7. Radiographic Equipment Flashcards
a device that measures the quantity of radiation reaches the image receptor
Automatic Exposure Control (AEC)
it automatically terminates exposure when IR has received that required radiation intensity
Automatic Exposure Control (AEC)
AEC systems also are called
automatic exposure devices
once a predetermined amount of radiation is transmitted through a patient, the x-ray exposure is terminated
Automatic Exposure Control (AEC)
this determines the exposure time and therefore the total amount of radiation exposure to the image receptor
Automatic Exposure Control (AEC)
2 Types of AEC System
- Phototimers
* Ionization Chamber
specifically refers to the use of an AEC device that uses photomultiplier tubes or photodiodes
Phototiming
are the AEC devices that measure the amount of radiation transmitted
Detectors
used for exposure timer checks
Solid-state Radiation Detectors
operate with a very accurate internal clock based on a quartz-crystal oscillator
Solid-state Radiation Detectors
fluorescent (light-producing) screen and a device that converts the light to electricity
Phototimers
an electronic device that converts visible light energy into electrical energy
Photomultiplier Tube (PMT)
is a solid-state device that performs the same function of a PMT
photodiode
also called exit-type devices
Photomultiplier Tube (PMT)
flat, parallel plate ______ positioned between the patient and the image receptor
Ionization Chamber
a hollow cell that contains air and is connected to the timer circuit via an electrical wire
Ionization Chamber
considered as entrance-type devices
Ionization Chamber
less sophisticated, less accurate, less prone to failure
Ionization Chamber
interacts with exit radiation before it reaches the image receptor
Ionization Chamber
air in the chamber is ionized and electric charge that is proportional to the amount of radiation is created
Ionization Chamber
If the radiographic unit has a mAs readout display, the radiographer should observe the reading ____ the exposure is made
after
The radiographer must be sure to set the ___ value as needed to ensure adequate penetration and to produce the appropriate scale of contrast
kVp
The ___ selected determines the length of exposure time when using AEC
kVp
A ___ kVp required more exposure time when using AEC
low
requires more exposure time to reach the predetermined amount of exposure
low kVp
decreases the exposure time to reach the predetermined amount of exposure and reduces the overall radiation exposure to the patient
high kVp
If the radiographer can set the __ when using AEC, it affects the time of exposure for a given procedure
mA
Increasing the mA _____ the exposure time to reach the predetermined amount of exposure
decreases
Decreasing the mA _____ exposure time to reach the predetermined amount of exposure
increases
Refers to the shortest exposure time that the system can produce
Minimum Response Time
Minimum response time usually is ____ with AEC systems than with other types of radiographic timers
longer
If the minimum response time is longer than the amount of time needed to terminate the exposure, an _____ amount of radiation reaches the image receptor
increased
Refers to the maximum length of the time the x-ray exposure continues when using an AEC system
Backup Time
acts as safety mechanism when AEC System fails or equipment is not used properly
Backup Time
Protects the patient from unnecessary exposure and protects the x-ray tube from reaching or exceeding its heat-loading capacity
Backup Time
If the back-up time is controlled automatically, it should terminate at a maximum of ___ mAs
600 mAs
When in AEC mode, the electronic timer should be set to ___ times the expected exposure time as back-up timer in case the AEC fails
1.5 times
Backup time should be at _____ of the expected exposure time. This allows the properly used AEC system to appropriately terminate the exposure, but protects the patient and tube from excessive exposure if a problem occurs
150% to 200%
To _____ patient exposure, the backup time should be neither too long or too short
minimize
The combination of _____ affect the amount of exposure reaching the image receptor
detectors
If the area of radiographic interest is not directly over the selected detectors, that area probably will be
over-or underexposed
When performing any radiographic study in which the image receptor is located outside of the Bucky, the ____ should be deactivated and a manual technique used
AEC system
Accurate centering of the area of interest over the detectors is ____ to ensure proper exposure to the image receptor
critical
If the area of interest is not properly centered to the image receptor, ______ may occur
over-or underexposure
The ___ of the detectors used within an AEC system is fixed and cannot be adjusted
size
If the detector combination is larger than the area of interest, a ____ exposure technique should be used
manual
____ factors affect the time the exposure takes to reach the image receptor and ultimately affect image quality
Patient
Variations in patient _____ result in changes in the time of exposure accordingly if AEC system is functioning properly
thickness
Pathologic conditions, contrast media, foreign objects, or pockets of gas are ______ that may affect the proper exposure to the IR and ultimately image quality
patient variations
Excessive or insufficient _____ may affect the amount of exposure reaching the image receptor
collimation
Insufficient collimation may result in excessive ____ reaching the detectors, resulting in the exposure time terminating too quickly
scatter
Excessive collimation may result in an exposure time that is too ___
long
is calibrated to the type and speed of the IR used
AEC System
If an image receptor of a different type or speed is used, the detectors will not sense the difference, the exposure time will terminate at the preset value, and image quality may be _____
jeopardized
Refers to a radiographic system that allows the radiographer to select a particular button on the control panel that represents an anatomic area; a pre-programmed set of exposure factors can be selected
Anatomically Programmed Radiography (APR)
are not related in their function
APR and AEC
The purpose of ______ is to ensure that consistent and appropriate exposures to the image receptor are produced
calibration
Failure to maintain regular _____ of the unit results in the lack of consistent and reproducible exposures to the detectors and could affect image quality
calibration
is important in monitoring the performance of the AEC system
Quality Control
Optical densities should be within ____ and reproducibility of the exposures for a given set of exposure factors and selected detector should result in mR readings within __ and optical densities within ____
+/- 0.2,
5%,
+/- 0.10
