AJDRAJNR - American Journal of Neuroradiology

Published ahead of print on November 20, 2008
doi: 10.3174/ajnr.A1378
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CT Radiation Dose for Computer-Assisted Endoscopic Sinus Surgery: Dose Survey and Determination of Dose-Reduction Limits

C.B. Nauera, A. Eichenbergerb, P. Dubachb, J. Grallaa and M. Caversacciob

a Institute for Diagnostic and Interventional Neuroradiology, University Hospital and University of Berne, Berne, Switzerland
b Department of Otorhinolaryngology/Head and Neck Surgery, University Hospital and University of Berne, Berne, Switzerland


Figure 1
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  		Fig 1. A and B, A surface-rendered image reconstructed on an Advantage Windows workstation (GE Healthcare) from a CT dataset performed with a CTDIvol of 65 mGy (A) shows no discernible noise, whereas with a CTDIvol of 9.5 mGy (B), delineation of facial contours is impaired due to image noise which might, according to our initial hypothesis, render surface registration impossible.


Figure 2
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  		Fig 2. Screenshot from the navigation system display shows the information the ENT surgeon has available during the intervention. A low-dose dataset (CTDIvol of 3.1 mGy) was used.


Figure 3
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  		Fig 3. This screenshot from the planning software iPlan shows a CT dataset with coronal and sagittal reformations. The central screw head pit of the screw in the zygomatic bone is heavily magnified for positioning the marker circle used for the accuracy measurements.


Figure 4
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  		Fig 4. Results of the dose survey. Doses used for CAS-CT (gray) and diagnostic sinus CT (black) in 15 CT scanners. O is our institution before the CAS-CT protocol was adapted.


Figure 5
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  		Fig 5. Scatterplot of accuracy measurements in millimeters for screw-marked points depicted on the y-axis. CAS-CT dose used in mGy depicted on the logarithmic x-axis. Each column represents the accuracy in mm for 7 screw-marked points on 4 cadaveric heads for registration with CAS-CT at a given dose. The regression line shows no clinically significant slope for accuracy with exponential growth of the radiation dose in the dose interval tested. Note that slight irregularities of the regression line due to the limited resolution of the software used for statistical analysis were straightened by using Photoshop (Adobe Systems, San Jose, Calif), without altering the content of the graphic.


Figure 6
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  		Fig 6. Sinus CT in an edge-enhanced (bone) algorithm performed with a CTDIvol of 65 mGy (A) and with a CTDIvol of 9.5 mGy (B). The sevenfold dose difference is not appreciated well, though image B is obviously noisier than A.





Copyright © 2009 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X