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what are the 4 primary exposure factors
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mA x time=
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Exposure Factors
Primary Exposure Factors
| Question | Answer |
|---|---|
| what are the 4 primary exposure factors | *ma *kVp *time *SID |
| mA x time= | mAs |
| what is the k shell binding energy for bone | 16 |
| what does mA control | quantity of radiation/density/brightness |
| what does kVp control | quality/penetration/speed/contrast |
| what is the purpose of technique charts | *reference for technique selection for anatomic area *should be room/facility specific due to equipment calibration *considers pathology *if using a caliper to measure pt thickness, measure at CR level |
| what are the two types of technique charts | *fixed kVp *variable kVp |
| what happens with a variable kVp chart | *mAs remains constant *kV varies according to part thickness *lists baseline kV and uses + or - 2 kV per cm *allows you to lower pt. dose *disadvantage is; with more kVp contrast is lowered |
| what happens with a fixed kVp chart | *mAs is altered for part thickness *requires at least 30% change to see *100% change(2x) doubles density; 50% change(1/2) halves density *advantage is contrast is not changed *disadvantage is more pt dose |
| no amount of _______ can make up for inadequate _______ | mAs/kVp |
| what equipment is used to develop technique charts | *phantoms *calipers *calculator *objective v. subjective |
| what are the rules of thumb regarding mAs compensation for adults vs pediatric patients | *infants(0-2 yrs)-use 1/4 of mAs *preschool(2-6 yrs)-use 1/2 of mAs *school age(6-12 yrs)-use 3/4 of mAs *teens (>12)-no change |
| what are the rules of thumb regarding technique with a cast | *dry plaster cast-2x mAs or +10 kVp *wet plaster cast-3x mAs or +15 kVp *fiberglass cast- +5 kVp |
| what are the rules for technique change when collimating | *14 x 17 to 10 x 12- 40% more mAs or +5 kVp *14 x 17 to 8 x 10- 60% more mAs or +10 kVp |
| what does time control | motion/recorded detail |
| what is the mAs formula | *mA x time *mA1/mA2=t2/t1 *indirect relationship between mA and time |
| what is the mAs distance formula | *mAs1/mAs2=SID1 squared/SID2 squared *applied when unable to get optimal distance *based upon inverse square law *if no time just use mA to calculate *if no mA just use time to calculate **distance must always be squared *direct relationship |
| what is the 15% kVp rule | *if kVp is increased by 15% it will double density and decrease contrast *if kVp is decreased by 15% it will half density and increase contrast *compensation in mAs is used to change contrast but maintain density *(15% + kVp=1/2 mAs & 15%- kVp=2x mAs)* |
| what is the inverse square law | I1/I2=D2 squared/D1 squared *the intensity of radiation is inversely related to distance squared |
| what are the magnification formulas | *image size/object size *percent mag=oid/sod *mag factor=sid/sod |
| what are the grid conversions for mAs | *x2--5:1 ratio *x3--6:1 ratio *x4--8:1 ratio *x5--10 or 12:1 ratio *x6--16:1 ratio |
| what are the grid conversions for kVp | *5:1-- +8-10 *6:1-- +11-12 *8:1-- +13-15 *10 or 12:1-- +20-25 *16:1-- +30-40 |
| how do you calculate screen conversion | divide speed by 100 |
| what is the PE formula | *photographic effect *numerical representation of optical density *PE= (mAxtxkVp squared/SID squared)x IR/grid *if factor missing, leave out of equation |
| what are the two types of xray equipment we use in relation to xray current | *single phase to 3-phase(1/2 mAs or drop 10 kVp) *3-phase to single phase(2x mAs or +10 kVp) |
| what is the advantage of 3 phase equipment | gives more output and allows you to use less technique |
| what is a 3 phase AC | 3 phases of alternating current, rectifiers eliminate negative current allowing more output |
Created by:
bigad1982
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