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A Virtual Endoscopy Artifact

University of Turin 10126 Turin, Italy

Virtual endoscopy is a widely accepted non-invasive method of studying air-filled structures. Its accuracy in depicting abnormalities has been assessed [1], and several artifacts commonly seen on virtual endoscopy have already been reported [2, 3]. We describe another type of artifact that, to our knowledge, has not been previously reported.

A 31-year-old woman with increasing dyspnea underwent multidetector helical CT (Light-Speed QX/i; General Electric Medical Systems, Milwaukee, WI) examination of the neck and upper thorax. Scanning was performed as a one breath-hold acquisition with the patient in the supine position. IV contrast material (Iomeron 250; Bracco, Milano, Italy) was given because malignancy was suspected. The CT data were downloaded to a workstation (Sun Medical; Shiga, Japan); virtual endoscopic images were obtained using dedicated software (Smooth Navigator, Advantage Windows 3.1; General Electric Medical Systems). On virtual endoscopy, an approximately 2-mm-thick septum through the tracheal wall under the glottic plane was observed (Fig. 2A). On the default corresponding axial reference scan, no intraluminal defect was visible. After setting the appropriate window width and window level parameters, we detected some streaks (Fig. 2B) that we determined to be beam-hardening artifacts caused by the presence of the contrast material bolus in left brachiocephalic vein overlying the tracheal lumen. The densest streak was depicted as the endoluminal septum on virtual endoscopy software.

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —31-year-old woman who presented with increasing dyspnea. Virtual bronchial endoscopic image shows approximately 2-mm-thick septum through tracheal wall under glottic plane. Inset shows projection of pyramid view cone of axial image. Base of pyramid = field of view, tip of pyramid = viewing location, IPR = inferior posterior right, A = anterior, P = posterior, L = left, R = right.

View larger version (122K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —31-year-old woman who presented with increasing dyspnea. After adjustments for appropriate window width and window level parameters, two hyperdense streaks—one less opaque (arrowhead)—are visible on corresponding axial reference CT scan. Streaks are beam-hardening artifacts caused by contrast material bolus in left brachiocephalic vein overlying tracheal lumen. Densest streak (arrows) was visualized as the endoluminal septum on virtual endoscopy software.

In our experience, avoiding incorrect diagnosis of intraluminal lesions requires comparing the virtual endoscopic images with axial CT scans. Using different parameters for window width and window level can be helpful in identifying high-density materials (such as intraluminal contrast material or metallic clips) close to hollow structures that may cause beam-hardening artifacts.

The literature describes different types of artifacts affecting virtual endoscopy [2, 3], with causes ranging from uncooperative patient behaviors (breathing, swallowing, or moving) to the scanning process itself or specific visualization methods (stairstep and smoothing artifacts, longitudinal blurring, and longitudinal distortion). In this patient, we found that a potentially misleading artifact may arise from the presence of high-density materials close to the navigation site. Radiologists should be aware of this potential pitfall during virtual endoscopy so that they can take the most appropriate technical measures and thus avoid incorrectly diagnosing endoluminal lesions.

References

1. Rogalla P, Terwisscha van Scheltinga J, Hamm B. Virtual endoscopy and related 3D techniques. Heidelberg, Germany: Springer-Verlag, 2001
2. Bode A, Dammann F, Pelikan EH, et al. Analysis of artifacts by virtual endoscopy visualization of spiral CT data [in German]. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 2001;173:245 -252[Medline]
3. Springer P, Stohr B, Giacomuzzi SM, et al. Virtual computed tomography colonoscopy: artifacts, image quality, and radiation dose in a cadaver study. Eur Radiol 2000;10:183 -187[Medline]

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This Article Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cesarani, F. Articles by Gandini, G. Search for Related Content PubMed PubMed Citation Articles by Cesarani, F. Articles by Gandini, G. Social Bookmarking                      What's this?