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Stanford University Medical Center Stanford, CA
94305-5479
University of California San Francisco, CA
94143-0628
A middle-aged woman presented in the emergency department after being involved in a motor vehicle accident in which she was an unrestrained passenger. On presentation, she complained of mild neck pain. An occipital hematoma was present on physical examination. A cervical spine (C-spine) series was obtained using a computed radiography system (ADC70: Bayer, Tarrytown, NY). The initial lateral C-spine radiograph showed an apparent spondylolisthesis of at least grade 3 C5-C6. Disruption of the anterior cortex of the C5 vertebral body was also apparent (Fig. 4A).
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Because of the discrepancy between the findings seen on radiographs and those observed at clinical examination, a second lateral view was obtained. Revisualization of the area of concern showed normal alignment without loss of cortical integrity (Fig. 4B). Discordance between these studies prompted us to perform a CT examination of the C-spine. CT through the entire C-spine revealed normal findings, thus assuring us that the apparent abnormal finding of radiography was the result of an artifact.
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Other researchers have explored computed radiography artifacts but none, to our knowledge, have reported a case in which an artifact mimicked a C-spine fracture and precipitated further imaging [1]. In our case, notice that four earrings are visible in the lateral radiograph with apparently abnormal finding (Fig. 4A). Only one earring per ear is seen in subsequent radiographs (Fig. 4B). This reveals the artifact was an inadvertent double exposure, with patient motion between exposures explaining duplicate earrings and the apparent abnormal alignment.
Computed radiography using a photostimulable phosphor plate was developed in 1980 and commercialized in 1983. Its clinical use has increased worldwide. Computed radiography has been used at our institution since September 1994. Currently, all portable and emergency department X-ray examinations are performed by computed radiography. Examinations of the C-spine are typically obtained using the following parameters: 80 kV and 35-40 mAs; lateral views are obtained at 72 inches (183 cm).
To explain this artifact we must understand computed radiography physics. The linear characteristic curve of computed radiography systems allows capture of a wider range of exposure information in a single image than is possible with a screen-film system. Digital image processing performed in computed radiography systems optimizes image intensity for the dynamic range of the display device and can create a diagnostic-quality image from under-or, in this case, overexposed plates. Thus, detecting double exposures with computed radiographs versus radiographs is more difficult. It is unlikely that any interpretation in a double exposure of a radiograph would be possible because of the narrow latitude inherent in the sigmoidal characteristic curve of screen-film. Radiologists need to consider the possibility of an artifactual image with computed radiography and verify this suspicion by repeated imaging.
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