There's a fair amount of stuff on the this subject on-line, Roman. But here (for what it's worth) are some of my own notes. Something to be going on with, perhaps:-
1)
Intensity is proportional to mA.
2)
Penetration is proportional to kVp.
3) Film blackening is an indication of the
amount of x-rays, which is proportional to mAs.
1 MeV Radiation Therapy
300 kV Hard X-Rays
100 kV Hard-Soft X-rays
20 kV Soft X-Rays
Exposure Techniques:-
3-factors (or 3-knob, or 3-point)
kV, mAs and time are set
2-factors (or 2-knob, or 2-point)
kV and mAs are set (unit should give shortest possible time)
1-factor (or 1-knob, or 1 point)
kV only is set (exposure is terminated by Automatic Exposure Control; Siemens "Iontomat" etc.). Generator will generally use "falling load".
0-factor (or 0 point)
kV is determined from fluoro data, and is terminated by Automatic Exposure Control.
X-Ray Film:-
1) Transparent plastic base material coated with radiation- sensitive emulsion (...this contains a suspension of minute silver-bromide crystals embedded in gelatin).
2) Where radiation falls on the emulsion, a few silver-bromide molecules in each grain are reduced to silver.
3) During developing, the few silver atoms in each grain act as catalysts, so that the silver-bromide grain is reduced to silver (a catalyst is a substance that does not itself change, but speeds up a chemical reaction). Light is absorbed strongly in regions of the film containing silver grains, producing regions of blackness. Where smaller amounts of radiation fall, the film is grey. In areas where no radiation has reached, the film remains almost transparent (...a totally transparent radiograph usually indicates that no exposure has taken place)!
4) During fixing, undeveloped silver-bromide is removed (or else this would cause the film to slowly continue to blacken when exposed to light). This is done by dissolving the silver-bromide in sodium thiosulphite ("fixer"), which also hardens the gelatin of the emulsion. The fixer overflow-drain is usually led away to a silver recovery unit, wherein silver adheres to carbon electrodes for collection later.
5) The film is then washed in water to remove residual chemicals, as these would form streaks across the film when dry.
Intensifying screens:-
1) Used to effectively increase film speed, and so reduce the amount of radiation needed. They consist of thin layers of high-atomic-number phosphor coated on a base material. Intensifying action action arises as more of the x-rays are absorbed and a large number of light photons are given off to blacken the film.
2) A common screen material is calcium tungstate, which has an amplification effect of about 30 (...thus, instead of a 300 mR dose to the patient's skin, dose can be reduced to 10 mR). Light emitted from this screen is at the wavelength of the colour violet (...corresponding to maximum sensitivity of the film).
3) Intensifying screens are used in pairs, almost always inside a film cassette (in which they usually remain) with the film itself sandwiched between the two screens.
Servicing of X-Ray Equipment:-
1) Follow the usual "drill":-
a) Check and Clean it
b) Replace and/or Repair it
c) Tighten and Lubricate it
d) Adjust and/or Calibrate it
2) It should be noted that proper servicing of major x-ray systems takes many hours. A "repair as you go" approach is usually needed to fully check, test and "make good".
QA tests checklist:-
The basic criteria are whether the unit consistently produces radiographs of sufficient quality for clinical diagnosis. This must also be achieved safely and at the lowest achievable dose. Ideally, regular Quality Assurance (QA) tests should be performed as follows (note that special test equipment is needed for these):-
1) kV
2) mA
3) HVL (Half Value Layer)
4) mAs linearity (at various kV)
5) Dose
6) Beam alignment (collimator -v- x-ray beam)
Equipment needed (in addition to normal tools, multimeter and service consumables):-
1) Step ladders
2) Storage oscilloscope
3) mAs meter
4) Non-invasive x-ray output meter
