AEC Questions
What is phototiming?
-Old term -Exit device that converts x-rays to light, then light into an electrical signal
What are some destructive pathologies?
-emphysema -pneumothorax -osteoporosis
What are some additive pathologies?
-pleural effusion -pneumonia -ascites
to compensate for an additive pathology, the radiographer should increase mas by: -0% -5-15% -15-25% -25-50%
0%
place an A if the center photocell should be used and a B if the two outside photocells should be used. 1. Lateral chest 2. AP pelvis 3. PA chest 4. AP left hip
1-A 2-B 3-B 4-A
What does the density controls do?
change exposure by a predetermined amount (usually 25% each step-increase/decrease) 0 is neutral/normal density
Which one of these changes will produce a radiograph demonstrating more IR exposure when using AECs? a. Increase the mA b. Increase the backup time c. Increase the kVp d. Increase the density setting above normal
d. Increase the density setting above normal -Density setting is used for IR exposure for image quality
What is the primary purpose of AEC?
control the amount of radiation that reaches the IR. No need for the radiographer to set a time
What is the backup timer?
maximum length of time x-ray exposure will continue when using AEC
What does the backup timer need to be set at?
150% of expected exposure time of manual technique -maximum 600 mAs above 50 kVp
For an AP L-spine exam the manual technique for is 35 mAs @ 80 kVp. What backup time should the radiographer set? -8 mAs -52.5 seconds -52.5 mAs -8 seconds
52.5 mAs
The back-up timer terminates the exposure when the total milliampere-seconds (mAs) has reached: 100 mAs 300 mAs 600 mAs 1,200 mAs
600 mAs
What is an ionization chamber?
An entrance device that receives exposure, air in chamber becomes ionized creating an electrical charge once that charge is complete the exposure will terminate
What is AEC?
Automatic Exposure Control. A device that measures pre-set quantity of radiation and stops timer when sufficient radiation is produced for IR exposure
When using automatic exposure control (AEC), the technologist cannot directly assign which of the following parameters? -Kilovoltage peak (kVp) -Source-to-image distance (SID) -Object-to-image distance (OID) -Milliampere-seconds (mAs)
Milliampere-seconds (mAs)
The backup time should be set: a. Above the expected manual exposure time b. Below the expected manual exposure time c. Equal to the expected manual exposure time d. At 1 second for any and all exposures
a. Above the expected manual exposure time -It should be set above the expected manual exposure time because it is the maximum length of time in order to prevent overexposure. It terminates 150% of the expected time and at 600 mAs.
When using AECs, if the centering point for a lateral knee is at the patella and the center photocell is used: a. The radiograph will be too light b. The radiograph will be too dark c. The radiograph should be good
a. The radiograph will be too light -The patella won't cover the cell completely, so the primary beam will hit it faster and shut off earlier resulting in an underexposed image.
When using automatic exposure control with the center photocell activated, if the centering point for an AP lumbar spine is over the liver instead of over the spine: a. The radiograph will be too light b. The radiograph will be too dark c. The radiograph will be perfect!
a. The radiograph will be too light The radiograph will be too light because the liver is a less dense/thick part compared to the spine. AEC compensates for part thickness, so the exposure time will be less and therefore too light.
What type of pathology needs an increase in technical factors?
additive pathology -images using manual technique selection would appear underexposed unless you compensate for the increase in patient thickness by increasing your technical factors (typically 5-15% kvp)
What will under collimating (leaving light field wide open) do to an image when using AEC?
adds scatter which causes cells to receive unwanted density to AEC and terminates exposure to soon causing an underexposed image (to light)
Which of these is NOT a type of detector in an AEC system? -air chambers -phototimer -ionization chambers -enterance type
air chambers
When using automatic exposure control with the center photocell activated, if the centering point for a lateral chest is a the level of T-11 instead of at T-6: a. The radiograph will be too light b. The radiograph will be too dark c. The radiograph will be "just right"
b. The radiograph will be too dark -The material is thicker at the level of T-11 so you need to use more mAs. More mAs would lead to more exposure and be darker.
If a low mA is selected, the automatic exposure control will: a. Produce a radiograph with less IR exposure b. Use a long exposure time c. Increase the kVp d. Produce a radiograph with more IR exposure
b. Use a long exposure time -AEC controls time, so if mA decreases than AEC compensates for a longer exposure time.
Which one of these changes will produce a radiograph with higher contrast when using AECs? a. Decrease the mA b. Increase the backup time c. Decrease the kVp d. Decrease the density setting below normal
c. Decrease the kVp -Low kVp= high contrast, short scale with more black and white. Low kVp produces less scatter
Which of these would be the best for a radiographer to do to control motion when using automatic exposure control? a. Decrease the backup time b. Increase the kVp c. Use a high mA d. Use a density setting lower than normal
c. Use a high mA -When using a high mA the AEC compensates for a shorter exposure time.
What technical change is required to decrease receptor exposure when using automatic exposure control (AEC)? -Increased milliamperage (mA) -Decreased kilovoltage peak (kVp) -Increased back-up timer -Decreased density setting
decreased density setting
Which of the following effects is observed when using automatic exposure control (AEC) to image a hyposthenic patient? -Decreased spatial resolution -Increased contrast resolution -Increased receptor exposure -Decreased exposure time
decreased exposure time
Which of the following effects will occur when using an automatic exposure control (AEC) system to image a hyposthenic patient? -Decreased spatial resolution -Increased contrast resolution -Increased receptor exposure -Decreased exposure time
decreased exposure time
When performing a lateral cervical spine using an automatic exposure control (AEC) system, the technologist activates the outer ionization chambers. How might this affect the radiographic image? -Increased exposure time and decreased receptor exposure -Increased exposure time and increased receptor exposure -Decreased exposure time and increased receptor exposure -Decreased exposure time and decreased receptor exposure
decreased exposure time and decreased receptor exposure
When using automatic exposure control (AEC), which of the following technical changes will increase the total exposure time without increasing the receptor exposure? -Decreased milliamperage (mA) -Increased kilovoltage peak (kVp) -Decreased back-up timer -Increased density setting
decreased milliamperage (mA)
When performing an anteroposterior (AP) lumbar spine using an automatic exposure control (AEC) system, the technologist inadvertently positions the patient with the active ionization chamber under a gas pocket in the abdomen. How will this affect the radiographic image? -Decreased spatial resolution -Decreased image contrast -Increased distortion -Decreased receptor exposure
decreased receptor exposure
What type of pathology needs a decrease in technical factors?
destructive pathology -images using manual technique selection would appear overexposed unless you compensate for the decrease in patient thickness by decreasing your technical factors (typically mAs by 25-50%)
The automatic exposure control (AEC) system communicates with which portion of the x-ray circuit when the optimal receptor exposure has been achieved? -Filament circuit -Autotransformer -Milliampere (mA) selector -Exposure timer
exposure timer
If to much exposure occurs, AEC will adjust the kvp lower to compensate? -true -false
false
What is an operational amplifier?
if more than one chamber is activated, the exposure is averaged between them all
A radiograph of the lumbar spine is produced using automatic exposure control (AEC). The exposure results in optimal contrast but low receptor exposure. What is the ideal way to increase receptor exposure? -Increase milliamperage (mA) -Increase kilovoltage peak (kVp) -Decrease grid ratio -Increase density setting
increase density setting
Which of the following effects will occur when using an automatic exposure control (AEC) system to image a hypersthenic patient? -Increased spatial resolution -Decreased contrast resolution -Decreased receptor exposure -Increased exposure time
increase exposure time
When using a radiographic unit with automatic exposure control (AEC), which of the following can be employed to reduce patient motion while maintaining proper receptor exposure? -Increase milliamperage (mA) -Decrease kilovoltage peak (kVp) -Increase back-up timer -Decrease density setting
increase milliamperage (mA)
What technical change is required to increase receptor exposure when using automatic exposure control (AEC)? -Increased milliamperage (mA) -Increased density setting -Decreased kilovoltage (kVp) -Decreased back-up timer
increased density setting
A technologist is performing an anteroposterior (AP) abdomen radiograph on a geriatric patient using an automatic exposure control (AEC) system. Which of the following changes will be noted if the technologist decreases the kilovoltage peak (kVp)? -Decreased patient dose -Increased receptor exposure -Decreased contrast -Increased exposure time
increased exposure time
A technologist performing an anteroposterior (AP) pelvis projection unintentionally places gonadal shielding over two of the three active automatic exposure control (AEC) ionization chambers. How will this affect the exposure time and patient dose? -Decreased exposure time and decreased patient dose -Decreased exposure time and increased patient dose -Increased exposure time and decreased patient dose -Increased exposure time and increased patient dose
increased exposure time and increased patient dose
When performing a posteroanterior (PA) chest radiograph using an automatic exposure control (AEC) system, the technologist engages only the center AEC ionization chamber. How might this affect the radiographic image? -Increased exposure time and decreased receptor exposure -Increased exposure time and increased receptor exposure -Decreased exposure time and increased receptor exposure -Decreased exposure time and decreased receptor exposure
increased exposure time and increased receptor exposure
Which modifications may decrease the total exposure time when using an automatic exposure control (AEC) system? -Increased milliamperage (mA) -Decreased kilovoltage peak (kVp) -Decreased back-up timer -Increased density setting
increased milliamperage (mA)
What component within the automatic exposure control (AEC) system is responsible for measuring the quantity of photons exiting the patient? -Rectifier bridge -Autotransformer -Exposure timer -Ionization chamber
ionization chamber
For additive pathology, the suggested adjustment is to increase what technique ________ and by how much ______%?
kVp by 5-15%
For destructive pathology, the suggested adjustment is to decrease what technique ________ and by how much ______%?
mAs by 25-50%
What is the primary purpose of an automatic exposure control (AEC) system? -Enhance image contrast -Increase radiographic spatial resolution -Automatically modulate the kilovoltage peak (kVp) -Maintain optimal receptor exposure
maintain optimal receptor exposure
For destructive pathologies, which factor should be decreased by 25-50%? -mas -kvp -density controls -SID
mas
Consider a technologist performing a lumbar spine series using an automatic exposure control (AEC) system. After acquiring the lateral radiograph, the technologist angles the beam to 5 degrees caudal and collimates to the area of the L5-S1 joint. How should the technologist change the technical parameters to ensure the same receptor exposure as the lateral view? -Increase kilovoltage peak (kVp) -Increase milliamperage (mA) -Decrease the source-to-image distance (SID) -No change is required
no change is required
Which specific factor does APR control? -mA -time -kvp -none of the above
none of the above because it controls all of these together
If kVp is adjusted with an AEC system, the radiographer will also need to adjust _____ to make the image diagnostic -mA -time -density -nothing
nothing because AEC compensates
When are the density controls used?
only used when density increase/decrease is desired for image quality (not to be used just because patient is larger/smaller than normal)
What does the backup timer prevent?
overdose of radiation to patient and tube from getting to warm
An important benefit of using an automatic exposure control (AEC) system is to minimize: -Patient dose -Patient motion -Image artifact -Heat accumulation in the tube
patient dose
Which of these could possibly be a contraindication against using AEC? -patient to large -patient unable to hold still -patient recently had contrast in their body -patient is very sick
patient recently had contrast in their body
What is the primary function of the back-up timer? -Prevent over-exposure to the receptor -Prevent over-exposure to the patient -Ensure adequate receptor exposure -Ensure adequate image contrast
prevent over-exposure to the patient
Changing the density settings to -1 will functionally do what? -reduce the mA of the exam -reduce the beam intensity by 50% -reduce the amount of exposure needed before the exam is turned off -make a darker image
reduce the amount of exposure needed before the exam is turned off
What will over collimating (light field to small, the active cell is cut off) do to an image when using AEC?
results in overexposure due to cell receiving too much exposure
What is minimum response time?
shortest exposure time that the system can produce -usually 0.001 seconds important because smaller patients/part thickness could have an even shorter exposure time so it will shut off once the time has been met.
In order to ensure optimal receptor exposure, which portion of the patient's anatomy should be positioned over the active automatic exposure control (AEC) chamber(s)? -Highest density structure -Lowest density structure -Structure of least concern -Structure of primary concern
structure of primary concern
Which of the following exposure factors is controlled by the automatic exposure control (AEC) system? -kilovoltage peak (kVp) -Milliamperage (mA) -Source-to-image distance (SID) -Time
time
If a PA chest is performed using AEC but the center cell is selected, how would you predict the image to appear? -to light -to dark -just right
to dark