density, atomic number and thickness. As all of these increase the no. of electrons in the path of the x-rays.
Describe the opacity of tissues that can be visualised by radiography from lucent to opaque.
air, fat (e.g.between organs), water (soft tissue), bone, metal
What are the different forms of contrast media?
Positive = contains a radio-opaque material. Has high atomic numer.
Negative = air
‘Double’ = use of both of the above
What are the different controls on the x-ray machine?
kVp = kilavoltage peak - energy of electrons
mA = current - number of electrons
sec = time the current is applied for (no. of electrons)
What is Bremsstrahlung radiation and how does it work?
X-rays produce by the change in KE of electrons which pass through the tungsten atom. The energy of the electrons produced is dependent on the distance they pass by the nucleus so a broad spectrum of x-ray energies is produced.
What is the purpose of the aluminium filter?
To prevent low energy x-rays from hitting the patient.
Compare the changes that would be seen by altering mAs and kVp.
kVp = more x-rays and higher energy
mAs = more x-rays with same median energy
therefore changing kVp to increase exposure is better as it means the same exposure can be reached without excessive x-ray doses to the patient.
What needs to be altered as the patient gets thicker?
kVp will need to be increased (as altering mAs would still not result in high enough energy x-rays)
