Dental Radiography Flashcards
What is the definition of Radiography?
Uses x-rays to produce images.
What is the definition of Radiology?
The use of images to diagnose and treat disease..
What does EMR waves stand for?
Electromagnetic Radiation.
what is the definition of EMR?
- Use energy and momentum
- Electric and magnetic
- Travel at 90 degrees to each other
- Wave packets (Photon/Quantum
- No mass
- Measured in electron Volts (eV)
- Can travel through a vacuum
- Vibrates transferring energy from one place to another without matter being transferred
- some waves require a medium to travel through eg sound waves
What is a photon?
A wave/ energy packet and can be both wave and particle and should the frequency be doubled then the energy of the photon is doubled.
what is frequency?
- number of repetitions in a given time period
- Greek symbol is Nu or V
- more repetitions the higher the frequency but a shorter wave length
- measured in hertz HZ
The shorter a wave length…….?
the more dangerous they are
Cancer can be caused by……?
Any waves shorter than visible light eg Gamma rays are the shortest then xrays!
What is Ionising radiation?
- It carries more energy than non- ionising radiation
- can create charged ions by displacing electrons in atoms
- radiation from radioactive sources and naturally occurring radiation.
What is Ionising radiation used for?
used in medicine - Diagnostically, caries in teeth
-Therapeutic, treatment in cancer
What is Non-Ionising Radiation?
Changed position of atoms but does not change or alter the make up, structure or properties
Are dental xrays safe?
the risk of biological damage is small but there is still a risk
In the UK how many xrays are taken in a year?
approximately 20-25 million intra and extra oral a year
In the UK how many fatalities per year?
Approximately 10 fatalities per year
All exposures must be kept…..?
ALARP as low as reasonably practical
Name X-ray equipment…?
- Tube head
- positioning arm
- control panel
All x-ray equipment must be….?
- safe and robust
- accurate and simple to operate
- must produce suitable x-rays, both film and digitak
- small
- easy to position, move and store
- stable and balances when positioned
- outer casing made of lead and checked daily for damages
- x-ray tube in glass envelope which is filled with oil to remove heat
- step up transformer which increases the voltage from 240V to 60-90 kV
- step down transformer which decreases 240V to 7-10V required to heat the filament
- Spacer cone/beam indicating device
- Collimator
- Aluminium filtration removes harmful low energy x-rays (Soft xrays less than 30KeV)
- Focal spot
What happens at the glass envelope inside the xray tube?
located at the back of the tube head, completed surrounded by lead which absorbs unwanted x-rays which are travelling in all directions which creates a vacuum.
What is a cathode?
-made up of a tungsten filament which is centred in a focusing cup
-electrons are produced by the filament and focused onto the target on the anode
-Focussing cup has a negative charge ( same as electrons) and helps direct to target
-
What is Thermionic Emission?
- when the exposure button is pressed the electricity flows from the filament in the cathode and the filament gets hot
- the hot filament then releases electrons which surround the filament
- the hotter the filament gets the greater number of electrons released
What is the anode?
- comprised of a tungsten target on copper base
- when the electrons from the filament hit the target and generate the xrays, heat is produced
- the copper target helps take the heat away as it could get to hot
What is the focussing cup?
Aims the stream of electrons to the focal spot on the target
What is the focal point to skin distance?
- Not less than 200mm for kV under 60kV
- Not less than 100mm for kV over 60kV
Older pointed xray machines must not be used why?
They produce scatter on x-rays
Blurring of image is called…?
the penumbra effect
The collimator should be….?
-rectangular with a maximum diameter of 40mm X 50mm, this will ensure that the maximum overlap when using an intraoral film size 2 is 2mm
what is Filtration….?
-reduces skin dose
-removes non diagnostic/low energy xrays/soft radiation (which is more readily absorbed by patient hence why so damaging
-thickness must be 1.5mm below 70kV
and
2.5mm above 70kV
Control Panel must include….?
-mains on/off switch with warning light
-Timer electronic impulse or clockwork
Exposure time selector, numerical/ anatomical (picture of teeth)
-exposure warning light with audible signal
May also include
- film speed selector
-patient size selector
-mains voltage compensator
-kilovoltage selector
- Miliamperage switch
-exposure adjustment for digital imaging
What is the alternating current in relation to radiography?
- Measured in Voltage (V)
- half is negative, half is positive current
- only positive is needed for production of xrays
- A step up of voltage is needed to eliminate negative
- equipment is working at peak output at top of cycle measured in kVpeak or kvP
Direct Current is used by modern xray machines
- keeps the kV at kVpeak throughout all exposure
- xray production per unit time is more efficient
- more high diagnostically useful photons are produced per exposure
- few lower energy photons are produced
- shorter exposure time
what factors affect the intensity of the beam?
- size of the tube voltage kV
- size of tube current mA
- distance from target d
- time = length of exposure
- filtration
- target material
- tube v waveform
in free space xrays travel in straight lines and obey then inverse square law which means?
-Intensity=I/d2 which means it decreses the further away it gets from the beam
shorter wave lengths=
greater energy and can therefore penetrate a greater distance
longer wave lengths=
low energy and have little penetrating power. (soft energy)
Xrays are referred to as….?
Ionising radiation
xrays can affect film emulsion….?
to produce a visual image and can cause certain salts of flourescence
In a year approximately how many dental xrays are taken per year?
20-25 million
How many fatal malignancies a year?
10
What is a step up transformer?
Step up transformer – increase the voltage from 240V to 60-90kv
What is a step down transformer?
Step down transformer – decreases the 240v to 7-10v required
Aluminium Filtration reduces skin dose….
- 5mm below 70kV
2. 5mm above 70 kV
