Transcript Digital Artifacts

QC/PACS Artifact
Identification
Artifact Causes
• Image receptor/Hardware
– Dirty
– Foreign material
– Failures
• Software
– Algorithm
– Enhancements/manipulations
• Operator/Patient
– Collimation
– Misused equipment
– Incorrect patient data entry
Image Receptor/Hardware
• Dirt
– In the CR cassette or reader
• Foreign material
– Matter other than dirt within the CR cassette
or reader
• Failures
– Dead pixels
– Mechanical failures with in the CR reader
– Within the PACS network
CR Screen Artifacts
These are caused by
Dirt or other foreign
matter within the cassette/plate
apparatus
Dead Pixels
• Calibration algorithms detect
individual pixels, clusters, and
lines of contiguous pixels that
fail to produce a usable output
value. Algorithms are applied
to the image to determine pixel
values for the ‘dead’ or missing
pixels.
CR Ghost Images
Ghost or memory artifacts occur when the radiation
remains trapped in the phosphor plate. Remember,
radiation can remain trapped for several minutes. CR
plates must be correctly erased to prevent ghost images.
Ghost Image
• This artifact can also
occur with DR
systems; particularly
systems using
photodiodes.
• The artifact occurs
when exposures are
made too rapidly and
the unit was unable to
clear its data
completely.
CR Reader Artifacts
• Typically display as
lines across the
entire image
– In contrast to dirt
within the cassette
or on the PSP
which are shorter
and/or curved lines.
Damaged laser beam
head
Transmission errors in
the network
Printer Distortion
• Occurs when the image size and the
printed size are not equal.
Software Causes
• Algorithms
– Incorrect selection
– Age related
– Pathology induced
• Post-processing
– Edge enhancement, etc
Edge Enhancement
•
High contrast and edge definition
– Lose fine detail on the edges of high contrast areas
For the pediatric chest an adult chest algorithm was selected.
Technologist error.
DR - RF Noise
Operator Errors
•
•
•
•
Collimation
Backscatter
Moire artifact
Quantum mottle
– Insufficient mAs
Collimation
• Too much or too little
collimation may effect
image quality. When
being reconstructed the
image histogram has
been programmed to
search for a particular
collimation pattern. If the
collimation is faulty it may
result in artifacts on the
final image.
Light bulb Artifact
Image A demonstrates backscatter on the image which produces a ‘light bulb’
effect within the image. Image B shows the same image with less kVp.
Moire Pattern
Grid lines run in the same direction as
the laser in the CR reader.
Quantum Mottle
Image A demonstrates quantum mottle resulting from too few photons striking the
imaging plate. Images B and C show increasing mAs values and decreasing
quantum mottle.
Conclusion
• Digital artifacts can be caused by
numerous means.
• It is the responsibility of the II/PACS
professional to be the final monitor of
image quality within the modern imaging
department.
Future Possibilities
Digital image monitoring