AEC(Automatic Exposure Controls)
density
Two outside detectors activated when __________ of the body part over the 2 outside cells is close to the same density
brightness increase decrease
Optimal kVp is crucial: If kVp is changed, the AEC will compensate with an adjustment in exposure time to adjust __________ If kVp is decreased, the exposure time will automatically __________ If kVp is increased, the exposure time will automatically __________
three anatomy
Photocell/Sensors/Detectors: The radiographer selects the configuration of these devices, determining which one(s) of the ______ actually measures radiation exposure reaching the IR. Configuration is dependent on the ________ of interest
detectors; visible light photomultiplier; photodiodes large
Phototimers: Light paddles, coated with a fluorescent material, serve as the ________, and the radiation interacts with the paddles, producing what? This light is transmitted to remote ___________ tubes or ___________ that convert this light into electricity. The timer is tripped, and the radiographic exposure is terminated when a sufficiently ______ charge has been received.
Entrance or Exit Type kVp; mA Time
Position of detectors varies in 2 ways: Regardless of type, the technologist still controls the ____ and ___ ______ is controlled by AEC device
patient; electrical termination
Radiation is transmitted through the _________ and converted into an __________ signal, terminating the exposure time. A predetermined level of radiation must be reached before exposure ____________.
radiation exposure
Summary: Since visual cues lending to increased or decreased radiographic density with film/screen are not as prominent in DR, the radiographer must be very conscientious about ___________ ___________ to the patient.
Entrance Exit
The _________ type is positioned between the patient and the IR. The most common type. The ________ type is positioned after the patient and image receptor.
Outer
Which detectors do you activate for a Abdomen: Supine/Oblique/ Lateral/Upright?
All
Which detectors do you activate for a BE: AP/PA/RAO/LAO/RPO/LPO/Decub?
Center
Which detectors do you activate for a BE: Lateral?
Center
Which detectors do you activate for a Clavicle: AP/Axial?
Center
Which detectors do you activate for a Femur: AP/Lateral?
Center
Which detectors do you activate for a Hip: AP/Frog Leg Lateral?
Outer
Which detectors do you activate for a IVU?
Center
Which detectors do you activate for a Knee: AP, Oblique, Lateral?
Center
Which detectors do you activate for a Lateral Chest?
Outer
Which detectors do you activate for a PA or AP Chest?
Center
Which detectors do you activate for a Ribs: AP/PA bilateral; RAO/LAO/RPO/LPO; Lower?
Outer
Which detectors do you activate for a Ribs: AP/PA; bilateral?
Center
Which detectors do you activate for a SI Joints: AP/Obliques?
Center
Which detectors do you activate for a Shoulder: AP/Grashey?
All
Which detectors do you activate for a Small Bowel?
Center
Which detectors do you activate for a Sternum: RAO, LPO, R/L Lateral?
Center
Which detectors do you activate for a Stomach: AP/PA/RAO/LPO/R-Lateral?
Center
Which detectors do you activate for a T-Spine, L-Spine, C-Spine?
Center
Which detectors do you activate for a Tib/Fib: AP/Lateral?
Center
Which detectors do you activate for an Esophagus: RAO/AP/Lateral?
Automatic Exposure Controls
A system used to consistently control the amount of radiation reaching the image receptor by terminating the length of exposure. Began as early as 1929
exposure time brightness kVp adjusts noise decrease
AEC devices affect only what? Recall that time controls radiographic ____________, as it is part of mAs ______ influences contrast and affects radiographic brightness If a digital IR is underexposed or overexposed, the computer ________ for the exposure error, but the image quality and/or patient exposure is affected. Underexposure may result in the visibility of quantum _______, and overexposure will increase patient exposure and may __________ contrast.
electricity Phototimer & Ionization Chamber Systems
AEC systems differ by the device used to convert radiation into __________ What are the two AEC systems?
NOT DIAGNOSTIC
Activating the wrong detector will result in a image that is what?
Consistent Reduced efficiency or workload Automatic
Advantages of AEC: ____________ brightness on the images regardless of patient size and thickness. ____________ patient dose, since most exposures are correct and no need for repeats. Increase in departmental _________ or ___________, because of not having as many repeats. _____________ compensation for exposure values; even if there is an SID change.
decreases
Anatomic part has excessive gas Exposure time ___________
time BACK UP TIMER 600 mAs
Backup Timer: Recall: AEC controls the exposure _____- determined by how long it takes the exit radiation to charge the x ray timer to terminate The exposure time set on the control panel is the WHAT? *modern control panels may be automatically selecting the backup timer (at a max of ______ mAs). the following explanation is still crucial regarding AEC function
longer 1.5 600 mAs
Backup Timer: The backup timer must be set ___________ than the length of the expected exposure time (and longer than the min. response time) Typically _____ times more that what is required for the manual exposure factors for the anatomical part. FDA requires that the back up time be set as to never exceed _____ mAs
centered or unilateral
Center detectors activated when anatomy is __________ or __________ in interest
foreign bodies exposure IR collimation QC
Conditions that may cause AEC to malfunction: Do not cover detector with any ________ _________(lead, prosthesis) Selection of wrong bucky --most modern systems with sensors will not allow an ________ if an IR is not in the activated bucky Changes in ____ type --systems are calibrated for specific IRs and should not be changed Errors in _____________ --no collimation: increase scatter: premature termination --over collimation: prolonged exposure required: increase dose Neglect in _____ protocols
Detector IR Collimation Density
Film Screen: -Effect on film density- ____________ combination Part placement not covering detector(s) Type of ____ AEC calibrated to one type of image receptor ______________ Excessive or insufficient may affect exposure time _______ control Predetermined level of radiation adjusted
mA kVp SID OID
Film Screen: -No effect on film density- ______ Exposure time adjusted ______ Exposure time/contrast adjusted ______ Exposure time adjusted ______ Exposure time adjusted
underexposed
For Contrast Studies: The contrast must be placed over the detectors. If the abdomen, rather than contrast, is over the detectors, the image will be ____________.
decreases
Decreasing SID Exposure time ___________
increases
Decreasing kVp Exposure time/contrast ___________
Pathology report pathology -2; 1 25-30% QC
Density Adjustment: Allows the radiographer to adjust the amount of preset radiation detection values (for ___________ and not for patient size) Usually seen as ____, -1, 0, ____, 2 options Commonly initiates a _____% increment Routine use of these adjustments is an indication a service engineer should perform _____ calibrations
superimposed centered cover collimation
Detector Selection: Select the detector(s) that will be ________________ by the anatomy of greatest interest. The anatomy of interest must be ___________ properly over the selected detector(s). The patient's anatomy of interest must adequately _______ the detector combination. Improper ______________ may affect termination of the exposure time.
outside; center
Detector Selection: Typically, either the 2 ________ cells OR the _______ cell can be selected. Sometimes all 3
No Effect
Different types of image receptor _____ _______ on exposure time, but image quality may be affected
.50 sec .15 sec low; function
EXAMPLE: If the exposure time (manual technique) for a PA chest image is 0.20 sec., the backup time must be set longer than 0.20, such as 0.50 sec. The AEC will stop the exposure when a sufficient amount of radiation has reached the detector typically around 0.20 sec if AEC device fails, exposure will terminate at _____ sec. If the backup time was set only at 0.15 sec, the exposure will stop at _____ sec and the image will be underexposed Back up time operates under two conditions, if it is set too _____, or if AEC device does not __________ properly (operator error or mechanical error)
0.01 mA faster
Example: If the minimum reaction time is 0.01 sec., every exposure made with AEC needs to be at least _______ seconds long. Some times a problem for: -high ____ selection -pediatric -when ________ exposures are needed
increases
Excessive collimation Exposure time ___________
current directly small large timer terminated
How AEC functions: Exit radiation from the patient interacts with the detector, producing a _______ Strength of the current is ________ proportional to the exit radiation interacting with the detector So therefore, ______ current produced with a small amount of exit radiation ______ current produced with a large amount of exit radiation The current produced in the detector charges the xray _______ When the x ray timer receives a predetermined amount of charge from the detector, the x ray exposure is ___________
edge short; underexposure
If the _______ of a body part is positioned over the detector, the detector will detect some of the body part and some of the blank space. This will result in a _____ exposure and _____________.
increases
Increase patient thickness Exposure time ____________
increases
Increased density adjustment Exposure time ____________
increases
Increasing OID Exposure time ___________
decreases
Increasing mA Exposure time ___________
air electrical charge wire large
Ionization Chamber System: A hollow cell that contains ____ and is connected to the timer circuit by electrical wire. Ionization chamber is exposed, and the air inside the chamber becomes ionized, creating an _________ ________. Charge travels along the ______ to the timer circuit. The timer is tripped, and the radiographic exposure is terminated when a sufficiently ________ charge has been received.
terminate inherent underexposed 1 ms; (0.001)
The minimum reaction time is the shortest time it takes for the detector(s) to function and _________ the exposure. It is __________ in each system. If back up timer is set lower than the reaction time, AEC will not function properly and result in an image that is _______________ ____ ms in modern units (_______ s)
Photocell/Sensors/Detectors
The part of the AEC which detects when the desired amount of radiation has been received to achieve the desired IR brightness A set of three radiation-measuring detectors, arranged in some specific manner.
Ionization Chamber System
This represents which AEC system?
Phototimers
This represents which AEC system?
kVp mA detector arrangment density adjustment backup timer
When employing an AEC device, the radiographer will select the following settings on the control panel: (5)
5-6 NOT large
When the Backup time can be set: Many radiographers set the backup timer too high so that it is ___-___ times longer than the expected exposure time Do ______ set the backup time too high If AEC does not work, the patient will receive a _______ exposure
Outer
Which detectors do you activate for a AP Pelvis?
Center
Which detectors do you activate for a AP/Lateral Humerus?
Center
Which detectors do you activate for a Abdomen: Left Lateral Decub?
Ordinary
_________ detector arrangement
brightness mA
mA settings: Any mA can be selected for the image to produce an "optimum ___________" image, however... **the higher the ____, the lower the time
displayed feedback familiarity
mAs Readout: When AEC is employed, the total amount of mAs required to produce the IR exposure is determined by the system. This actual mAs amount is ____________ immediately after the exposure, sometimes just briefly. It is so important for the radiographer to take note of this readout -Can give immediate _________ on accuracy -Can help improve _____________ with exposure factors --Especially useful when imaging additional projections for the same patient