Journal List > J Korean Soc Spine Surg > v.9(4) > 1036030

Yeom, Chung, Lee, Kim, Choy, Kang, Kim, Kim, and Lee: Reduction of Metal Artifact around Titanium Alloy-based Pedicle Screws on CT Scan Images: An Approach using a Digital Image Enhancement Technique

Abstract

Study Design

A study on the development of an algorithm to enhance computed tomographic images

Objectives

The purpose of this study was to develop an approach to reduce the metal artifact that appears around pedicle screws, and thus to facilitate the evaluation of pedicle screw positions on CT scan images.

Summary of Literature Review

Metal artifact caused by pedicle screws significantly reduces the interpretability of computed tomography images.

Materials and Methods

We describe the development of an algorithm that processes CT scan images on a personal computer using a digital image enhancement technique. The algorithm improves CT images by transforming image pixel values using a proper transformation curve that takes into account the characteristic distribution pattern of metal artifact caused by pedicle screws made of titanium alloys. We implemented this algorithm in a program that reconstructs the resulting images in arbitrary planes and in axial, coronal, and sagittal planes. The software was tested with spiral CT scan images of 38 patients containing 190 pedicle screws.

Results

In all test cases, our algorithm generated images with less metal artifact, better soft tissue visualization and clearer screw outlines than conventional bone setting. In addition, images reconstructed in arbitrary planes increase the convenience and confidence of localizing screw positions.

Conclusions

The algorithm effectively decreases metal artifact and improved pedicle screw localization.

REFERENCES

1). Crane R. A simplified approach to image processing: classical and modern techniques in C. New Jersey, Pren -tice Hall PTR: 110-143. 1997.
2). Kalender WA, Hebel R and Ebersberger J. Reduction of CT artifacts caused by metallic implants. Radiol. 164:576–577. 1987.
crossref
3). Pratt WK. Digital Image Processing. 2nd ed.New York: Wiley-Interscience;p. 263–322. 1991.
4). Robertson DD, Weiss PJ, Fishman EK, Magid D and Walker PS. Evaluation of CT techniques for reducing artifacts in the presence of metallic orthopedic implants. J Comput Assist Tomogr. 12:236–241. 1988.
crossref
5). Robertson DD, Yuan J, Wang G and Vannier MW. Total hip prosthesis metal artifact suppression using iterative deblurring reconstruction. J Comput Assist Tomogr. 21:293–298. 1997.
6). Wang G, Frei T and Vannier MW. Fast iterative algorithm for metal artifact reduction in X-ray CT. Acad Radiol. 7:607–614. 2000.
crossref
7). Yeom JS, Choy WS, Kim WJ, Kim HY, Kang JW, Kim YH, Kim NK and Lee JB. A patient-specific surgical simulation system for spinal screw insertion composed of virtual roentgenogram, virual C-arm, and rapid prototyping. J of Korean Orthop Assoc. 36:161–166. 2001.
8). Yoo JU, Ghanayem A, Petersilge C and Lewin J. Accuracy of using computed tomography to identify pedicle screw placement in cadaveric human lumbar spine. Spine. 22:2668–2671. 1997.
crossref
9). Zhao S, Robertson DD, Wang G, Whiting B and Bae KT. X-ray CT metal artifact reduction using wavelets: an application for imaging total hip prostheses. IEEE Trans Med Imaging. 19:1238–1247. 2000.
crossref

Fig. 1.
Postoperative CT scan images in soft tissue setting (A) and bone setting (B) show metal artifact appearing around the pedicle screws.
jkss-9-280f1.tif
Fig. 2.
Two reconstructed three-dimensional images of a screw system demonstrate difference in thickness of screws according to difference in threshold values (A.2000, B. 2500).
jkss-9-280f2.tif
Fig. 3.
Two methods for analysis of Hounsfield numbers of CT scan images are shown. A. Pixel values are presented by a line profile. B. Pixel values are tabulated.
jkss-9-280f3.tif
Fig. 4.
Pixel value remapping using the first curve is shown. The pixel values are converted to some other values according to the curve (A). On the resulting image, metal artifact is reduced, and the screw outlines are displayed (B). It also provides better visualization of soft tissue than the bone setting.
jkss-9-280f4.tif
Fig. 5.
Pixel value remapping using the second curve (A) results in an image with clear outlines of both the screws and bony structures (B), which is more useful in determining screw position than the image produced by the first curve (C).
jkss-9-280f5.tif
Fig. 6.
User interface of the final program is shown. A. Images in axial, coronal, and sagittal windows are displayed simultaneously, and ‘ line indicators’ on each window interre-late the image contents. B. Once the arbitrary plane reconstruction function is turned on, and a user places a line on any of the three multi-planar reconstruction images, then an image perpendicular to the plane and including the line is displayed on the right lower window.
jkss-9-280f6.tif
TOOLS
Similar articles