Introduction to X-Rays Flashcards
Who discovered x-rays?
Wilhelm Röntgen (1895)
Who made the first dental radiographs?
Frank Harrison - Dentist
What is an x-ray?
An X-ray is a quick, painless test that produces images of the structures inside your body - particularly bones. X-ray beams pass through your body, and they are absorbed in different amounts depending on the density of the material they pass through.
What is a photon?
A photon, also called light quantum, minute energy packet of electromagnetic radiation.
What happens when a HIGH energy photon hits the patient?
Passes through the patient (scattered)
What happens when a LOW energy photon hits the patient?
Stops inside the patient (absorbed)
Name the three types of radioactive emissions:
- Alpha particles
- Beta particles
- Gamma rays
Name the 7 types of radiation, in order from the lowest photon energy to the highest photon energy (the electromagnetic spectrum)
Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, Gamma waves
What types of radiation are IONISING?
X-rays, Gamma rays, and SOME UV rays
What is an atom comprised of?
Protons (+), Neutrons (no charge), Electrons (-)
Define: ‘atomic mass number’
The sum of the number of protons, and neutrons in an atomic nucleus.
What is an isotope?
Atoms with the same atomic number but with different atomic mass numbers - they have differing numbers of neutrons.
Define: ‘ionisation’
The process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes.
What is the cathode?
The cathode (-) is part of an x-ray tube that heats and expels the electrons from the circuit and focus them in a beam on the focal spot of the anode.
What is the anode?
The anode (+) is a small target (usually tungsten and copper) that receives the electron beam from the cathode and emits it as X-ray.
What is kVp?
Kilovoltage peak (kVp) is the peak potential applied to the x-ray tube, which accelerates electrons from the cathode to the anode in radiography or computed tomography. Tube voltage, in turn, determines the quantity and quality of the photons generated.
What is mA?
Milliampere. Changing the mA affects the QUANTITY of x rays produced. Increasing the mA setting increases the current in the circuit by increasing the temperature of the filament (cathode). The hotter the cathode, the more electrons that are emitted, and the MORE x-rays that are produced.
In dental radiography, the quality of the x-ray beam is controlled by which setting?
kVp (tube potential)
What is the standard kilovoltage range for most dental x-rays?
65-90 (100)kV
A unit of measure used to describe the number of electrons passing through a conductor
Ampere
Increasing milliamperage results in an increase in ______?
Temperature of the filament, and the number of x-rays produced
What is the milliamperage range for dental radiography?
7-15mA
What are the FOUR main types of x-ray interactions?
- Photon completely scattered with no change of energy
- Photon totally absorbed
- Photon scattered after some loss of energy
- Photon transmitted unchanged
What is the photoelectric effect?
Occurs when a photon collides with an INNER shell electron in the patients tissue. All of the photon energy is absorbed, and the atom is de-stabilised. When the atom re-stabilises, it gives off heat and light
What is the Compton effect?
Occurs when a photon collides with an OUTER shell electron in the patients tissue. The electron loses only some of it’s energy, and is deflected.
Name the four ways that xray photons interact with matter
- Transmission: they pass straight through without touching anything
- Absorption: they hit the matter and all their energy is absorbed
- Absorption and Scatter: they hit the matter and are deflected in another direction with a loss of energy
- Pure scatter: they are deflected in another direction with no loss of energy
Can xrays travel in a vacuum?
Yes
Do xrays travel in straight lines?
Yes
Do xrays have a short wavelength or a long wavelength?
Short
Are xrays high energy or low energy?
High energy
What is the high voltage push?
The speed at which the electrons are accelerated from the filament towards the tungsten target. This determines the overall energy of the xray photons (kV)
This essentially controls the penetrating power, and therefore the QUALITY of the beam.
Which are more damaging to the patient, high energy photons or low energy photons?
Low energy - They are absorbed by the tissues and are not able to penetrate the tissues to be absorbed by the xray film instead
What is the operating range of dental xray equipment?
60-70kV
How thick is the aluminium filter?
1.5mm thick for <70kV
2.5mm thick for >70kV
Should the xray machine run on AC or DC?
DC - constant potential
What is the maximum recommended diameter for circular collimators?
60mm
What is the recommended FSD?
200mm or long spacer cone
300mm for more modern sets
What would happen if you increase the kV?
Decreases the contrast of the film
‘kV kills contrast’
(kV controls quality of the xray photons and their penetrating ability)
What would happen if you increase the mA?
Increases the degree of blackening of the film
(mA controls the quantity of the xray photons produced)
