Radiology Flashcards
How many bananas is equivalent to 1 x-ray. and how long a flight
50 bananas, 4 hour flight
How x-ray can cause cancer
-Indirect= ionising water - Due to their high energy they can remove an electron from an atom it collides with and create a free radical. Free radicals steal energy from other molecules causing damage
-Direct= ionising biological molecules DNA is damaged which can mutate and cause cancerous cells
Distance of focal spot to skin surface of patient. Distance between operator and X-ray tube (controlled area)
20cm
1.5m radius, or in direct beam. 1m for PAs
What causes light and dark x-ray film
Dark= over exposure, overdeveloped
Light= under exposure
The 3 planes that need to be checked when taking a DPT
Mid sagittal
Alar tragal
Focal trough (between 2 and 3. or side of nostril)
Where is the pip located for a PA and a bitewing
-PA: Pip down to crown
-Bitewing: pip upwards to palate
Exposure time for bitewings. And the kV and mA settings
-anterior= 0.2s
-posterior=0.25s
66kV, 8mA
In the X-ray tube, what % is heat and what is x-ray
1% x-rays
99% heat
What are the 5 principles of shadow casting (what is required for a good quality image. Do you want distance between object, source, film to be small)
- Radiation source as small as possible
- Source to object distance large
- Object to film small
- Object and film parallel
- x-ray beam perpendicular to object and film
Definition of resolution and sharpness
how well the details/ boundaries/ edges are reproduced
What 5 things can cause unsharp images
- Movement of patient
- Distance of object to source
- Distance of object to film
- High F speed (required to reduce radiation) causes unsharpness
- Pixel size
For a sharp image, do you want a large/ small distance between i) source to object. ii) object to film
I) large. Penumbra is smaller. Less magnification as beam less divergent (think of a projector and white board and casting a shadow)
ii) small
What is i) cervical burnout ii) overlapping. the causes
I) radiolucent band around necks of teeth due to higher penetration of the beam as this is the thinnest part
ii) no inter proximal areas due to poor horizontal angulation.
what does the kilovotlage refer to. What does a lower value mean. What value is usually used, and what is used for soft tissues
-70 used, 60 used for soft tissues
-it is the difference in potential applied to the X-ray tube. Adjusts the penetration and exposure and contrast
-beam quality
-lower= increased contrast
-higher= gets through patient quicker to reduce exposure time. darker film
what does the current refer to
beam quantity
intensity fo photons exiting the tube
The steps in x-ray production in the tube. the different components
X-ray tube is a vacuum that converts electronic power into x-rays
-a transformer increases the voltage from the mains, to 40-90kV
-oil is used for cooling
-at the cathode, the wire is super heated so electrons form a cloud
-electrons accelerated by potential difference and attracted to positive anode
-electrons hit at higher energy and release x-rays as they slow down
-hotter means more electrons, more x-rays, higher intensity
What happens to the radiation dose every time you double your distance away from the source
radiation quarters
what is scatter and how it affects the film
sometimes only a portion of a photons energy is transferred to the matter and can deflect off the matter. Can contaminate the film with fog. Can be minimised using collimators and aiming devices
What is the photoelectric effect
-the effect increases with atomic number
-incoming photon hits electron in an atom and transfers its energy to it
-electron knocked out
-atom becomes unstable
-valancy filled by electron from higher shell
-energy released in the form of light
What is the Compton scattering effect
-increases with increased kV
-incoming photon hits electron in atom
-photon and Electron both deflect in different directions
-this adds to the patients dose. Photons will scatter many times, losing energy each time
What chemical is on the film and how it works
x-ray hits silver bromide crystals on film. Become sensitised and unstable. Electrons attracted. Silver ions reduced to become black metallic silver atoms.
-highly dense amalgam, means x-rays poorly penetrate as they are absorbed so do not hit film and it appears white
-less dense soft tissue means more penetration and appears blacker
How Many micro SV is a full DPT
19
