| Question | Answer |
| What are the 4 primary exposure factors? | Kvp
Ma
Time
SID |
| What does each control | |
| Mas | Ma x time =Mas |
| Is this a direct or indirect relationship? | |
| when ever you see distance its what? | Squared |
| Whenever you see time you convert it to what? | A decimal |
| Alara | Cr/dr -histogram |
| Purpose of technique charts | Reference for technique selection for anatomic area. Should be room/specific due to equipment. Considers pathology. |
| If a caliper is used to measure pt. Thickness were should you measure | at CR level |
| Variable kvp chart | Mas remains constant. Kvp values according to part thickness. List baseline kv and use +2 kv per cm |
| What are the disadvantages of a variable kvp chart | variable contrast |
| What are the advantages of a variable kvp chart | Less pt dose (because mas is constant) |
| Fixed kvp chart | Mas varies, is altered for part thickness. Requires at least 30% change to see. |
| 100% doubles 50% halves | |
| Advantage of a fixed kvp chart | Contrast does not change |
| Disadvantage of a fixed kvp chart | Pt. Dose increases (because your increasing your mas |
| Which chart is better for children | Fixed kvp chart because we can lower our mas |
| chart development | Phantoms, calipers, calculator, objective/subjective- Bt, Std & high contrast |
| When using a variable kvp chart what must be down in order to select kv | A measurement using calipers |
| rules of thumb for peds | infants 0-2 use 1/4 0f mas
pre school 2-6 use 1/2 of mas
school 6-12 use 3/4 of mas
teens >12 no change |
| casts: rule of thumb dry plaster | plaster- dry is easier to penetrate
2 x mas or increase 10 kv |
| casts: rule of thumb wet plaster | plaster- wet is harder to penetrate
3 x mas or increase 15 kv |
| casts: fiberglass | increase 5 kv |
| beam restriction: rules of thumb when collimating | from 14x 17 to 10 x 12 from 14x 17 to 8x 10
40% more mas or +5 kv 60% more mas or +10 kv |
| how are ma and time related | indirectly |
| ma controls | quantity and density |
| time controls | motion and recorded detail |
| technique conversion formula for ma and time | ma x t = mas ma1= t2
ma2 t1 |
| technique conversion formula for mas and distance | based upon isl (what is law and formula)
mas1=(sid1)2 if no time just use ma
mas2 (sid2)2 if no ma just use time
DISTANCE IS ALWAYS SQUARED IN FORMULAS |
| how are mas and distance related | direct relationship |
| technique conversion formulas | 15% kvp rule: if increase kvp by 15% will double density and decrease contrast
if decrease kvp by 15% will half density and increase contrast |
| compensation for changes in kvp to change contrast but maintain density | incr. 15%= 1/2 mas (50%)
decr. 15%= 2 x mas (100%) |
