w17 imaging errors and artifacts

define an image artifact and how its different from a FB

image artifact = any visible aspect of the image that is unrelated to the subject image, where an FB is related to the subject

describe what dropping a detector can do

disrupts electronics/circuitry or messes with the adhesion of the detector elements = missing image info

what are two ways a detector drop error appears on an image

speckling, horizontal lines

T or F: minor drop errors can be fixed via recalibration, but extreme errors require replacement

true

describe how detectors can become contaminated

fluid destroys the receptor

what does detector contamination via fluid look like

many vertical lines

what is a backscatter error + when does it occur

occurs when the collimation is wide or the exposure values are high (large pt), the photons penetrate the receptor, interact with the material behind the receptor, then scatter back to the detector

what does backscatter do to an image

able to see the detector electronics overlayed on the anatomy

corrective options to avoid backscatter

reduce field size, use lead shielding behind the receptor

T or F: detectors may develop defective detector elements over their lifetime

true

detectors may develop defective detector elements over their lifetime. how do we correct for this

use preprocessing which will interpolate signals from surrounding elements

define interpolation

the estimation of the signal based on the average of adjacent signals

what is image lag

when detectors retain aspects of a previous exposure overlayed on the current exposure

when does image lag commonly occur

when a low exposure occurs after a high exposure, or when exposures follow in rapid succession

another term for image lag

ghosting

describe why we do flatfielding exposures to calibrate detectors

corrects for the anode heel effect

T or F: when calibrations are performed, it’s important that the manufacturer’s recommendations are followed and that the imaging field is entirely clear of obstacles

true

T or F: processing errors can result from incorrect flatfield calibration

true

what happens when we perform calibration with the plate inside the bucky when it was supposed to be taken out

we will be able to see the ion chambers on our image

what does automatic shutter failure do to our image

we only see a sliver of the image

when does automatic shutter failure occur

when there is a lack of collimation, or when there is excessive scatter blurring the edges of collimation

how to correct for automatic shutter failure

re-shutter + reprocesses the image

T or F: to fix automatic shutter failure, we need to do a repeat

false; we can fix it in post-processing

when does values of interest error occur

the algorithm, includes the directly exposed region in the histogram processing = washed out structures. occurs when the exposure field is excessive

how to fix value of interest error

reprocess the image with the corrected value of interest field + re shutter to the desired region

T or F: imaging errors are usually due to technologist errors

true

why are secondary erasures important

CR receptors are sensitive to background information and will get radiation fog over time

what happens when the receptor is placed backwards in the bucky

the inner structure will be seen on the image

T or F: DR systems have a wide exposure latitude which is good, but gross exposure errors exceed the system’s ability to make corrections

true

describe clipping, an extreme example of detector saturation (ie what happens)

structures become completely absent from the image due to saturation error

how to correct for mottle

AEC

what is partitioning

splitting one receptor for multiple exposures and using lead to cover the unexposed regions. each one must have 4 sides of collimation

T or F: partitioning errors occur when there is an odd number of exposures per plate, as most digital receptors recognize even numbers of exposures

true

what does a partition error (odd number of exposures per plate) look like

washed out, low contrast

T or F: when AEC is selected and the collimation is not aligned, it may lead to overexposure errors and detector saturation artifacts

true

T or F: imaging artifacts can be debris attached to the receptor, glue that has dried onto the receptor, or debris within the collimator artifact

true