Technical errors Flashcards
Processing artifacts are
98% of all film artifacts are produced in the processor or by manual processing
This is a review of the majority of the common problems
3 groups of artifacts on film
Equipment
Processing
Handling
X-ray tube malfunction
Collimator incorrectly positioned
Wrong area of interest
Too tightly collimated causing cut off of area of interest
Table malfunction
Grid cut off due to:
Incorrect distance
Incorrect positioning
Cassette issues
Front old or damaged
Dirt/debris inside the cassette
Warped cassette
Faulty latches
Foreign body on image can within what part of the machine
Within cassette
Within collimator
Between table and grid
Processor artifacts
Transport artifacts
Chemical artifacts
Sight development issues
Vertical streaks of alternating dark and light areas, as if some liquid ran down the film (which it did!)
The person processing the film did not use a time temperature chart and instead pulled the film out of the developer and held it up to the light to see if the film was black enough
The black streaks are where developer chemical was in contact with the film longer
Handling issues can cause
Dust on feed tray
Double exposure
Film fog – from, heat, age etc.
Scatter fog
Static
Sweaty fingerprints
Safelight fog and darkroom integrity
Patient artifacts
Motion
Artifacts on haircoat
Technical errors are caused by
Improper technique
kVp
mAs
Difference b/w conventional and computed/digital
The cassette containing intensifying screens and film is replaced by a reusable imaging plate (IP) or detector
Radiographic images are electronically captured, recorded and viewed at a computer terminal
The “wet” film processor is replaced with a computed imaging reader
After the digital radiographic image is made it is transferred to a computer for “image processing”
The image can then be adjusted as needed by the veterinarian
Computerized radiographic system is and consists of
CR was developed to retrofit existing radiographic machines
The basic CR system consists of:
Operator’s console with monitor or touch screen, barcode reader, keyboard and mouse
Variety of plates/cassettes
Plate reader
Conventional x-ray machine and table
Computed radiography steps
Enter patient information into the CR workstation
Create a study and ensure all necessary information is entered so the radiographs are legal
Perform erasure on plate(s) to be used
Select view and scan barcode of proper Imaging Plate (IP)
IP is placed in the bucky or on the table
Select proper factors
Make exposure
Insert IP into imaging reader
The image is processed onto a computer monitor
The IP is erased (flashed) so that it can be used again
After the digital radiographic image is made the image can be adjusted as needed by the veterinarian
Accept or reject image after evaluation
Complete study
Imaging plate works by
CR uses a PSP (phosphostimulable phosphor) detector screen, called an imaging plate
This type of screen absorbs and stores most of the x-ray energy, which is “read out” later
The PSP screens fit into a cassette that looks very similar to a conventional film-screen cassette; and is used identically to conventional screen-film cassette
Following exposure, the CR cassette is taken to a laser reader unit called an imaging reader
Here the latent image is processed
Image processing in CR after cassette placed in reader
The CR cassette is automatically opened and the CR plate is removed
As the CR plate moves through the processor, it is scanned by a laser beam
The laser light stimulates release of trapped x-ray energy stored in the plate as visible light
This released visible light is collected by fiber optics to a photomultiplier tube, producing an electrical signal
The electrical signal is digitized and stored on the computer
The CR plate is then exposed to a bright white light, erasing any residual latent image
The CR plate is returned to the cassette, ejected from the CR reader and ready to reuse
Things to note about the CR cassette
The latent image formed on CR cassettes is temporary, lasting for about 6-8 hours
Therefore, CR cassettes must be processed in a timely manner, preferably within a few minutes of exposure
Because of their sensitivity to secondary radiation, they must be stored carefully and should be erased (flashed) before use
This is essential if CR plates have not been used for 24 or more
Failure to do so will result in artifacts and reduced detail from background radiation
Scatter, primary beam, light leaks in the cassette or heat
Must tell the image reader what is on the imaging plate before you put it in the imaging reader
Image readers use a different processing algorithm for each different type of image
For example, a lateral tarsus will be processed differently than a DLPaMO metacarpal projection
CR is not faster than conventional processing
Both take about 90 sec to process an image but with conventional processing you can process more than one image during that time frame – CR you cannot*
You still need metal markers – putting them on electronically can make the images invalid in court
Advantages of CR
No wet processor or chemicals
Improved safety for staff
Better for environment
Short wait for images
The need for retakes is reduced
Images that are too light or dark that would be discarded on radiographic film can be adjusted with the computer software**
Images can be manipulated by computer programs for optimum viewing
They can also be drawn on, measured and annotated
Reduces radiation exposure**
Disadvantages of CR
Imaging plates are expensive so usually there are only a select few plates that are purchased
Larger plates have lower resistance
They wear out just like regular plates and need replacing
Often noticed by having ghost images on plate
Noise at low levels of radiation
Generally, below 60 kVp
Results in quantum mottle
Still have a processor that requires servicing
Can be a source of artifacts
Need to be flashed before each use due to susceptibility to scatter radiation
Digital radiography two types
Indirect digital imaging (CCD)
Direct digital imaging
Indirect digital imaging is
Abreviated CCD
Uses an IP that contains a thin-film transistor (TFT)
Converts radiation to an image that is imprinted on a camera, then transferred to a computer
Advantages and disadvantages of CCD
Advantages
More sensitive than film
Less expensive than direct digital imaging
Made up of components that can be serviced and replaced
Disadvantages:
An extra step for processing so can result in data loss
Direct digital radiography is
The conventional radiographic cassette and film are replaced with a digital imaging sensor
This imaging sensor is either permanently affixed to an x-ray table or attached to the DR computer via a cable or Wi-Fi
TFT that picks up the charge and transfers the radiation signal to the digital receptor
Limited by pixel size and how they are wired together
Advantages of DR
No processing time and immediate image acquisition
Only a few seconds between exposure and image
No imaging plate readers, cassettes, film, or processor and chemicals to hassle with
Excellent image quality
Image can be manipulated to optimize contrast and brightness
Edge enhancement
The computer identifies the edge of a structure
Disadvantages of DR
More expensive system
Imaging sensor very expensive to replace
Quality is limited by pixels and monitor
Dose creep
Poor technique charts from manufacturer
Hard to identify over exposure because computer fixes images
kV and mAs combine to produce
kV and mAs combine to produce dose
Every system handles the dose slightly differently
Best to use technique as close as possible to parameters of the animal being radiographed
Distance for radiographs causes
Distance is typically not a factor in small-animal imaging but is definitely a factor in large-animal imaging
Usually preset in small animal
The x-ray unit must be an exact distance from the detector every time for consistent results
Dose on radiographs does what
Once digital plate receives dose, computer uses histograms and algorithms to produce image
Plates require certain level of radiation to acquire image
Often means dosing high for smaller body part this issue improves as technology improves
Histograms
A histogram is a graphic display of an image and is displayed on the software of virtually every digital system
Algorithms
An algorithm is a formula or set of rules used in calculations or data processing
What is done right after a digital unit is purchased and installed
When a digital unit is purchased and installed, the service engineer who sets up the computers will establish the veterinarians preference, such as what level of contrast is acceptable in a chest and what density is preferred for abdomens and spines
Once the algorithms for that hospital are established, the service engineer can go into the computer from any location and correct any problems
Digital image processing
Spatial resolution and contrast resolution
Spatial resolution is expressed in line pairs per millimeter
Contrast resolution is expressed as the values of black and white
The descriptor for contrast resolution is dynamic range
The end result of digital imaging should logically be a high-resolution image
Limited by monitor output and pixel size
Contrast and brightness on DP
Contrast and brightness (windowing and leveling)
Windowing refers to the contrast range of densities
Leveling refers to density or brightness
Window level establishes the midpoint of the densities visible on the digital image
Dynamic range
Digital images take advantage of the ability of the digital process to create a greater number of shades of gray in the image
The human eye is not equipped to visualize and appreciate all these features; it is limited to 30 shades of gray
Hence, digital images look much better than film images
S-number is
used by Fuji, Philips, Konica Minolta
S-number or sensitivity number is the amount of luminescence emitted at 1mA at 80kVp and has a base value of 200
S-numbers are inversely proportional to exposure reaching the IP
S-numbers below the acceptable range indicate the IP was overexposed
S-number above the acceptable range indicate the IP was underexposed
S-numbers can be unpredictable because of the multiple variables involved in the algorithm*
Rules for s-number
S-numbers below 50% of the lower acceptance range MUST be repeated – there is a possibility that you burnt out a pathology
S-numbers above the upper acceptance range can be passed as long as quantum mottle is not present on the image
Digital imaging artifacts are caused by
Caused by the IP, grid, software or mechanical system
Identify the cause to correct
Most artifacts are human error
Most common artifact is quantum mottle
Picture archiving and communications system
Used by both CR and DR
It is the computerized organization and storage of the radiographic images
Must store the information in two places
All computers fail
