artefacts in CR and DR

Artifacts in CR and DR:

MODERATOR:

PRESENTOR:

PRAVEEN KUMAR M

Definition:

Artifacts are any undesirable objects or structures recorded on the radiograph

Computed Radiography (CR) system

• CR Imaging Plate (IP)
• -Life is around 10000 exposures
• -Very sensitive to scattered radiation
• -The dynamic range is lower than DR

-The DQE is lower than DR

X-ray unit

• Image plates
• CR reader

CR workstation

Structure of the Imaging Plate

• There have different layers for different function
• Protective layer -Insulates IP from handling trauma
• Phosphor layer -Holds the photostimulable phosphor (PSP)
• Support layer made of polyester-The base on which the other layers are coated
• Conductor layer -Grounds the IP eliminating electrostatic problems

Light shield layer -Prevents light from erasing data on the IP

Computed radiography Image acquisition Image plate cycle:

• 1.When the exposure is taking, latent image will create in the image plate

2.CR reader will extract the latent image from the image plate 3.After readout the image, the image plate will erase the residual signal by the erasing light. And the plate can reuse again.

1.The cassette is opened in the CR reader with release of the imaging plate from the cassette

2.The image plate is moved by the rollers for scanning by the laser beam 3.The laser light stimulates the trapped electrons to become free and release of light photons 4.The light released from the imaging plate is collected by the fiber-optic light guide and strikes a photomultiplier tube (PMT) where it produces an electronic signal 5.The electronic signal is digitized and stored in a display monitor 6.The image plate is then exposed to a high-intensity halogen lamp which erases any residual energy remaining from a prior exposure 7.The image plate is returned to the cassette which is ready for reuse

CR artifacts are broadly classified into

• 1.Image acquisition artifacts

2.Image processing artifacts

1.Image acquisition artifacts

• 1.Twin Artifacts (Double Exposure)
• 2.Uncollimated Images
• 3.Delayed Scanning
• 4.Exposure Though the Back of the Cassette
• 5.Inappropriate Exposure Factors
• 6.Improper grid usage
• 7.Scatter Radiation
• 8.Care and Carelessness

9.Light Bulb Effect

Twin artifact (Double Exposure)

Postprocedure radiography of KUB with double-J stent shows two double-J stents (arrows) resulting from double exposure, one during inspiration and other during expiration.

Repeat radiography taken to reconfirm shows single double-J (arrows)

Chest radiography show double exposure due to IP unloading

Causes

• -Two subsequent exposure on same imaging plate
• Appearance
• -Duplication of images
• Remedy

-Proper knowledge of using of X-ray equipment

Uncollimated images :

Uncollimated image resulting from lack of primary beam collimation. Radiograph of pelvis shows increased density over midportion and to right side of pelvis because of improper collimation.

Subsequent pelvis radiograph with proper collimation shows uniform density over pelvis.

Causes

• -Improper collimation
• Appearance
• -Unsharp images
• Remedy

-Proper collimation in accordance with cassette size and body part

Delayed Scanning:

Neck radiographs was subject to delayed readout (after 48 hours).

It show decreased density in periphery as compared with center of images, as fading of image starts from periphery (arrows)

Abdomen radiographs was also subject to delayed readout.

It show decreased subject contrast

Causes

• -Delayed between acquisition and processing of image
• Appearance
• -Fading of image

Remedy

-Proper knowledge of radiographers to check that no delay occurs between acquisition and processing.

Exposure through the Back of the Cassette

Radiograph of neck shows rounded radiopaque ring shadow (arrow) on the right lower part of the neck, which if overlooked, can be wrongly diagnosed as tracheostomy tube

This axillary shoulder was exposed through the back of a cassette.

A different pattern to the prevision radiography because of different design of the cassette.

Causes

• -Poor basic knowledge of construction of cassettes
• Appearance
• -Various patterns of image according to cassette design
• Remedy

-Proper education of radiographers in handling of cassettes

Inapropriate exposure factors

• Overexposure
• Radiograph of hands shows darkening of image that obscures image details.
• Artifact is result of overexposure.

It occurs over the latitude of the image plate

Causes

• -Improper exposure setting
• Appearance
• -Darkening of image
• Remedy

-Proper exposure factors to be used based on body part and patient size

Inapropriate exposure factor underexposure

Image shows underexposed grainy radiograph of KUB in which quantum mottle is evident and image quality is degraded

Control radiograph of same patient as in previous slide using proper exposure factors.

Underexposure

Lumbar spine image shows underexposed in which very noise of the whole image and the diagnostic value also decrease.

Causes

• -Improper exposure setting
• Appearance
• -Grainy image owing to quantum mottle
• Remedy

-Knowledge of dynamic range and its limitation in CR system

Improper Grid usage: Moire Pattern

Radiograph of pelvis shows wavy radiolucent lines, resulting in suboptimal image, that were caused by usage of grid with frequency of 33 lines/cm.

artefacts in CR and DR

Moiré patterns can easily be caused by low frequency grids in a digital image, because of the very high contrast signal that the grid strips project onto the detector

artefacts in CR and DR

The moire pattern seen in this knee image was caused by using a grid with a frequency of 33 lines/cm, which was oriented with the grid lines parallel to the plate reader's scan lines.

Causes

• -Usage of grids with low grid frequencies
• Appearance
• -Different types of moire pattern

Remedy

-Usage of grids with 60 lines/cm or more; grid lines should run perpendicular to plate reader’s laser scan lines

Scatter Radiation

• Cassette was kept accidentally in radiograph with pen over it for some time.

Radiograph of abdomen shows fading of image of pen overly lumbar spine.

No erasure of long storage Image plate.

The image plate had put in the examination room for a long period without used.

Causes

• -Cassette placed in too close the primary beam or no erasure of long storage Image plate
• Appearance
• -Deterioration of quality of image and imprints of objects placed over cassette.
• Remedy

-Protect cassette from any unwanted radiation and erase cassette before using

Care and Carelessness

Kink artifact due to bucking of imaging plate.

IVU radiograph shows curvilinear marks (arrows) adjacement to right upper and lower pole of right kidney, which can misdignosis of contrast extravasations.

Other kink marks are seen in course of left ureter, which can be mistaken for calcified stone.

Causes

• -Mishandling of imaging plate during cleaning process
• Appearance
• -Kink marks on the image
• Remedy

-Cassettes and image plates should be handled with care

Light bulb effect

Chest radiographs show darkening (arrows) in lower and outer portions of radiograph, obscuring details of image.

Darkening occurs because of either high kV used in obese patients, scatter radiation or improper collimation.

The light bulb effect most occur in chest radiography for the obese patient

Causes

-High exposure, back scattered radiation entering imaging plate from patient’s bed due to increased exposure for obese patients or due to uncollimated x-ray Appearance

• -Darkening of lower and outer portions of an image
• Remedy

-Reduce back scatter by lowering the KV or proper collimation.

2.Image Processing Artifacts

• Hardware induced artifacts
• Image plate:
• Artifacts due to cracks on imaging plate
• Artifacts due to dust particles on imaging plate
• Roller artifacts:
• Disparity artifact
• Damage of imaging plate due to rollers
• Dust over rollers
• Malfunctioning rollers
• Plate reader artifact
• Cassette-related artifact
• Software induced artifacts
• Image transmission errors
• Communication error artifact
• Data cable malfunctioning artifact

Artifact due to improper erasure setting

Hardware induced artifacts

Artifacts due to cracks on imaging plate Chest radiograph shows curvilinear opacity overlying left clavicle (arrow), which suggests cracks due to mechanical stress.

Opacity can be misdiagnosed as parasitic calcification.

Thumb radiograph showing cracks (white arrow) that usually first become visible on the IP edges.

As deterioration progresses, cracks appear closer to the clinically used areas of the IP (black arrow).

In some instances, early cracking along the edge of the IP does not occur.

This crack appears as a lucency near the radius, which could be confused with a foreign body..

Causes

• -Damaged imaging plates during frequent transportation
• Appearance
• -Cracks
• Remedy

-Change imaging plate

Artifacts due to dust particles on image plate

Radiographs of right elbow joint show radiopacities (arrows) overlying soft tissues, which like soft-tissue calcification or foreign bodies but are actually due to dust over imaging plate.

left thigh show radiopacities (arrows) overlying soft tissues

Causes

• -Dust particles wedged over imaging plate
• Appearance
• -Focal radiopacities
• Remedy

-Regular cleaning of imaging plates with proper cleaner (ethyl alcohol).

-Paper towels or gauze should not be used because they leave fibers on the plate, the use of lint-free cloth is advisable.

Disparity artifact

This artifact occurs because of malfunction of roller in CR reader,causing defective scanning and resulting in alteration in image contrast (arrows) in upper and lower half of chest radiograph.

Lower half of it was exposed to laser beam for longer time, which resulted in brighter image output that suboptimal image

Causes

• -Malfunctioning of rollers in CR reader
• Appearance
• -Defective scanning resulting in alteration in image contrast
• Remedy

-Periodic cleaning of roller in CR reader

Damage of imaging plate due to rollers

• Chest radiograph shows radiopacities (arrows) along right lateral chest wall.

One can easily misdiagnose opacities as calcified granulomas in lung.

Causes

• -Mechanical damaging of IP during transport through rollers
• Appearance
• -Focal linear radiopacities
• Remedy

-Replace that part of roller

Dust over rollers :

Radiograph of pelvis shows horizontal radiopaque line (arrows) that can be traced outside margins of pelvis

artefacts in CR and DR

Chest radiograph shows multiple scattered radiopacities (white arrows) overlying soft tissues of left upper abdomen due to dirt over localized area on rollers.

These can be misdiagnosed as soft-tissue calcification. There is another radiopacity (black arrow) look like a gallstone in right upper of the abdomen, which is actually caused by roller damage

Causes

• -Dust deposited over IP during transport through rollers
• Appearance
• -Multiple localized radiopacities
• Remedy

-periodic monitoring the CR reader periodly

Malfunctioning rollers

Anterior half of lateral skull radiograph is not visualized because slipping of feed rollers, resulting image being half read (black arrow).

Radiopaque line (white arrow) is plate reader artifact resulting from dirt in the light guide.

Causes

• -Slipping of feed rollers from transport
• Appearance
• -Half-read image
• Remedy

-Periodic cleaning and recalibration of feed rollers

Plate reader artifact

The horizontal white line (arrow) shown on this chest radiograph was caused by dirt on the light guide in the plate reader.

The light guide collects light emitted from the imaging plate when it is scanned by the laser.

Lateral knee radiograph shows horizontal thin radiopaque line (arrow) overlying supracondylar region.

Artifact is attributed to dirt in light guide in CR reader.

Lateral shoulder radiograph shows vertical thin radiopaque line (arrow) overlying scapular region.

Chest radiograph shows vertical radiopaque line (arrow) cross the right lung region.

It is a common artifact occur in CR system

Causes

• -Dirt over light guide
• Appearance
• -Linear radiopaque line
• Remedy

-Periodic cleaning of light guide by supplier.

-For the A&E shift, sometimes we have not enough time to wait the supplier technical staff to clean the light guide.

-We may do it by ourselves.

Cassette related Artifact:

The dark line along the lateral portion of this upper abdomen is caused by backscatter transmitted through the back of the cassette.

The line corresponds to the cassette hinge where the lead coating was weakened or cracked.

artefacts in CR and DR

Vertical linear radiolucent line (white arrows) seen over head of first metacarpal simulates linear fracture (black arrow) unless traced beyond margins of bone.

Artifact is cause by cracks in lead foil in the back of cassette.

Causes

• -Cracked or weakened lead coating on back of cassette
• Appearance
• -Linear radiolucent line
• Remedy

-Replace of cassette

Software Induced Artifacts

Communication error artifact

Lower part of radiograph (arrow) of knee joint was not visualized because of missing lines of pixels.

Trasmission of image was truncated because of sudden power failure

Causes

• -Power failure during image transmission
• Appearance
• -Missing line or pixels in resulting image

Remedy

-Do not process the IP during electric supply check and the power supply should connect to essential socket

Data cable malfunctioning artifact

Lateral view of lumbar spine radiograph shows alternating radiopaque and radiolucent line obscuring image detail.

Problem was narrowed down to malfunctioning data cable in CR reader.

Causes

• -Failure of data cables in the power unit of CR reader
• Appearance
• -Alternating radiopaque and radiolucent lines
• Remedy

-Replace data cables

Artifact due to improper erasure setting

KUB radiograph shows superimposed residual chest radiograph image, which is seen in form of ribs and clavicle shadows (black arrows).

• Also note two side marker (white arrows) in the radiograph.

Artifact was due to improper erasure setting for the chest radiograph.

This bilateral knee image was spoiled when the incorrect erasure setting was used to eliminate a previous femur image.

Evidence of this is the residual image of the lead marker in the top corner of the image, the tissue line from the previous image (upper arrow) and the additional line of collimation along the bottom of the image (lower arrow).

Causes

• -Malfunctioning of the erasure light
• Appearance
• -Residual image is left in IP
• Remedy

-Replace the erasure light

Artifact of dry Laser Printer

The chest radiograph shows a radiopaque line in the central region, it is not the imaging plate artifact or plate reader artifact because the artifact only appear in the film, but not in the monitor image.

And for the solve this artifact.

We can clean the printer head of the printer which may has some dusts in the printer head.

Direct Digital Radiography (DDR)

Flat-panel detector (~70% cost of system) Photoconductor (most commonly is selenium) convert x-ray photons into electrical charges by setting electron free The dynamic range is wider than CR

The DQE is higher than CR

1.Is a cassette-less system

• 2.Use a flat panel detector.
• 3.Detector provides direct digital output
• 4.No processor and reader required
• 5.Images available in below 10 seconds

6.Need new equipment installation

Computer processing

• Establish location of collimated
• Define anatomic region
• A histogram is generated by dividing a scanned area into pixel and determining the signal for each pixel
• Produce look-up table based on histogram from anatomical area
• Final display image

Noisy Detector Power supply

Vertical lines, which are symmetrical around the center of the image, are caused by a moisy detector power supply Solution:

-Replace power supply

Vertical lines, which are symmetrical around the center of the image, are caused by a noisy detector power supply

Solution: Replace power supply

Tomo Bar Artifact

• This artifact is caused by a bad pixel
• Solution:

-Perform detector bad pixel calibration to map out the bad pixel

Fibre Optic Cable malfunction

• Dots or vertical lines in the image can be caused by a bad optic cable.

Solution: Replace fibre optic cable.

Latent Image

• Latent image which is caused by over exposure.
• Solution:

-Wait and the latent image will disappear.

Loose Cone

• Cone has fallen out of the x-ray tube port and is blocking the collimator from opening.
• Solution:

-Remove the collimator and re-attach the cone to the tube port

Bar code artifact

• Bar code artifact can be caused by a failure in a data module or the detector
• Solution:

-Perform bad pixel calibration, if calibration fail then replace detector

Bar artifact

• Bar artifact can be caused by a failure in a data module

Solution: Replace detector

References:

Christensen’s physics of diagnostic radio;ogy, thomas s curry, james, E downey, 4th edition.

Shetty C M et al. AJR (2011). Computed Radiography Image Artifact Revisited.

L j Cesar, B A Schueler, F E Zink, T R Daly, J P Taubel and L L Jorgenson, BJR (2001). Artefact found in computed radiography.

Korner, M., Weber, C. H., Wirth, S., Pfeifer, K. F., Reiser, M. F. & Treitl, M. (2007). Advances in Digital Radiography: Physical Principles and System Overview. Radiographics.

Oakley, J. (2006). Digital Imaging – A Primer for Radiographers, Radiologists and Health Care Professionals. United Kingdom: Cambridge University.