LRA-221 Week 2 Chapter 4 Review Flashcards
define artifact
- any undesirable densities on the processed image other than those caused by scatter radiation or fog
what are the 4 different types of artifacts?
- imaging plate artifacts
- plate reader artifacts
- image processing artifacts
- printer artifacts
define barcode layer
- allows the technologist to match the image information with the patient-identifying barcode on the examination request
what happens if the cassette was incorrectly oriented?
- the image will need to be rotated or flipped on the screen to display the image in correct anatomic orientation
define colored mark / sticker
- a label to indicate the appropriate orientation of the cassette in relation to the patient
define Bit depth
- the number of bits per pixel define the shade of each pixel
- 2^8 (8 is the bit depth. This means that there are 256 shades of gray. You would name this as “the pixel has a bit depth of 8”)
- number of photons detected within the pixel will determine the amount of gray level or bit depth within that pixel
define cassette
- is a durable, lightweight plastic material
- backed by a sheet of aluminum/lead that absorbs backscatter x-ray photons
- also contains an antistatic material (usually felt) to protect against static electricity back up, dust collection, and mechanical damage to the plate
- very similar to a conventional cassette
define collimation
- the reduction of the area of beam that reaches the patient through the use of two pairs of lead shutters (that are encased in a housing attached to the x-ray tube)
- results in an increased contrast resolution due to the reduction of scatter
define fast scan direction
- the movement of the laser across the imaging plate
- also known as the “scan”
define focused grid
- lead strips angled to coincide with the divergence of the X-ray beam and must be used within specific distances using a precisely centered beam.
- because they’re angled, we need to worry more about centering the patient properly
define grid frequency
- the number of grid lines per centimeter or lines per inch.
- The higher the frequency or the more lines per inch, the finer the grid lines in the image and the less they interfere with the image.
- The higher-frequency grids require more X-ray photons to produce an image than lower-frequency grids require, and therefore the patient will receive a higher dose.
define grid ratio
- The relationship between the height of the lead strips and the space between the lead strips
- The higher the ratio, the more scatter radiation is absorbed
define imaging plate
- a thin sheet of plastic
- consists of several layers
what are the 7 layers of the imaging plate?
- protective layer
- phosphor layer (active layer)
- reflective layer
- conductive layer
- color layer
- supporting layer
- backing layer
define kilovoltage peak
- also known as kVp
- penetration
- quality of photons
- range from 45-120 in most digital systems
define laser
- light amplification of stimulated emission of radiation, is a device that creates and amplifies a narrow, intense beam of coherent light
- requires a constant power source to prevent output fluctuations
define milliamperage seconds
- also known as mAs
- the quantity of photons
define moire
- wavy artifact
- which occurs because the grid lines and the scanning laser are parallel
define phosphor center
- area of the crystal
- when remnant beams interact with electrons in the barium fluorohalide crystals, giving energy to the electrons in the crystal
define photodetector
- amplifies the light and sends it to an ADC.\
- absorbs lines of light intensity information that occurs from translation
define translation
- the movement through the scanner
- moves in a parallel manner at a certain rate through the reader
define quantum mottle
- grainy image
- this occurs when insufficient light is produced
define quantum noise
- grainy image
- this occurs when insufficient light is produced
define shuttering
- postexposure image manipulation
- black background can be added around the original collimation edges, virtually eliminating the distracting white or clear areas
define slow scan direction
- the movement of the imaging plate through the reader (also known as the “translation” or “subscan direction”).
define protective layer
- a very thin, tough, clear plastic that protects the phosphor layer.
define phosphor layer
- also known as the active layer
- a layer of photostimulable phosphor that “traps” electrons during exposure
- may also contain a dye that differentially absorbs the stimulating light to minimize the light spread as much as possible
define photostimulable phosphor
- also known as PSP
- is made up of barium fluorohalide
define reflective layer
- sends light in a forward direction when released in the cassette reader
- This layer may be black to reduce the spread of stimulating light and the escape of emitted light
- Some detail is lost in this process.
define conductive layer
- material that absorbs and reduces static electricity.
define color layer
- absorbs the stimulating light but reflects emitted light.
define support layer
- gives the imaging sheet some strength.
define backing layer
- soft polymer that protects the back of the cassette.
how does cassette PSP differ from conventional radiograpy?
- PSP uses a cassette that is simply a lightproof container that protects an imaging plate from light and handling
how is exposure recorded in a cassette system?
- the remnant beam interacts with electrons in the barium fluorohalide crystals contained within the imaging plate
how long does that interaction between the photon and the imaging plate remain?
- it’s never lost
- can take hours, days
- a certain amount of exposure will still be left over in the imaging plate
what 2 type of PSP readers are there?
- line scan
- point scan
what’s the difference between point scan and line scan?
- point scan only uses one single laser point to hit the imaging plate
- line scan uses multiple laser points
true or false: Surfaces at both ends of the laser container reflect energy back and forth as atoms bombard each other, stimulating the lower-energy atoms to emit secondary photons in the same frequency as the bombarding atoms
true
true or false: When the energy builds sufficiently, the atoms discharge simultaneously as a burst of coherent light; it is coherent because all of the photons are traveling in the same direction at the same frequency
true
what’s another name for computed radiography?
CR
is CR related to conventional radiography?
- yes, the materials and process that needs to be done is similar
what’s the difference between CR and conventional radiography?
- CR uses a cassette and a reader
- creates a latent image that needs to be processed (must be digitized so we can interpret it)
define PSP
- captures/creates the latent image
made up of extremely small particles which store and releases energy - captures x-ray photons to create latent image
- commonly made up of barium fluorohalide
define photelectric absorbtion
- x-ray photons that are capture in the PSP layer by energy transfer process
define latent image
- made up of trapped energy from interaction between x-ray photons and phosphor atoms
- not visible to us (needs to be processed)
where is the imaging plate inserted after to get digitized?
- reader
what do plate readers use to convert stored energy into light photons?
- laser
true or false: the imaging plate should be processed as close to the time as possible to avoid any loss from the latent image
true
what are the different components to an imaging plate?
- laser
- splitter
- focusing lens
- mirror
- photomultiplier tube (or charged coupled device (CCD))
- analog -to-digital converter
define analong-to-digital converter
changes the latent image into a digital image, allowing us to see/interpret the radiograph
define raster
a zig zag pattern
name the process of an image being processed
- the imaging plate is extracted with rollers
- the laser is activated, going through the splitter or laser separator
- the laser hits the reference detector (monitoring the intensity of the laser
- after hitting the splitter, laser hits the focusing lens
- the laser hits the mirror, reflecting to hit the imaging plate
- with a raster pattern, the image releases light photons
- light photons are collected by the photomultiplier tube
- photomultiplier collects the light photons, making them brighter
- light photons go through the ADC
- digital image is made for interpretation
define CCD
- charged coupled device
- amplifies light photons
- convert light photons into an electrical signal
what happens after process is done?
- a complete erasure of the image is done
- this is done by using intense white light to erase the image
- depending on the body part, it may take some time to fully erase the image
what is the laser made up of?
- helium
- solid state laser diodes (recent use)
what color of laser is used to scan the imaging plate?
- red light
- done in a raster pattern
- gives energy to the trapped electrons
- the laser scans across the imaging plate multiple times
true or false: the beam is “shaped” by special optics that keep the beam size, shape, and speed largely independent of the beam position
true
what’s the typical throughput in cassettes?
- 50 cassettes per hour
define digitizing an image
- assigning a numerical value to each light photon
- digitization
define analog
- a device or system that represents changing values as continuously variable physical quantities
- Ex.) a watch
define matrix
- group of squares that make up the image information.
define pixels
- a square
- also known as picture element
with an increase in pixels, we get-
an increase of spatial resolution
true or false: The image is digitized both by position (spatial location) and by intensity (gray level
true
define spatial resolution
amount of detail present in any image
what determines resolution in PSP?
- phosphor layer thickness and pixel size
true or false: imaging plates are extremely sensitive to scatter radiation and should be erased to prevent a buildup of background signal
true
define erase cycle
a cycle used to remove background radiation and scatter in an imaging plate
true or false: it is imperative that cassettes are kept apart so that the technologist knows which cassette goes with which body part.
true
what happens to the image if the wrong body part is selected?
- the image may be processed incorrectly and fail to display properly
- the result can be either too dark or too light.
- can also appear grainy or seen as underexposed
what is the result of improper menu selections?
- may lead to overexposure of the patient and repeated exposures
true or false: It is vital that the proper balance between patient dose and part penetration be achieved.
true
what’s the difference between conventional radiography and digital?
- digital no longer depends on kVp ????
what are the 2 types of imaging plates?
- standard and high resolution
define high resolution imaging plate?
- contains a thinner phosphor layer as compared to the standard plates
- the thinner layer results in greater image sharpness (spatial resolution)
what exams uses smaller cassette sizes?
- extremities
- mammography
- etc.
why do PSP’s need to use grids?
- because they are more sensitive to low levels of radiation
what are the 3 factors of grid ratio
- frequency
- ratio
- focus
true or false: The higher-frequency grids require more X-ray photons to produce an image than lower-frequency grids require, and therefore the patient will receive a higher dose.
true
what are the 2 types of grids?
- parallel and focused
true or false: When exposing a patient, the larger the volume of tissue being irradiated, the more scatter will be produced.
true
true or false: we strongly advise that conventional lead markers be used in the same way they are used in film/screen systems
true
- this gives us credibility that we performed our job properly
define imaging plate artifacts
- cracks in the imaging plate
- static due to low humidity -> hair can cling to imaging plate
- backscatter can cause dark line artifactsd
define backscatter
- created by X-ray photons transmitted through the back of the cassette can cause dark line artifacts.
define image processing artifacts
- can happen from choosing the incorrect processing parameter for a particular body part or incorrect sampling of the image file
define plate reader artifacts
- intermittent appearance of extraneous line patterns
- White lines that are parallel to the direction of plate travel are caused by dirt, dust, or scratches on the light guide
- Insufficient erasure after an overexposure (may result in residual image information being left in the imaging plate before the next exposure)
define printer artifacts
- Fine white lines may appear on the image because of debris on the mirror in the laser printer.
name some operator errors
- insufficient collimation
- using the backside of the cassette instead of the front
- underexposure, overexposure
- not removing clothing
