Radiology Flashcards
What does the black paper in direct action film do?
Protects from light
Stiffens/supports
What does the foil in direct action film do?
Composed of lead and aluminium to absorb x-rays and prevent back scatter
Pattern so if film placed wrong way round will know
Describe the layers of the film in direct action film
Plastic base
Adhesive layer
Emulsion
Supercoat- Protective layer of gelatine
What does the plastic base of direct action film do?
Supports emulsion
What does the adhesive in direct action film do?
Fixes the emulsion to base
What does the emulsion in direct action films contain?
Silver halide crystals embedded in gelatin matrix
What reaction occurs in the emulsion layer?
The x-ray photons sensitise the silver halide crystals which are then later reduced to black metallic silver during the development process
What does the protective layer of gelatine in direct action film do?
Shields the emulsion
What side should the dot be placed, towards or away from the x-ray beam?
Towards the x-ray beam
Indirect action film is used in conjunction with what?
Intensifying screens in a cassette
Name the layers of indirect action film
Cassette front Sponge rubber Front intensifying screen Emulsion Back intensifying screen Sponge rubber Cassette back
What could cause extreme blackening of an image?
Light
How is ALARP achieved?
IRR 1999 (appropriate equipment well maintained) IRR 200 (only take radiograph if clinically necessary) Rectangular collimation Use fast film to reduce dose Lead protection (thyroid collars)
What kind of patient is more sensitive to X-rays?
Young patient
Where is the radiographic base line from?
Outer canthus of eye to EAM
Where is the frankfort plane from?
Inferior orbital border to upper border of EAM
Where is the maxillary occlusal plane from?
Ala of nose to triages of ear
What are the layers of phosphor plates?
Protective layer
Phosphor layer
Reflective layer
Backing layer
What are the layers of CCD?
Back cover
Silicon wafer
Scintillator layer
Front cover
What are the layers of phosphor plates?
Protective layer
Phosphor layer
Reflective layer
Backing layer
What are the differences between phosphor plate and CCD?
Phosphor plates have a phosphor coating on plates which absorb x-rays and are scanned to release energy as light whereas solid state is similar to image capture in a digital camera
What are the advantages of phosphor plate?
Can be used with existing film holders
Tolerated well by patients
What are the disadvantages of phosphor plate?
Plates easily damaged
Relatively expensive
Sensitive to background radiation
What are the disadvantages of CCD?
Can only be used with its own holders
Not tolerated well by patients- can be bulky
Sensors very expensive
Easily damaged
What does the practitioner do?
Justifies the exposure
How does characteristic radiation work?
Incoming electron collides with an inner shell electron and either displaces it into a more peripheral shell (excitation) or removes it completely (ionisation)
How does continuous radiation work?
Incoming electron passes close to target nucleus, causing it to be rapidly slowed down and deflected and produces bremsstrahlung x-ray photons
How would you do an occipito mental radiograph?
Radiographic base line of 45 degrees to film, angle beam 10 or 30 degrees to feet, aim centre of beam through midline of patient and through base on nose
What are the contents of a film packet?
The outer wrapper
The film
The sheet of lead foil
The protective black paper
What does the high voltage between the cathode and the anode do?
Accelerates
What does the high voltage between the cathode and the anode do?
Accelerates the e- from the negative filament to the positive target. Sometimes referred as a kilovoltage peak
What is the measure for the quantity of e- being accelerated?
Current
What does the surrounding oil do?
Facilitates removal of heat
Describe the production of x-rays
Filament is electrically heated. Cloud of e- produced. A high voltage across the tube accelerates the e- to the anode at high speed. Focusing device aims the e- stream at the focal spot on the target. E- bombarded target and are brought to sudden rest. Energy lost converted to heat (99%) or X-rays (1%). Heat produced is removed and dissipated by the copper block and surrounding oil. X-rays are emitted from all directions from the target. Those emitted from the small lead free window make up the beam used for diagnostic purposes
Name the law that gives us the safe distance from a source of x-rays
Inverse square law
What is the inverse square law?
Intensity= 1/d^2
What does doubling the distance from an x-ray source do?
Reduces the intensity to 1/4
Do shorter wavelength x-rays have a greater or less energy than longer wavelength x-rays?
Greater energy
What does the photoelectric effect relate to?
Interaction with mater, not production of x-rays, this is what happens when an x-ray photon hits an object
What happens when an x-ray photon hits an object?
Compton scattering
Photoelectric effect
List 4 advantages of the photoelectric effect
- easy to learn
- accurate geometry of image
- rectangular collimator
- no dose to patient fingers, reduces repeats
What radiographs would you request for identification of an unerupted maxillary canine?
Horizontal parallax
Vertical parallax
What is parallax?
You need two views distinctly different in angulation to each other to localise it e.g if vertical go from a DPT to an occlusal, or a PP to occlusal
What are the indications for a lateral oblique of mandible?
Fracture of mandible
Pathology
Look at 8’s
What are the three different technique for lateral oblique of mandible?
Isocentric positioning
Vertical angle
Horizontal angle
What angle is the x-ray beam for isocentric positioning?
25 degrees
Who discovered x-rays and when?
Wilhelm Conrad Roentgen 1895
Each packet of x-rays is what?
A photon
What does one photon equal?
One quantum of energy
What is compton effect?
Scattering and partial absorption interaction with outer shell electrons, predominating with higher energy photons
What is the photoelectric effect?
Complete absorption interaction with inner shell electrons, predominating with lower energy photons
What are the similarities between the cathode and the anode?
Both made of tungsten
Both electrodes
Why is there a vacuum?
To allow e- to fly across
