Radiology Flashcards
what is a radiograph?
image created by different absorption of x-ray photons by different tissues.
anatomy = what is the white Y shape structure found above upper 1-4?
Y shape of Ennis.
what is an xray beam a stream of?
photons
what is an electron volt?
electron accelerated through an electric field with a potential difference (voltage) of 1V gains 1eV in energy.
what are the 2 mechanisms of x-ray production?
- Bremsstrahlung (electron-nucleus interaction)
- Characteristic spectrum (electron-electron interaction)
How does Bremsstrahlung produce xrays?
with a range of engeries determined by the tube potential
How does Characteristic produce xrays?
with just afew discrete energies determined by the target material.
what are the x-ray tube components?
- Cathode
- Anode
- Filter
- Cooling oil
- Shield
- Evacuated glass tube
- Shielded metal housing
- Window
- Oil.
what is the purpose of the evacuated glass tube in the xray tube?
to get to target.
prevents xray protons going in all directions.
what is the purpose of oil in the x-ray tube?
removes heat.
What is meant by Tube Voltage (kV)?
electron energy is proportional to the potential (voltage) between anode + cathode.
what is meant by Tube Potential (kVp)?
affects both the quantity of x-rays produced and the shape of the x-ray spectrum (quality)
what is meant by Tube current (mA)?
the electrons flowing from cathode to anode form an electron current which is measured in mA. Total quantity of xrays is determined by the current (mA) and the tine for which it flows (s)
what is the intensity of x-rays proportional to?
tube current
what does the tube current and exposure time only affect?
the quantity of the x-rays
what does filtration affect?
the quality and quantity of the xrays
how does filtration increase the beam energy?
preferentially removes lower energy xrays
for a standard diagnostic x-ray tube, what should the filtration be at?
at least 2.5mmAl.
should the focal spot of xrays be large or small?
small
what would result if the focal spot of an xray is too small?
xray tube overheats.
why does there need to be heat removal in the xray tube?
- prevent damage to focal spot and target
- to prevent general overheating of the tube.
what structures in the mouth will absorb the most protons?
bones and teeth.
what is attenuation of xrays?
the total process of reducing the intensity of an xray bea,
How can attenuation be achieved to produce good contrast in an xray?
photoelectric absorption - photon energy transferred to electron.
How can attenuation be achieved to reduce contrast in an xray?
compton scatter - photon energy partially transferred to electron
what does xray energy need to be high enough to do?
traverse the tissue thickness of interest and minimise scatter.
what does xray energy need to be low enough for?
to be altenvated in the appropriate tissue.
What type of xrays can be used to gain a 3D image?
CT scans and MRI
How can you change contrast of an X-ray image?
Change the quality of the radiation (but this could increase scatter, to reduce this reduce kV, change pt orientation, compression, anti-scatter grids, air gap and reduce field size)
What are factors that affect X-ray image unsharpness?
- receptor
- geometric
- movement
How can you prevent noise in an X-ray image?
Increase the number of X-ray photons forming the image
What is noise when talking about an X-ray image?
To many photons to one area - so can no longer detect contrast differences
What is ionising radiation?
High radiation
What are the harmful effects of radiation?
- cancer
- cataracts
- skin darkening/ burns
- hair loss
- sterility
What are some beneficial effects of using radiation?
- Saves lives via radiotherapy
- early diagnosis
- sterilisation of blood products/ food stuff / dressings
What are the 3 ways in which xrays interact with tissues?
- Transmitted
- Scattered
- Absorbed
What is the purpose of transmitted xrays?
Help us to form the image we want to see
What is mean by scattered xrays?
Xrays that can be absorbed by others in the room that it wasn’t meant for
What is meant by absorbed xrays?
Absorbed xrays that deliver a radiation dose to the patient and can potentially cause harm
What are your bodies cells most at risk from damage from xrays?
During the replication stage - G2 and mitosis.
What type of cells in the body are most sensitive to damage from xrays?
Active cells - WBC and bone marrow.
What are the effects that the xrays can have on the cells in the body?
Xrays can cause ionisation of the cellular water leading to changes molecularly and the formation of chemicals that can damage chromosomes. This changes the structure and function of the cell.
What are the Effects on the body of X-ray damage dependent on?
Dose, dose rate, area irradiated and sensitivity of organs/individual
What type of radiation effects can happen in dental X-rays (but is very unlikely) ?
Stochastic
What is a stochastic effect?
Chronic, potential long term effect.
Occurs randomly but probability of effect depends on dose.
Can cause cancers, harm to future generations due too harm to reproductive organs
What are the ICRP principles for protection again radiation?
- Limitation
- Justification
- Optimisation