Radiology Flashcards
What are X-rays
- Form of high energy electromagnetic radiation
- Short wavelength
- Packets of energy made of photons
What are the components of x ray tube
- Cathode: emits electron, typically made of tungsten
- Anode: bombarded with electron cos its positive, copper or tungsten
- vacuum
What are the two types of x-ray collisions
- Continuous spectrum
- Characteristic spectrum
- Other is heat producing collisions
What is the continuous spectrum
- High energy electron goes close to the nucleus
- Changes direction and loose energy
- X ray is released
What is characteristic spectrum
- Knock electron out of the inner shell
- Outer shell electron fills vacancy
- Releases an x-ray
What is critical voltage
- Minimum energy needed for x ray
- Tungsten 69.6 KV
What is radiation absorbed dose
- Amount of energy absorbed from radiation beam
- Measured in milligray (mGy)
What is equivalent dose (Ht)
- Equivalent dose = radiation absorbed dose x radiation weighting factor (Wr) for particular tissue
- For individual organs
- Measured in sievert (Sv)
- Wr for x ray is 1
What is tissue weighting factor
- More risk of damage the higher the Wt
Name some bodies
- ICRP (international commission on radiological protection)
- IR (ME) R (ionising radiation medical exposure regulation)(2000-2018)
- IRR (ionising radiation regulations)(1999 -> 2017)
What are the changes in IR (ME) R
- Employer insure individual patient aware of risk and benefit
- Employer collect dose estimates from medical exposures
What is IR(ME)R consist of (protects patient)
- Referrer (justify)
- Practitioner (take responsibility)
- Operator (exposure and process)
- Employer (ultimate responsibility)
What are the changes of IRR
- How to tell health safety exec you work with IR
- Reduced does limit for lens of eye from 150 to 20msv
What does the ICRP say
- Prevent deterministic and limit stochastic
- Justification: benefit outweigh the risk
- Optimization: ALARP (as low as reasonably practicable)
- Limitation: patients, radiation workers, general public (does should not exceed limits)
What is the panoramic dose
- 16-26 microsivert (includes the salivary glands)
- 7-14 microsivert (without salivary glands)
- 2.7 (maybe)
Whats the does for intra oral film
- 0.3-21.6 micro sivert
- 0.3 (maybe)
Whats the maximum does
- 20 milisivert
What is somatic deterministic effects
- Directly related to radiation received
- Dental radiation quite low so low risk of this
- Cataract, loosing fingers
What is somatic stochastic
- Not directly related to radiation dose
- Random
- Malignancy
How do x-rays cause damage
- Direct damage (hitting DNA)
- Indirect damage (water ionises and then damages DNA)
What are the dose reduction techniques divided into?
- Equipment
- Clinical decision
- Practical technique
- Diagnostic interruption
Tell me how to limit radiation from equipment
- Aluminium filtration (remove low energy photons)
- Collimator (minimise scatter radiation)
- Beam indicator device (correct distance and direction)
- Lead
- Kv,mA,time
What happens to changing Kv
- Higher Kv lighter (also more penetrating)
- 70Kv
- Increasing kv more dose
What happens when you change mA
- Increasing mA
- Makes it darker
Tell me how clinical decision reduces does
- Justification
- Evidence based selection criteria
What is the controlled area
- 1.5m from the tube
- Radioation protection advisor (RPA)
- Design of the x ray room or controlled area
What to do in malfunction
- IRR (equipment malfunction) (HSE)
- IRMER (clinical error)(IRMER )
What are the local rules
- RPS
- RPA
- Controlled areas
- Personal dosimetry
- Pregnant staff
What are the types of radiography
- Digital (direct and indirect)(Solid state sensor vs PSP)
- Conventional (manual, automatic)
What does conventional film consist of
- Cover
- Film (silver halide)
- Lead
How does silver halide work
- Developer (green silver halide converted to black)
- Fixer (black metallic fixed to plastic base)
- Wash ( washes off fixer )
- Unexposed silver not effected by developer and removed by fixer
What are film processing errors
- Concertraion of chemicals
- Development time
- Temperature of chemical
- Handling
What is PPP
- Patient preparation
- Patient positioning
- Radiation exposure
- Image processing
What are the two techniques taking a PA
- Paralleling technique
- Bisecting angle
Name some x ray errors you can see
- Overlapping (horizontal plane error)
- Elongation/ foreshortening (vertical plane error)
Angle for upper standard occlusal
- 60-70 degrees
- Cant tolerate PA
- Pathology
- Unerupted teeth parallax
Lower standard occlusal
- Lower 90 degrees (true occlusal)
- Lower 45 degree
- Salivary gland, pathology, cysts
How to position the head
- Laser to align the patient (canine light)
- Should me straight
What angle is the opg
- 5-6 degrees to stop superimposition of the hard palate
