exposures review Flashcards
what is now recommended with digital detectors - reduces ESE (entrance skin exposure)
higher kVp
higher SID means
lower dose - loses energy when all other factors remain unchanged
higher OID reduces
overall exposure & increases magnification
reducing scatter overall
reduces dose
good right collimation lowers
dose& scatter therefore exposure
patients thickness
reduces exposure , when all other factors remain unchanged
increase factors for
grids
added filtration
lowers exposure
greater signal =
better images with less noise or graininess
what is detector saturation
excessive signal (exposure) gives no added visible improvement and adds to dose
to lower entrance skin exposure
up kVp, lower mAs
exposure technique charts
help produce consistent images, 2 types
fixed kVp
establish optimal kVp range, appropriate contrast w in acceptable limits. !!mAs is adjusted in increments of min. 30% (double or halve mAs for every 5 cm of subject thickness!! helps to decrease patient dose
fixed kVp is better suited for
DR systems - the rules are not as strict
variable kVp
2 kvp per cm of subject thickness + base kvp
2kvp times part cm +30kvp = new kvp
* consistent with the 15% rule while ensuring sufficient penetration
dose creep happens when
using a wide latitude
dose creep
wide exposure latitude with digital imaging, errors in technique selection are being made on the additive side for correction
EI number
evaluates how much exposure hit the IR
EI target number provide
reliable techniques based on exam type, projection, patient thickness
Automatic Exposure Control (AEC)
work well with CR & DR, used to help with ALARA, requires precise positioning of part for accurate exposure
DI (deviation index) number
determines the amount of over or under exposure
DI number increments
are set at 20% for underexposure , and 25% for overexposure
-2 would be an underexposure of
40% below
+2 would be an overexposure of
50% above recommended target
