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181
Pictorial
Essay
..
Artifacts Steven
in Computed
L. Solomon,1
R. Gilbert
Jost,
Radiography Harvey
S. Glazer,
Storage-phosphor digital radiographic systems are becoming widely used in a variety of diagnostic procedures. The equipment is reliable and produces images of consistently high quality. However, the images may contain artifacts directly related to the digital techniques used, to the phosphor imaging plate, or to radiography in general. This article illustrates many of the artifacts encountered that are specific to computed radiography, some of which can simulate pathologic lesions. Their causes and remedies are discussed briefly.
Computed
systems that use photostimulable been introduced into radiology departments throughout the world over the past 5 years in increasing numbers. More than 50 systems are in operation in the United States and approximately 500 systems have been installed in Japan (Armstrong D, Fuji Medical Systems U.S.A., personal communication). Many articles have described the potential benefits of computed radiography and its clinical usefulness in chest, pediatric, genitourinary, gastrointestinal, vascular, and neuroradiology imaging [1 -6]. A Philips Computed Radiography 901 system (Philips Medical Systems, Shelton, CT) has been in operation at our institute for more than 3 years and is used for nearly all the inpatient mobile (“portable”) chest and abdominal radiographs [4]. The device has been reliable and image quality has been excellent, but on occasion, puzzling artifacts have been encountered, some of which have the potential to mimic true disease. Artifacts that are not unique to computed radiography (fogging, double exposure, foreign bodies) can be modified in storage
severity
have
or appearance
Received I
radiographic
phosphors
October
by computed
1 5, 1990; accepted
All authors: Edward Mallinckrodt
reprint
requests
AJR 157:181-185,
radiographic
after revision
systems.
December
Institute of Radiology,
Stuart
S. Sagel,
“Light-Bulb”
57-0181
and Paul L. Molina
Effect
The lower, outer portions of a film occasionally appear darkened relative to the remainder of the image (Fig. 1 ). This artifactual darkening, referred to as the light-bulb effect by Fuji Medical Systems, is caused by back-scattered radiation entering the photostimulable phosphor imaging plate from the patient’s bed. This artifact is seen most frequently when the exposure is increased for obese patients or when the X-ray beam has not been collimated to the region of interest. The wide dynamic range and high sensitivity of the imaging plate makes computed radiography more susceptible to this artifact than conventional film-screen portable examinations. With chest radiography, the artifact could be misconstrued as representing a pneumothorax or pneumoperitoneum in a supine patient; in addition, it can alter the contrast and brightness of the affected portions of the image, potentially obscuring abnormalities. Reducing backscatter by lowering the kilovoltage or by more precise collimation will limit the prevalence and impact of this artifact. A lead backing applied to the cassette has been proposed as a possible solution (Armstrong D, personal communication).
Fogging The wide dynamic range and high sensitivity of the imaging plate used in computed radiography results in a greater susceptibility to fogging (Fig. 2). Because the imaging plates have such a high sensitivity, extra precautions should be taken so that they are not exposed to extraneous radiation.
1 7, 1990.
Washington
University School of Medicine, 51 0 S. Kingshighway
to S. L. Solomon. July 1991 0361 -803x/91/1
Dixie J. Anderson,
© American
Roentgen
Ray Society
Blvd. , St. Louis, MO 631 10. Address
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
182
SOLOMON
ET
AL.
AJR:157,July
1991
dynamic range of the imaging plate used in computed radiography allows an image similar in density to a single exposure to result from most inadvertent double exposures (Fig. 3). If the relative exposure of both examinations is comparable, they will be equally well seen on the output image and the nature of the problem should be readily apparent. If one exposure is significantly less than the other, the artifact may be subtle and simulate abnormalities. A related and visually indistinguishable situation can occur if a latent image on the imaging plate has not been completely erased. Computed radiographic systems are capable of erasing an imaging plate that has received up to five times the normal exposure. If an exposure greater than this has occurred, the imaging plate is transported to a special unerased plate tray after it has been read. If this imaging plate is inadvertently used for another examination, a double-exposure artifact may result. Incompletely erased imaging plates should be carefully erased in the “imaging plate erasure mode.”
Quantum Fig. 1.-Light-bulb graph patient’s
eflect.
(arrows) are darkened bed. Wide
dynamic
Lower, outer portions
of this computed
radio-
because of back-scattered radiation from range and high sensitivity of photostimulable
phosphor Imaging plate make computed radiographs much more susceptible to this artifact than conventional portable film-screen radiographs.
Double
Exposure
With conventional film-screen posures result in a darkened,
Fig. 2.-Fogging
techniques, unreadable
most double eximage. The wide
on a computed radiograph. by exposure to extraneous radiation exposure.
The wide dynamic range of the imaging plate can create an image when underexposure or overexposure would result in an unreadable image with conventional film-screen methods. In the case of marked underexposure, the image will appear grainy owing to quantum mottle (Fig. 4). Such images, which can be readily identified by noting a high sensitivity number in the parameter display area, must be interpreted with caution, as subtle findings may not be apparent because of the reduced signal-to-noise ratio.
artifacts
A, Lower half of image is darkened
prevent inadvertent
Mottle
B, Fogging in lower portion of image is caused degree with conventional film-screen techniques.
by radium
radiation. High sensitivity of imaging plates requires
implants
placed
in pelvis
to treat
cervical
cancer.
We have
that extra
precautions
not seen
this artifact
be taken
to
to the same
ARTIFACTS
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
AJR:157, July 1991
IN COMPUTED
RADIOGRAPHY
183
.
Fig. 3.-Double exposures on computed radiograph. Horizontally oriented abdominal examination is seen overlying dominant chest study. Portions of right ribs (arrow) and right iliac crest(arrowhead) are apparent.
Fig. 4.-Quantum mottle on computed radiograph. Marked underexposure of this abdominal examination results in an interpretable, albeit grainy and suboptimal, image because of wide dynamic range of imaging plate.
Simulated
tamed in the image. If the expected density range is exceeded, information can be lost (Fig. 6). For example, the chest algorithm does not guarantee the preservation of image information from the skin. Fortunately, most losses of information will occur outside of the regions of interest for the examination. If an algorithm for the wrong body part is chosen, the density and contrast settings will not be optimal for the body part imaged (Fig. 7). The “auto” modes use the entire image for histogram analysis as opposed to the “semiauto” modes, which only perform histogram analysis on selected portions of the image data. The shape of collimation is critically important in the auto modes on computed radiographic devices that use firstgeneration software. If a collimation border is more than 3#{176} from parallel to the edge of the imaging plate, the area of collimation will not be recognized as such and will be included in the subsequent determination of image density and contrast. This can result in marked image darkening in the region of interest (Fig. 8).
Diaphragmatic
Calcification
The unsharp masking edge-enhancement algorithm used in the edge-enhanced computed radiographic image can resuIt in artifactual black and white bands at the interface of structures with markedly disparate densities. This can result in the appearance of diaphragmatic calcification (Fig. 5). The erroneous diagnosis of asbestos exposure could result. This artifact is always much less apparent on the non-edgeenhanced image, an important differential point. Comparison with prior radiographs, if available, or a follow-up conventional radiograph is helpful in ambiguous cases. If this artifact is problematic, the spatial frequency processing parameters can be modified to lessen the effect.
Alterations
in Image
Contrast
and Density
A contrast resolution of 1 0 bits per pixel (1 024 shades of gray) was chosen in the design of the currently used cornputed radiographic systems. The imaging plate, on the other hand, has a dynamic range exceeding 1 0. The image inforrnation contained on the imaging plate must be mapped onto these relatively few shades of gray. As part of this mapping process, the imaging plate is scanned twice. The first scan is obtained with a high-speed low-intensity laser, and histogram analysis is performed on the light emission from portions of the image. The portions of the image examined are determined by the algorithm chosen for the image. The result of this analysis determines the density and contrast parameters used in the final reading of the imaging plate and creation of the output image. The algorithms designed for each body part make certain assumptions about the expected useful density range con-
Foreign
Bodies
As with conventional film-screen systems, foreign bodies, such as dust, can adhere to the imaging plate and result in artifacts simulating calcifications. Spillage of a liquid on the imaging plate prior to its processing by the computed radiographic device is shown in Figure 9. The repetitive nature of the artifact is due to the rollers used in the plate transport mechanism. Newer computed radiographic systems use belts to transport the plates and therefore would not propagate the artifact.
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184
SOLOMON
Fig. 5.-5imulated
diaphragmatic
calcification
on computed
ET AL.
AJR:157,
radiograph.
A and B, Edge-enhanced image (A) shows apparent calcification (arrows) of right hemidiaphragm that is not seen on unenhanced image (B), an important differential point. This artifact almost always
involves right hemidiaphragm, probably because of heart and pericardial fat overlying left hemidiaphragm, which reduce abrupt changes in tissue density at this site. A similar artifact is also seen frequently
at edges
of both breasts.
Fig. 7.-Altered contrast parameters on computed radiograph. This chest image was inadvertently printed with an algorithm designed for mandible.
Result
is a darkened
image
with suboptimal
contrast.
Malfunction
The normal computed radiographic output consists of two one processed to resemble a normal film-screen radiograph and one processed with a degree of edge enhancement and widened latitude. On occasion, images have been observed in which the edge enhancement has been augmented dramatically (Fig. 1 0). This is probably the result of an alteration of the image processing parameters stored in images,
Fig. 6.-Loss of information on computed radiograph. External portions of nasogastric, feeding, and endotracheal tubes are not visualized (arrows) because expected useful density range for a skull examination has been exceeded at these sites.
Fig. 8.-Poor collimation on computed computed radiographic software relies heads) being less than 3#{176} from parallel
radiograph.
First generation
on collimation
margins
of
(arrow-
to edge of imaging plate when “auto” modes are used. If this angle is exceeded, as has occurred in this Image,
Equipment
July 1991
area
of collimation
will not be recognized
as such,
and
display
algorithm will include this area in its determination of image density and contrast. Result will be overall darkening of region of interest.
memory due to noise from the electrical power supply (Hishinuma K, Fuji Medical Systems Japan, Inc., personal communication). This artifact has been seen only on edge-enhanced images, a potential clue to its presence in more subtle cases. The problem should be corrected by turning off and restarting the computed radiographic device. The power sup-
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
AJR:157,
July 1991
ARTIFACTS
IN COMPUTED
RADIOGRAPHY
Fig. 1 1 -zipper
185
artifact.
Fig. 9.-Foreign substances on a computed radiograph. A liquid, possibly blood, was spilled on imaging plate during this intraoperative examination. Owing to rollers used in early computed radiographic equipment, this manifests as an artifact (arrows) seen all across image at constant
puted radiograph portion of vertebral of a white vertical
intervals.
caused by temporary
Information
from central
portion
of this corn-
(arrowheads) is missing, with apparent absence of a bodies. Amount of information lost is reflected by width band at right side of image (arrows). This artifact is
interruption of image-plate
tinues to be transported through reading sudden drop in power supply voltage.
device.
reading while plate concause
is probably
a
ply noise and variance may need to be checked if the problem is recurrent. Rarely, images are seen in which multiple vertical scan lines are missing with apparent narrowing of the affected portion of the image (Fig. 1 1), referred to by us as the “zipper” artifact. The exact amount of missing information is reflected by the width of a lucent vertical band at the right side of the image. This artifact results when the reading process is temporarily discontinued while the imaging plate continues to move through the reading device. The cause is probably a sudden drop in the power supply voltage (Hishinuma K, personal communication).
REFERENCES 1 . Fajardo LL, Hillman BJ, Hunter TB, Claypool HR. Westerman B. Excretory urography using computed radiography. 1987:162:345-351
Fig. 10.-Abnormal edge enhancement. Edge-enhancement image processing parameters have been altered on this computed radiograph, resulting in dramatic augmentation of edge enhancement. This artifact probably is due to noise from electrical power supply and should be corrected by turning off and restarting computed radiographic device.
BR, Mockbee Radiology
2. Kangarloo H, Boechat Ml, Barbaric Z, et al. Two-year clinical experience with a computed radiography system. AJR 1988:151:605-608 3. Kogutt MS. Jones JP, Perkins DD. Low-dose digital computed radiography in pediatric chest imaging. AJR 1988:151 :775-779 4. Sagel 55, Jost AG, Glazer HS, et al. Digital mobile radiography. J Thorac Imaging 1990;5(1):36-48 5. Tateno V. linuma T. Takano M, eds. Computed radiography. Tokyo: Springer-Verlag, 1987 6. Yang PJ, Seeley GW, Carmody RF, Seeger JF, Yoshino MT. Mockbee B. Conventional vs computed radiography: evaluation of myelography. AJNR 1988;9: 165-168
181
Pictorial
Essay
..
Artifacts Steven
in Computed
L. Solomon,1
R. Gilbert
Jost,
Radiography Harvey
S. Glazer,
Storage-phosphor digital radiographic systems are becoming widely used in a variety of diagnostic procedures. The equipment is reliable and produces images of consistently high quality. However, the images may contain artifacts directly related to the digital techniques used, to the phosphor imaging plate, or to radiography in general. This article illustrates many of the artifacts encountered that are specific to computed radiography, some of which can simulate pathologic lesions. Their causes and remedies are discussed briefly.
Computed
systems that use photostimulable been introduced into radiology departments throughout the world over the past 5 years in increasing numbers. More than 50 systems are in operation in the United States and approximately 500 systems have been installed in Japan (Armstrong D, Fuji Medical Systems U.S.A., personal communication). Many articles have described the potential benefits of computed radiography and its clinical usefulness in chest, pediatric, genitourinary, gastrointestinal, vascular, and neuroradiology imaging [1 -6]. A Philips Computed Radiography 901 system (Philips Medical Systems, Shelton, CT) has been in operation at our institute for more than 3 years and is used for nearly all the inpatient mobile (“portable”) chest and abdominal radiographs [4]. The device has been reliable and image quality has been excellent, but on occasion, puzzling artifacts have been encountered, some of which have the potential to mimic true disease. Artifacts that are not unique to computed radiography (fogging, double exposure, foreign bodies) can be modified in storage
severity
have
or appearance
Received I
radiographic
phosphors
October
by computed
1 5, 1990; accepted
All authors: Edward Mallinckrodt
reprint
requests
AJR 157:181-185,
radiographic
after revision
systems.
December
Institute of Radiology,
Stuart
S. Sagel,
“Light-Bulb”
57-0181
and Paul L. Molina
Effect
The lower, outer portions of a film occasionally appear darkened relative to the remainder of the image (Fig. 1 ). This artifactual darkening, referred to as the light-bulb effect by Fuji Medical Systems, is caused by back-scattered radiation entering the photostimulable phosphor imaging plate from the patient’s bed. This artifact is seen most frequently when the exposure is increased for obese patients or when the X-ray beam has not been collimated to the region of interest. The wide dynamic range and high sensitivity of the imaging plate makes computed radiography more susceptible to this artifact than conventional film-screen portable examinations. With chest radiography, the artifact could be misconstrued as representing a pneumothorax or pneumoperitoneum in a supine patient; in addition, it can alter the contrast and brightness of the affected portions of the image, potentially obscuring abnormalities. Reducing backscatter by lowering the kilovoltage or by more precise collimation will limit the prevalence and impact of this artifact. A lead backing applied to the cassette has been proposed as a possible solution (Armstrong D, personal communication).
Fogging The wide dynamic range and high sensitivity of the imaging plate used in computed radiography results in a greater susceptibility to fogging (Fig. 2). Because the imaging plates have such a high sensitivity, extra precautions should be taken so that they are not exposed to extraneous radiation.
1 7, 1990.
Washington
University School of Medicine, 51 0 S. Kingshighway
to S. L. Solomon. July 1991 0361 -803x/91/1
Dixie J. Anderson,
© American
Roentgen
Ray Society
Blvd. , St. Louis, MO 631 10. Address
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
182
SOLOMON
ET
AL.
AJR:157,July
1991
dynamic range of the imaging plate used in computed radiography allows an image similar in density to a single exposure to result from most inadvertent double exposures (Fig. 3). If the relative exposure of both examinations is comparable, they will be equally well seen on the output image and the nature of the problem should be readily apparent. If one exposure is significantly less than the other, the artifact may be subtle and simulate abnormalities. A related and visually indistinguishable situation can occur if a latent image on the imaging plate has not been completely erased. Computed radiographic systems are capable of erasing an imaging plate that has received up to five times the normal exposure. If an exposure greater than this has occurred, the imaging plate is transported to a special unerased plate tray after it has been read. If this imaging plate is inadvertently used for another examination, a double-exposure artifact may result. Incompletely erased imaging plates should be carefully erased in the “imaging plate erasure mode.”
Quantum Fig. 1.-Light-bulb graph patient’s
eflect.
(arrows) are darkened bed. Wide
dynamic
Lower, outer portions
of this computed
radio-
because of back-scattered radiation from range and high sensitivity of photostimulable
phosphor Imaging plate make computed radiographs much more susceptible to this artifact than conventional portable film-screen radiographs.
Double
Exposure
With conventional film-screen posures result in a darkened,
Fig. 2.-Fogging
techniques, unreadable
most double eximage. The wide
on a computed radiograph. by exposure to extraneous radiation exposure.
The wide dynamic range of the imaging plate can create an image when underexposure or overexposure would result in an unreadable image with conventional film-screen methods. In the case of marked underexposure, the image will appear grainy owing to quantum mottle (Fig. 4). Such images, which can be readily identified by noting a high sensitivity number in the parameter display area, must be interpreted with caution, as subtle findings may not be apparent because of the reduced signal-to-noise ratio.
artifacts
A, Lower half of image is darkened
prevent inadvertent
Mottle
B, Fogging in lower portion of image is caused degree with conventional film-screen techniques.
by radium
radiation. High sensitivity of imaging plates requires
implants
placed
in pelvis
to treat
cervical
cancer.
We have
that extra
precautions
not seen
this artifact
be taken
to
to the same
ARTIFACTS
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
AJR:157, July 1991
IN COMPUTED
RADIOGRAPHY
183
.
Fig. 3.-Double exposures on computed radiograph. Horizontally oriented abdominal examination is seen overlying dominant chest study. Portions of right ribs (arrow) and right iliac crest(arrowhead) are apparent.
Fig. 4.-Quantum mottle on computed radiograph. Marked underexposure of this abdominal examination results in an interpretable, albeit grainy and suboptimal, image because of wide dynamic range of imaging plate.
Simulated
tamed in the image. If the expected density range is exceeded, information can be lost (Fig. 6). For example, the chest algorithm does not guarantee the preservation of image information from the skin. Fortunately, most losses of information will occur outside of the regions of interest for the examination. If an algorithm for the wrong body part is chosen, the density and contrast settings will not be optimal for the body part imaged (Fig. 7). The “auto” modes use the entire image for histogram analysis as opposed to the “semiauto” modes, which only perform histogram analysis on selected portions of the image data. The shape of collimation is critically important in the auto modes on computed radiographic devices that use firstgeneration software. If a collimation border is more than 3#{176} from parallel to the edge of the imaging plate, the area of collimation will not be recognized as such and will be included in the subsequent determination of image density and contrast. This can result in marked image darkening in the region of interest (Fig. 8).
Diaphragmatic
Calcification
The unsharp masking edge-enhancement algorithm used in the edge-enhanced computed radiographic image can resuIt in artifactual black and white bands at the interface of structures with markedly disparate densities. This can result in the appearance of diaphragmatic calcification (Fig. 5). The erroneous diagnosis of asbestos exposure could result. This artifact is always much less apparent on the non-edgeenhanced image, an important differential point. Comparison with prior radiographs, if available, or a follow-up conventional radiograph is helpful in ambiguous cases. If this artifact is problematic, the spatial frequency processing parameters can be modified to lessen the effect.
Alterations
in Image
Contrast
and Density
A contrast resolution of 1 0 bits per pixel (1 024 shades of gray) was chosen in the design of the currently used cornputed radiographic systems. The imaging plate, on the other hand, has a dynamic range exceeding 1 0. The image inforrnation contained on the imaging plate must be mapped onto these relatively few shades of gray. As part of this mapping process, the imaging plate is scanned twice. The first scan is obtained with a high-speed low-intensity laser, and histogram analysis is performed on the light emission from portions of the image. The portions of the image examined are determined by the algorithm chosen for the image. The result of this analysis determines the density and contrast parameters used in the final reading of the imaging plate and creation of the output image. The algorithms designed for each body part make certain assumptions about the expected useful density range con-
Foreign
Bodies
As with conventional film-screen systems, foreign bodies, such as dust, can adhere to the imaging plate and result in artifacts simulating calcifications. Spillage of a liquid on the imaging plate prior to its processing by the computed radiographic device is shown in Figure 9. The repetitive nature of the artifact is due to the rollers used in the plate transport mechanism. Newer computed radiographic systems use belts to transport the plates and therefore would not propagate the artifact.
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
184
SOLOMON
Fig. 5.-5imulated
diaphragmatic
calcification
on computed
ET AL.
AJR:157,
radiograph.
A and B, Edge-enhanced image (A) shows apparent calcification (arrows) of right hemidiaphragm that is not seen on unenhanced image (B), an important differential point. This artifact almost always
involves right hemidiaphragm, probably because of heart and pericardial fat overlying left hemidiaphragm, which reduce abrupt changes in tissue density at this site. A similar artifact is also seen frequently
at edges
of both breasts.
Fig. 7.-Altered contrast parameters on computed radiograph. This chest image was inadvertently printed with an algorithm designed for mandible.
Result
is a darkened
image
with suboptimal
contrast.
Malfunction
The normal computed radiographic output consists of two one processed to resemble a normal film-screen radiograph and one processed with a degree of edge enhancement and widened latitude. On occasion, images have been observed in which the edge enhancement has been augmented dramatically (Fig. 1 0). This is probably the result of an alteration of the image processing parameters stored in images,
Fig. 6.-Loss of information on computed radiograph. External portions of nasogastric, feeding, and endotracheal tubes are not visualized (arrows) because expected useful density range for a skull examination has been exceeded at these sites.
Fig. 8.-Poor collimation on computed computed radiographic software relies heads) being less than 3#{176} from parallel
radiograph.
First generation
on collimation
margins
of
(arrow-
to edge of imaging plate when “auto” modes are used. If this angle is exceeded, as has occurred in this Image,
Equipment
July 1991
area
of collimation
will not be recognized
as such,
and
display
algorithm will include this area in its determination of image density and contrast. Result will be overall darkening of region of interest.
memory due to noise from the electrical power supply (Hishinuma K, Fuji Medical Systems Japan, Inc., personal communication). This artifact has been seen only on edge-enhanced images, a potential clue to its presence in more subtle cases. The problem should be corrected by turning off and restarting the computed radiographic device. The power sup-
Downloaded from www.ajronline.org by 192.171.202.224 on 10/24/15 from IP address 192.171.202.224. Copyright ARRS. For personal use only; all rights reserved
AJR:157,
July 1991
ARTIFACTS
IN COMPUTED
RADIOGRAPHY
Fig. 1 1 -zipper
185
artifact.
Fig. 9.-Foreign substances on a computed radiograph. A liquid, possibly blood, was spilled on imaging plate during this intraoperative examination. Owing to rollers used in early computed radiographic equipment, this manifests as an artifact (arrows) seen all across image at constant
puted radiograph portion of vertebral of a white vertical
intervals.
caused by temporary
Information
from central
portion
of this corn-
(arrowheads) is missing, with apparent absence of a bodies. Amount of information lost is reflected by width band at right side of image (arrows). This artifact is
interruption of image-plate
tinues to be transported through reading sudden drop in power supply voltage.
device.
reading while plate concause
is probably
a
ply noise and variance may need to be checked if the problem is recurrent. Rarely, images are seen in which multiple vertical scan lines are missing with apparent narrowing of the affected portion of the image (Fig. 1 1), referred to by us as the “zipper” artifact. The exact amount of missing information is reflected by the width of a lucent vertical band at the right side of the image. This artifact results when the reading process is temporarily discontinued while the imaging plate continues to move through the reading device. The cause is probably a sudden drop in the power supply voltage (Hishinuma K, personal communication).
REFERENCES 1 . Fajardo LL, Hillman BJ, Hunter TB, Claypool HR. Westerman B. Excretory urography using computed radiography. 1987:162:345-351
Fig. 10.-Abnormal edge enhancement. Edge-enhancement image processing parameters have been altered on this computed radiograph, resulting in dramatic augmentation of edge enhancement. This artifact probably is due to noise from electrical power supply and should be corrected by turning off and restarting computed radiographic device.
BR, Mockbee Radiology
2. Kangarloo H, Boechat Ml, Barbaric Z, et al. Two-year clinical experience with a computed radiography system. AJR 1988:151:605-608 3. Kogutt MS. Jones JP, Perkins DD. Low-dose digital computed radiography in pediatric chest imaging. AJR 1988:151 :775-779 4. Sagel 55, Jost AG, Glazer HS, et al. Digital mobile radiography. J Thorac Imaging 1990;5(1):36-48 5. Tateno V. linuma T. Takano M, eds. Computed radiography. Tokyo: Springer-Verlag, 1987 6. Yang PJ, Seeley GW, Carmody RF, Seeger JF, Yoshino MT. Mockbee B. Conventional vs computed radiography: evaluation of myelography. AJNR 1988;9: 165-168
