Chapter 14 Notes Flashcards
the maximum dose received by the patient is where
at the skin entrance to the body
formula for entrance skin exposure
mR/mAs
formula for fluoroscopy entrance skin exposure
R/min
exposure is
radiation intensity in air
exposure is measured in
roentgens (R)
dose is
the amount of radiation absorbed
dose is measured in
rad
entrance skin exposure is calculated at
minimum SOD
it is better to _____ exposure, rather than _____ exposure
overestimate; underestimate
mR/mAs charts are typically calculated at what distance
40 inches SID (100 cm)
higher kVp’s produce _____ mR/mAs
higher
FDA limit for standard fluoroscopy exposure rates
11.5 R/min (10 cGy/min)
FDA limit for high-level control fluoroscopy exposure rates
23 R/min (20 cGy/min)
what is the interrelationship of prime factors
(mAs)x(kVp squared)/(distance squared)
increasing kVp without compensation in mAs will
increase patient dose
increasing kVp with a compensation in mAs will
decrease patient dose
increasing mAs without compensation from other technical factors will
increase patient dose
mAs at the lowest level possible will
reduce patient dose
an increase in SID or SOD results in
decrease in entrance skin exposure (ESE)
a decrease in OID will
increase SOD and decrease ESE
increased filtration will decrease ESE with
modification in kVp
increased filtration will increase ESE with
modification in mAs to maintain image quality
a decrease in primary beam size will
decrease patient dose
a significant decrease in field size will often require
an increase in mAs
three major types of gonad shielding
flat contact, shadow, and shaped contact
a higher ratio grid will
require increase in mAs and increases patient dose
use lowest ratio grid necessary to
minimize patient dose
use of an intensifying screen will
reduce dose (faster screen speed)
use of film will
decrease dose (increases film speed)
use of film processing will
have no effect on dose when properly maintianed
digital image receptor systems respond to
0.01 mR to 100 mR
what percent of radiation exposure received by the general public is a result of diagnostic radiographic examinations
15%
which radiographic exams result in the highest ESEs
L-spine, pelvis, and hip
when area of interest is as close to IR as possible
increased recorded detail, decreased distortion, and places area as far from entrance exposure as possible
immobilization will
eliminate motion, decrease tissue density through compression, and reduces dose
what percent of repeats are the result of improper technical factors
> 50%
increasing the number of pulses from the generator will
cause substantial decrease in patient ESE
k-edge is created by
characteristic photons
characteristic photons interact with matter through
photoelectric interactions
mAs has a _____ relationship with exposure
direct
increasing filtration will
reduce ESE, even when kVp is compensated
increased field size will
increase total dose, even when mAs or kVp are adjusted
flat contact shield
positioned over gonads at skin surface
shadow shield
positioned in primary beam below collimator
shaped contact
worn by patient to surround gonads
what region does not permit the use of shields
pelvic region
decreasing subject part density
decreases scatter production and reduces patient dose
using a higher speed film will
decrease dose
most acceptable images produced use about _____ exposure to receptor
1 mR
asymptomatic patients should only be examined when
is significant cause; after considering incidence and severity of condition; detection reliability of exam; usefulness of exam in treatment
symptomatic patients should fit what two criteria for x-ray exams
exam is capable of providing desired information; the information, if negative, is expected to contribute to the management of the patient
establish credibility with patient by
answering questions; taking medical history; manipulate x-ray equipment; and exhibiting a professional demeanor
Proceeding with an exam after a patient refuses puts the radiographer at risk of malpractice action. This is usually as
assault and battery
