Computed Radiography Image Artifacts

• Computed radiography (CR) systems based on photostimulable phosphor (PSP) image detectors (i.e., imaging plates) were first introduced commercially in 1983.

• Widely accepatable since they are cost-effective, particularly suitable for bedside radiographic examinations in emergency conditions

ADVANTAGES OVER DR• The image quality of CR on large body parts,

such as the chest and abdomen, is better than that of digital radiography.

• Advantage of positioning flexibility for difficult views, because CR cassettes can be placed in any position.

• A multiple cassette size option is available.• A significant role in an emergency setup.• After performing cost analysis and capacity

utilization of general radiography, CR still scores over DR

Workflow of CR Systems CR Readout Process

• Image acquisition is made using a PSP-based plate made of barium fluorohalide; enclosed in a cassette

• The plate is exposed to x-rays using standard radiographic equipment.

• During the exposure, electrons in the phosphor plate are excited to a higher energy state; these excited electrons are trapped and form a latent image which is then processed & retrieved in CR reader

Processing of Image

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

• STEP 2 :- The imaging plate is moved by the rollers for scanning by the laser beam.

• STEP 3 :- The laser light stimulates the trapped electrons to become free and return to a lower energy state, which results in the release of light photons.

• Now, the two lights (laser light and the released light photon) have different wavelengths, which forms the basis for image retrieval.

• And the photomultiplier tube (PMT) identifies these higher energy and shorter wavelength light photons

• STEP 4 :- Light released from the imaging plate is collected by the fiber-optic light guide and strikes a PMT, where it produces an electronic signal.

• STEP 5 :- The electronic signal is digitized and stored in a display monitor and later sent to a PACS.

• STEP 6 :- The image plate is then exposed to a high-intensity halogen lamp, which erases any residual energy remaining from a prior exposure.

• STEP 7 :- The image plate is returned to the cassette, which is ready for reuse.

ARTIFACTS:AN UNWANTED DENSITY

ON THE FILM

Artifacts

• Any irregularity on an image that is not caused by proper shadowing of tissue by the primary x-ray beam.

• Are undesirable optical densities or blemishes on a radiograph.

• Can be very interesting at times. You become the detective, what caused that?

Image Acquisition Artifacts:

• Operator Errors

Twin Artifacts (Double Exposure)• Causes :- Two subsequent exposures on

same imaging plate or double exposure.

Lead to errors in interpreting the position of line and catheters

• Appearance :- Duplication of images

• Remedy :- Proper knowledge of the usage of x-ray equipment

A, double-J stent was placed on left side shows two double-J stents (arrows) resulting from double exposure, one during inspiration and other during expiration.B, Repeat radiograph taken to reconfirm shows single double-J stent (arrows).

Double Exposure

2 exposures made on top of each other – exposure artifact

Lack of contact between film and cassette can cause “blurring” of the image

POOR SCREEN CONTACT

Poorscreen contact

Patient motion

Double exposure

Child

Double exposure

?

Hands over upper abdomen

Uncollimated Images• Causes :- The imaging plate is very

sensitive to scatter radiation,

• Primary beam collimation is reqd. to preventradiation exposure unsharp images

• Appearance :- Uncollimate, bizarre or nondiagnostic images

• Remedy :- Proper collimation should be done in accordance with the cassette size and the body part being imaged.

A, Radiograph of pelvis shows increased density over midportion and to right side of pelvis because of improper collimation.B, Subsequent pelvic radiograph with proper collimation shows uniform density over pelvis.

Delayed Scanning• Causes :- PSP changes to an intermediately

unstable state after receiving energy in the form of x-rays. This state is not stable, and if the phosphor remains unstimulated, it returns to its normal state after a prolonged delay through spontaneous phosphorescence.

• Appearance :- Delay will lead to fading of the image. 25% of stored signal will be lost in 10 min to 8 hrs after exposure and more slowly afterward.

• The fading starts from the periphery because central primary beam consists of high-energy photons, whereas the low-energy photons are in the periphery.

(Thus, distinguishes from underexposure)

• Remedy :- The delay between exposure and the readout process should be kept to minimum.

A and B, Radiographs of neck (A) and abdomen (B). Radiographs were subject to delayed readout (after 48 h). Both radiographs show decreased density in periphery as compared with center of images, as fading of image starts from periphery (arrows).

Exposure Through the Back of the Cassette

• Causes :- Poor basic knowledge of construction of cassettes

• Appearance :- Various patterns of shading according to cassette design

• Remedy :- Proper education of radiographers in handling of cassettes

Exposure through back of cassette. Radiograph of neck shows rounded radiopaquering shadow (arrow) on right lower part of neck, which if overlooked, can be wrongly diagnosed as tracheostomy tube.

Overexposure

• Causes :- Improper exposure settings. CR has a fixed dynamic range and, hence, a limited adjustment and it cannot compensate for extra noise, loss in subject contrast, and a signal out of its range of adjustment.

• Appearance :- Irreversible darkening of the image

• Remedy :- Proper exposure factors to be used based on body part and patient build.

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

Underexposure• Causes :- Improper exposure settings

• Appearance :- The image will appear grainy owing to quantum mottle. Subtle findings may be masked by the reduced signal-to-noise ratio

• Remedy :- Proper exposure factors should be used according to the body part and patient’s build, to prevent poor image quality.

A, Image shows underexposed grainy radiograph of kidney and upper bladder in which quantum mottle is evident and image quality is degraded.B, Control radiograph of same patient as in B using proper exposure factors.

Improper Grid Usage: Moiré Pattern• Causes :- Selection of grid frequency is

important, because grids with low grid line rates are known to cause a moiré pattern

• Grid with a frequency of 33 lines/cm & grid lines parallel to the plate reader’s scan lines

• Appearance :- Different types of moiré pattern• Remedy :- Grids with 60 lines/cm or more

should be used, and the grid lines should also run perpendicular to the plate reader’s laser scan lines

Improper grid usage leading to moiré 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.

grid lines and the scanning laser are parallel moiré effect

Scatter Radiation• Causes :- Imaging plate is highly sensitive to

scattered radiation. If the cassette placed in vicinity of scattered radiation.

• Appearance :- Deterioration of quality of image and imprints of objects placed over cassette

• Remedy :- No object should be kept on a cassette when it is in a radiation field.

• The cassette must be protected from all sources of ionizing radiation, including scatter radiation, as well as heat and humidity.

• If the cassette was previously exposed or kept in a field of radiation erase it before using

Scatter radiation. Cassette was kept accidentally in radiography room with pen over it for some time. Radiograph of abdomen shows fading of image with image of pen overlying lumbar spine.

Care and Carelessness• Causes :- Mishandling of imaging plate

during cleaning process

• Appearance :- Buckling will cause kink marks

• Remedy :- Cassettes and image plates should be handled with care

Scratch marks from improper handling.

Kink artifact due to buckling of imaging plate. Excretory urography radiograph shows curvilinear marks (arrows) adjacent to right upper and lower pole calyces, which can mimic pyelosinus contrast extravasations. Other kink marks are seen in course of left ureter, which can be mistaken for calculi.

Light bulb effect• Causes :- 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 relative to remainder of image. In a chest radiograph can be misread as a pnthrx or pnpertnm in a supine patient.

• Also alter the contrast and brightness of the affected portions of the image

• Remedy :- Reduce back scatter by lowering the peak kilovoltage or by more precise collimation.

Light bulb effect.A and B, Radiographs of chest (A) and abdomen (B) show darkening (arrows) in lower and outer portions of radiograph, obscuring details of image. Darkening occurs because of either high peak kilovoltage technique used in obese patients or improper collimation.

Image-Processing Artifacts

Hardware induced Software induced

Imaging plate artifacts• Causes :- Artifacts due to cracks on imaging

plate and roller induced artifacts.• As the imaging plate passes through the plate

reader, the imaging plate bends over the rollers, producing mechanical stress over a period of time and cracks. First peripherally & then centrally.

• Damage can occur due to frequent transportation.

• Artifacts can occur due to dust particles wedged over imaging plate.

• Appearance :- Cracks on the film,

Focal radio-opacities mimicking calcification of foreign bodies in soft tissues

• Remedy :- Clean the imaging plate, handle with cotton-gloves.

• Change the plate if reqd.• To remove dust regular cleaning of imaging

plates with ethyl alcohol. • Paper towels or gauze should not be used

because they leave fibers on the plate; After cleaning, leave the plate to dry for approximately 10 min [Once weekly].

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.

Artifacts due to dust particles on imaging plate.A and B, Radiographs of right elbow joint (A) and left thigh (B) show radiopacities (arrows) overlying soft tissues, which mimic soft-tissue calcification or foreign bodies but are actually due to dust over imaging plate.

• Dust in imaging plate can cause white marks on image –

• Both in film/screen and computed radiography

Roller artifactsRollers are used within the CR reader to

transport the imaging plate for scanning of latent images by the laser and subsequent erasure by the high-intensity halogen lamp. During this process, the imaging plate is constantly in contact with the rollers.

Disparity artifacts are due to malfunctioning of rollers in the digitizer, which causes defective scanning

• Appearance :- Alteration in image contrast• Remedy :- Periodic cleaning of rollers

The lower half of the image was exposed to the laser beam for a longer time, resulting in a brighter image output that rendered the image suboptimal.

Damage of imaging plate due to rollers

• Causes :- Mechanical damaging of imaging plate during transport through rollers

• Appearance:-Focal radiopacities, appearing linear or dots; {easily misdiagnosed as calcified granulomas in the lung}.

• Remedy :- Warrants immediate cleaning of rollers

Dust over rollers• Causes :- Dust deposited over imaging plate

during transport through rollers

• Appearance :- Multiple localized radiopacities

• Remedy :- Maintenance and cleaning of rubber rollers by company service personnel twice yearly

A, Radiograph of pelvis shows horizontal radiopaque lines (arrows) that can be traced outside margins of pelvis. B, 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) overlying right hypochondrium mimicking GB calculus, which is actually caused by roller damage to image plate.

Malfunctioning rollers

• Causes :- Slipping of the feed rollers, resulting in images being half read.

• Appearance :- Half-read image

• Remedy :- Periodic cleaning and recalibration of feed rollers

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 light guide.

Plate reader artifact• The light guide collects light emitted from

the beam deflector when it is scanned by the laser, which then strikes the imaging plate.

It is caused by dirt over light guide or beam deflector

• Appearance :- Linear radiopaque line

• Remedy :- Periodic cleaning of light guide by service personnel

Plate reader artifact. Lateral radiograph of knee joint shows horizontal thin radiopaque line (arrows) overlying supracondylar region. Artifact is attributed to dirt on light guide in plate reader.

Cassette-related artifact• Causes :- Cracked or weakened lead

coating on back of cassette. Scatter radiation through the back of the cassette produces black lines

• Appearance :- Linear radiolucent lines mimicking fractures (but sometimes can be traced beyond bone margins)

• Remedy :- Replacement of cassette

Cassette-related artifact. 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 caused by cracks in lead foil in back of cassette.

Software-Induced Artifacts

• Can be due to

Image transmission errors

Improper erasure settings

Image transmission errorsi. Communication error artifact

• Causes :- Power failure during image transmission (the image, after digitization, gets electronically transferred to the display station computer)

• Appearance :- Seen as missing lines or pixels in resulting image.

• Remedy :- Repeat radiograph is required.

Communication error artifact. Lower part of radiograph (arrows) of knee joint was not visualizedbecause of missing lines or pixels. Transmissionof image was truncated because of sudden power failure.

ii. Data cable malfunctioning artifact

• Causes :- Failure of data cables in the power unit of digitizer or CR reader.

• Appearance :- Alternating radiopaque and radiolucent lines

• Remedy :- Replace data cables

Data cable malfunctioning artifact.Lateral view radiograph of lumbar spine showsalternating radiopaque and radiolucent lines obscuringimage details. Problem was narrowed down tomalfunctioning data cables in computed radiographyreader.

Artifact due to improper erasure setting

• Causes :- The erasure settings for different body parts are differently calibrated, the erasure cycle time is specific for body parts.

Malfunctioning halogen bulbs (weakened power)

• Appearance :- Residual image is left in imaging plate

• Remedy :- Proper selection of body part for appropriate radiograph

Halogen vapor bulbs must be changed

Artifact due to improper erasure setting.Radiograph of kidney and upper bladder shows superimposed residual chest radiograph image,which is seen in form of ribs and clavicle shadows (black arrows). Artifact was due to inadequateerasure setting for chest radiograph. Also note two side markers (white arrows).

CONCLUSION• It is necessary to identify and pinpoint the

source and type of CR artifacts because they can cause diagnostic errors & Medicolegal implications.

• Most artifacts are due to operator error. Hence, a practical guideline to monitor the quality control program should be ensured.

• This goal can be accomplished by inspection of CR cassettes and imaging plates, quality control of equipment, and continual training of radiographers and radiologists to use this technology effectively.

THANK YOU !!!!!