Image Receptors Flashcards
An image receptor is:
a medium that transforms the x-ray or useful beam into visible image.
Useful beam:
x-rays emerging from tube.
Remnant beam:
x-rays that remain after the useful beam exits pt. (scatter & image forming x-rays)
Image forming X-rays:
X-rays that form the radiographic image by interacting with IR. Also known as Remnant Radiation or Exit Radiation.
Three types of Image Receptors:
- Film with Intensifying Screens
- Imaging plates (CR)
- Flat panel detectors (DR)
Film:
film cassette contains an intensifying screen which turns energy from x-ray into visible light to expose film
Latent image:
invisible image before it is processed into an image we can see.
Manifest image:
image after it has been processed so that we are able to see it.
CR (Computed Radiography):
uses loaded cassette consisting of imaging plate containing photostimulable phosphor (PSP).
DR (Direct Readout digital radiography):
utilizes flat panel of detectors to absorb exit radiation.
Neither CR or DR utilize:
film.
How are CR IR’s similar to film?
the IR can be used similar to a film cassette – in the Bucky, on the tabletop or in a mobile unit.
The CR does not contain a screen, but rather a/n:
Imaging plate.
Characteristics of Direct Exposure Film (non-screen film):
used without intensifying screen
single emulsion thicker than screen film
longer developing time
greater exposure
manual processing needed since emulsion is so thick
Why is direct exposure film not used frequently in medical imaging?
Exposure is too great to the patient.
What areas is direct exposure film used in?
Dental
reconstructive surgery of hand,
biopsy specimen
forensic
What is the most widely used type of film?
Screen film
Characteristics of screen film:
used with one or two intensifying screens more sensitive to light less sensitive to x-rays thinner emulsion/less development time less x-ray exposure manual or automatic process single or double emulsion
What are the three characteristics of film to keep in mind?
Contrast
Latitude
Speed
Contrast is inversely proportional to:
it’s exposure latitude.
What is exposure latitude?
the range of exposure factors that will reproduce an acceptable radiograph.
What kind of exposure latitude does a high kVp have? (90-120 kVp)
A high kVp has more latitude (or more margin for error).
What kind of exposure latitude does a low kVp have? (50-80 kVp)
A low kVp has less latitude (or less margin for error).
What does “speed” mean in reference to film?
the degree to which the emulsion is sensitive to x-rays or light OR the ability of an emulsion to respond to radiation such as light and x rays.
The greater the speed of film:
the more sensitive it is and the less exposure necessary to produce density on film.
Factors affecting speed:
Number of silver halide crystals
size of silver halide crystals.
How is film speed and sensitivity influenced by size and number of halide crystals?
As the number of halide crystals and size of the crystals increase, the speed and sensitivity of film increases.
How does film speed affect exposure?
the faster the speed of film the less radiation exposure needed to produce a specific density AND
the faster the speed of film the less radiation dose to the patient
Speed/mAs conversion formula:
Used to determine how to compensate or adjust mAs when changing from fast system to slow system or vice versa
mAs1 = IR speed2
mAs2 = IR speed1
What exams would one use a fast speed system for?
Thorax Abdomen Pelvis Skull Contrast media
What exams would one use a slow speed system for?
Extremities, mandible, nasal bones
Detail or extremity systems are slower and require ___________, which results in _________, and produces _______ recorded detail.
greater exposure rates, greater pt dose, excellent.
Increased speed allows a radiographer to:
reduce x-ray exposure to pt and still be able to produce an image with the necessary amount of density to produce a diagnostic image
