Ch. 13 Exposure Technique Selection Flashcards
a system that controls the duration of the exposure, thereby controlling the amount of radiation that is used
AEC - automatic exposure control
what are the 2 types of AEC radiation detector systems
- phototimers
- ionization chambers
these use a fluorescent screen coupled with a photomultiplier (PM) tube or a photodiode
phototimers
these convert light into electrical signal
photomulitplier (PM) tubes and photodiodes
phototimer AECs are what type of devices
exit-type - radiation passes through the IR before it can be measure and used to terminate exposure
what are most AEC devices now
ionization chambers
a hollow cell filled with air, connected to a timer circuit via electrical wire
ionization chamber
ionization chambers are what type of devices
entrance-type - positioned in front of the IR
what do ionization chambers measure
DAP
which AEC device is less sophisticated and less accurate
ionization chambers
which AEC device is less prone for failure
ionization chambers
AEC only controls this
quantity of radiation
does AEC have an effect on contrast
no
using a higher kVp with AEC will result in this
shorter exposure time
using lower kVp with AEC will result in this
longer exposure time
lower mA will result in this
longer exposure time
this is the shortest exposure time that a system can produce
minimum response
is minimum response time usually longer with AEC systems
yes
maximum length of time an exposure can go when using AEC
backup time
when setting a backup timer, the tech should set it to terminate the exposure at what percent of the desired exposure
150-200%
exposure adjustment is also known as this
density controls
AEC is designed to compensate for changes in this
patient thickness
destructive pathologies may cause this (using AEC)
underexposure
additive pathologies can cause this (using AEC)
overexposure
a series of pre-built exposure techniques that a radiographer can quickly select from when preparing to image a patient
anatomic programming
exposures need to be able to be reproduced using the same technical factors that provide mR reading within ___% of each other, and with pixel brightness levels within ___% of each other
5%, 30%
how much is kVp increased for every cm increase in part thickness
2
mAs is adjusted by a factor of 2 for every how many cm change in part thickness
4-5 cm
do fiberglass casts require technique change
no
do plaster casts require technique changes
yes
do splints require a technique change
not unless stabilizing piece is over anatomy of interest
if the disease is an additive pathology what do you need to do to technique
increase
if the disease is a destructive pathology what do you need to do to technique
decrease
how does positive contrast show up on an x-ray
lighter
how does negative contrast show up on an x-ray
darker
what might you need to do to technique when using a positive contrast
increase
what might you need to do to technique when using a negative contrast
typically no change
what type of disease is an aortic aneurysm
additive
what type of disease is ascites
additive
what type of disease is cirrhosis
additive
what type of disease is hypertrophy
additive
what type of disease is a bowel obstruction
destructive
what type of disease is free air
destructive
what type of disease is atelectasis
additive
what type of disease is congestive heart failure
additive
what type of disease is malignancy
additive
what type of disease is pleural effusion
additive
what type of disease is pneumonia
additive
what type of disease is emphysema
destructive
what type of disease is pneumothorax
destructive
what type of disease is hydrocephalus
additive
what type of disease is metastases (osteoblastic)
additive
what type of disease is osteochondroma
additive
what type of disease is paget disease (late stage)
additive
what type of disease is gout
destructive
what type of disease is metastases (osteolytic)
destructive
what type of disease is multiple myeloma
destructive
what type of disease is paget disease (early stage)
destructive
what type of disease is an abscess
additive
what type of disease is edema
additive
what type of disease is sclerosis
additive
what type of disease is atrophy
destructive
what type of disease is emaciation
destructive
what type of disease is malnutrition
destructive
diseases or conditions that increase the absorption characteristics of the part, making it more difficult to penetrate
additive diseases
diseases or conditions that decrease the absorption characteristics of the part, making the part less difficult to penetrate
destructive diseases