Midterm | AEC & Image Evaluation Flashcards
System used to consistently control the amount of radiation reaching the IR by terminating the length of exposure
Automatic exposure control (AEC)/ Automatic exposure detector
Two types of AEC systems (Radiation Detectors)
- Phototimers
- Ionization chambers
Use a fluorescent (light-producing) screen and a device that converts light into electricity.
Phototimers
An electronic device that converts visible light energy into electrical energy.
Photomultiplier tube
A solid-state device that converts visible light energy into electrical energy.
Photodiode
Phototimer AEC devices are considered as (1) devices because the detectors are positioned (2)
- exit-type
- behind the IR
Phototimer Mechanism
- Radiation interaction
- Light detection
- Signal generation
- Exposure control
Rad Light Si Ex
A hollow cell that contains air and is connected to the timer circuit via an electrical wire.
Ionization Chamber Systems
Ionization chamber AEC devices are considered to be (1) devices because the detectors are positioned (2)
- entrance-type
- in front of the IR
Ionization Chamber Systems aka
Cutie Pie Chamber Mechanism
Cutie Pie Chamber Mechanism
- Radiation interaction
- Ionization process
- Collection of charge
- Current generation
- Signal processing
RadIon CoCuSi
Where the actual amount of mAs used for that image is displayed immediately after the exposure, sometimes for only a few seconds.
mAs readout
AEC controls only the (1) of radiation reaching the IR and has no effect on other image characteristics such as (2)
- quantity
- contrast
Increasing the mA — exposure time to reach the predetermined amount of exposure
decreases
Maximum length of time for which the x-ray exposure will continue when using an AEC system.
Backup time
Serves as a safety mechanism when AEC is not used properly or is not functioning properly
Backup time
Provides a numerical value indicating the level of radiation exposure to the digital IR
Exposure indicator
Fuji and Konica
Exposure Indicator
Value= 1mR exposure
2x Exposure
1/2 Exposure
Exposure Indicator: Sensitivity (S)
Value= 1mR exposure: 200
2x Exposure: 100
1/2 Exposure: 400
Caresteam (Kodak)
Exposure Indicator
Value= 1mR exposure
2x Exposure
1/2 Exposure
Exposure Indicator: Exposure index (EI)
Value= 1mR exposure: 2000
2x Exposure: 2300
1/2 Exposure: 1700
Agfa
Exposure Indicator
Value= 1mR exposure
2x Exposure
1/2 Exposure
Exposure Indicator: log median value (lgM)
Value= 1mR exposure: 2.5
2x Exposure: 2.8
1/2 Exposure: 2.2
Term used in both digital and film-screen imaging to describe the variations in brightness and density.
Radiographic contrast or image contrast
In digital imaging, the number of different shades of gray that can be stored and displayed by a computer system is termed —
gray scale
The quality of a radiographic image depends on both the (1) and the (2) of the anatomic structural lines recorded (sharpness).
- visibility
- accuracy
The ability of a radiographic image to demonstrate sharp lines determines its quality
Spatial Resolution or Recorded Detail
Results from the radiographic misrepresentation of either the size (magnification) or the shape of the anatomic part.
Distortion
When the part is distorted, — is also reduced.
spatial resolution or recorded detail
Play important roles in minimizing the size distortion of the radiographic image
SID
OID
Shape distortion can radiographically appear in two different ways:
Elongation or foreshortening
Any misalignment of the central ray among these three factors alters the shape of the part recorded on the image
tube, part, or IR
Any unwanted image on a radiograph
Artifacts
Artifacts are detrimental to radiographs because they can make the visibility of (1), (2), or (3) difficult or impossible
- anatomy
- pathologic conditions
- patient identification information
Digital artifacts may be classified as (1) (CR plate, TFT array), occurring during (2) prior to the ADC or during the ADC process and subsequent (3) performed by the computer up to the point of (4).
- detectors
- image data extraction
- signal processing
- image display