1. Radiographic Equipment
Stacy Kopso, M.Ed.,RT(R)(M)

2. Automatic Exposure Devices AEC or Phototiming
Control the amount of radiation reaching the image receptor by terminating the length of exposure
Determines the exposure time (therefore, total exposure)
Reproduce a desired amount of film density on images taken of selected body parts regardless of changes within the patients being examined
Designed to maintain consistent radiographic densities on images taken on wide variety of patients

3. Automatic Exposure Devices AEC or Phototiming
Advantage
Reproducibility
Radiographs taken on a mixed population of patients will fall within an acceptable or diagnostic range
Reduces repeats due to technical factors
Disadvantage
Improper positioning of central ray or bucky alignment
Incorrect photocell selection

4. Automatic Exposure Devices AEC or Phototiming
Items that impact the AEC at the control panel
kVp mA
Backup timer
Density selector
Photodetector (cell)
Items that impact the AEC at the x-ray table
Alignment of CR to part of interest
Alignment of bucky tray to CR Kv
Films exhibit an insufficient density due to under penetration
Control the contrast of the resultant image mA
Adjusts the “rate of exposure” delivered to photoreceptor
Adjust the “speed” or “length of time” for a given phototimed exposure
Backup timer
Determines the “Maximum risk” of exposure for a phototimed exam
Density
Used to correct/adjust for changes in body habitus for a give exam
Photoreceptor
Over/under exposures due to wrong selection or misplacement of body part over cell
Alignment of CR
Over/under exposure for sensitive exams (LS)
Alignment of bucky tray
Over/under exposure of area of interest

5. Automatic Exposure Devices AEC or Phototiming
Items that impact the AEC at the control panel
kVp mA
Backup timer
Density selector
Photodetector (cell)
Items that impact the AEC at the x-ray table
Alignment of CR to part of interest
Alignment of bucky tray to CR Kv
Films exhibit an insufficient density due to under penetration
Control the contrast of the resultant image mA
Adjusts the “rate of exposure” delivered to photoreceptor
Adjust the “speed” or “length of time” for a given phototimed exposure
Backup timer
Determines the “Maximum risk” of exposure for a phototimed exam
Density
Used to correct/adjust for changes in body habitus for a give exam
Photoreceptor
Over/under exposures due to wrong selection or misplacement of body part over cell
Alignment of CR
Over/under exposure for sensitive exams (LS)
Alignment of bucky tray
Over/under exposure of area of interest

6. kVp & mA Selector kV selector mA selector
Reduce dose (increase kVp, to decrease mAs)
Penetration
Contrast
mA selector
“rate of exposure”
Change “speed” or “length of time”

7. Backup Timer
Maximum length of time the x-ray exposure continues when using AEC
Safety measure for patient and tube
Set by radiographer or in unit
Maximum termination 600 mAs
Should be set at 150% to 200% of expected exposure time
Make be reached when you select table buck instead of upright bucky for a chest

8. Density Adjustment
The predetermined exposure level needed to terminate the timer is increased or decreased
Change rate of exposure
Increase or decrease the amount of radiation produced based on size of patient
+or-1=25%
+or-2=50%
When would we need to use the + or –
Pediatric if pt doesn’t extend out to the cells on a cxr
Hip xray if pts belly is big and you need to penetrate through to see head of femur
Routinely having to use this setting indicates a problem (AEC)

9. Radiation Detectors
Radiation is transmitted through the patient & converted into an electrical signal, terminating the exposure time
Over/under expose patient if wrong photocell is selected or patient is not positioned over cell
Predetermined level of radiation
AEC uses Ionization chambers or Phototimers
Sensors, chambers, cells or detectors
Detectors are the AEC devices that measure the amount of radiation transmitted.

11. Phototimer Phototimers Earlier generations
Use a fluorescent (light-producing) screeen and a device that converts the light to electricity
Photomultiplier tube
Electronic device that converts visible light energy into electrical energy
Photodiode
Solid-state device that converts visible light energy into electrical energy

12. Phototimer Exit device
Detectors are positioned behind the image receptor
Radiation must exit the image receptor before it is measured by the detectors
Light paddles coated with fluorescent material serve as detectors
The radiation interacts with paddles and produces light
Light is transmitted to PM tubes or photodiodes that then convert light into electricity
The timer is tripped and exposure is terminated

13. Phototimer

14. Ionization Chamber Most commonly used today
Cell that contains air and is connected to the timer circuit via electrical wire
Entrance device
Detector positioned in front of the image receptor
When chamber is exposed to radiation from a radiographic exposure, the air inside the chamber becomes ionized, creating an electrical charge
Charge travels along wire to timer circuit
Timer is tripped and exposure is terminated

15. Ionization Chamber

16. Minimum response time Minimum response time
Shortest exposure time that the system can produce
1ms
Increase the mA to decrease the exposure time(pediatric)
Make sure the minimum response time is not longer than the amount of time selected (overexposure)
Pediatric manual techniques

17. Manual Exposure
Exposure factors are determined by the size or thickness of the part under examination
Require the use of carefully constructed technique charts
APR
Anatomically programmed radiography
Table top x-rays

18. Quality Control AEC
When unit is first installed and at intervals thereafter
When there is a change in IR (CR to DR)
Consistent need to adjust density controls indicates that the AEC needs to be recalibrated
Use of phantoms to show consistent exposures to the image receptor for variations in technique factors, patient thickness and detector selection

19. Beam Restriction Devices
Aperture diaphragm
Lead plate w/ hole cut in middle that is slightly smaller than the image receptor size

20. Beam Restriction Devices
Cylinders and Cones
Attaches to the bottom of the collimator housing
Creates a circular shaped collimated field
Maximum beam restriction occurs w/an increased length and decreased diameter of cylinder or cone

21. Beam Restriction Devices
Variable Aperture Collimator
Controlled by radiographer
Permits adjustment of length & width of radiation light field
Utilized light-localization device to estimate the size and shape of field

22. Beam Restriction
Collimation- decrease in the size of the projected radiation field
Pt dose
decreases
Scatter radiation
Contrast
increases
Film density
Digital: Quantum noise
Increasing collimation & field size
decrease
Decreasing collimation &increasing field size
increase
An increase in field size has the opposite affect on all of the above