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Ch 10, 11 Rad Protec

Equipment design for Rad Protect; Managment of pt rad dose during xrays

QuestionAnswer
Collimators Defines size and shape of the radiographic beam. -Aperture diaphragm -Cones
PBL Positive beam limitation; A feature of current radiographic collimators that automatically adjusts the collimators so that the radiation field size matches the film size
Collimation Internal beam limitation starts with the upper shutters, then the lower shutters which are controlled by the radiographer; -Stops the production of scatter radiation by reducing off-focus or stem radiation -Reduces patient exposure
How far does a pts skin have to be away from collimators 15cms below collimator
Inherant filtration Includes the glass envelope encasing the tube, the insulating oil surrounding the tube, the glass window if the tube housing; .5mmAl Equivalent
Added filtration Consists of sheets of Al added outside the glass window above the collimator. This along w/ inherent filtration should equal 2.5 mm Al equivalent -For xray units above 70KVP -2.0mm Al equivalent
Filtration (4) Reduces the exposure to the patient’s skin and superficial tissue by absorbing most of the lower-energy photons; hardens the beam; increases quality, decreases overall intensity of radiation
4 types of gonadal shielding Flat contact shield, shadow shields, shaped contact shield, clear lead
Compensating filters are Aluminum or lead inserted between the s-ray source and the patient to modify the quality of the beam across the field of view
Compensating filters partially.. attenuate x-rays that are directed toward the thinner, or less dense area while permitting more x-radiation to strike the thicker, more dense area
Wedge filter Comp Filter; used to produce uniform density when radiographing a structure of varying densitys
Trough filter Comp filter; bilateral wedge filter the filter is thin in the center and the sides are thicker
Tech factors for pt protection Use higher kvp and lower mas. As kVp increases & mAs decreases there is a reduction in contrast. Must be a balance
95% of the radiographic density on a film results from the light emitted from the intensifying screens
Rare earth screens are 15-20% faster
Speed increases when When the amount of the silver halide in the film is increased
Radiographic Grid Never used for tissue less then 10cm. Remove the scatter radiation, before it hits the film. Added or increasing the grid ratio requires the radiographer to increase their technical factors.
Air Gap Grid Requires 6-10inch OID. Alternative procedure to the use of the grid. Reduces the amount of scatter reaching the film because it is absorbed in the air or scattered away from the film.
Source skin distance SSD must be at least 12 inches (30cm)
C-arm minimal source to end distance 12 inches
Pt average dose for mammo Less than 200mrad per view
Skull, body dose for CT 1-3 rad for skull, 2-6rad for body
Created by: rachelbeatty4