Metal artifacts reduction using monochromatic images from spectral CT: Evaluation of pedicle screws in patients with scoliosis

doi:10.1016/j.ejrad.2013.02.024

European Journal of Radiology

Volume 82, Issue 8, August 2013, Pages e360-e366

https://doi.org/10.1016/j.ejrad.2013.02.024 Get rights and content

Abstract

Purpose

To evaluate the effectiveness of spectral CT in reducing metal artifacts caused by pedicle screws in patients with scoliosis.

Materials and methods

Institutional review committee approval and written informed consents from patients were obtained. 18 scoliotic patients with a total of 228 pedicle screws who underwent spectral CT imaging were included in this study. Monochromatic image sets with and without the additional metal artifacts reduction software (MARS) correction were generated with photon energy at 65 keV and from 70 to 140 keV with 10 keV interval using the 80 kVp and 140 kVp projection sets. Polychromatic images corresponded to the conventional 140 kVp imaging were also generated from the same scan data as a control group. Both objective evaluation (screw width and quantitative artifacts index measurements) and subjective evaluation (depiction of pedicle screws, surrounding structures and their relationship) were performed.

Results

Image quality of monochromatic images in the range from 110 to 140 keV (0.97 ± 0.28) was rated superior to the conventional polychromatic images (2.53 ± 0.54) and also better than monochromatic images with lower energy. Images of energy above 100 keV also give accurate measurement of the width of screws and relatively low artifacts index. The form of screws was slightly distorted in MARS reconstruction.

Conclusions

Compared to conventional polychromatic images, monochromatic images acquired from dual-energy CT provided superior image quality with much reduced metal artifacts of pedicle screws in patients with scoliosis. Optimal energy range was found between 110 and 140 keV.

Introduction

Pedicle screw placement may be associated with significant intraoperative and postoperative complications. This information is of value to surgeons using pedicle implant systems as well as to their patients [1], [2], [3], [4]. The localization accuracy is critical to minimize the perforation risk to the vertebra which is often related to a morphologic peculiarity of scoliotic vertebra, vertebral rotations, and inaccuracy of fluoroscopic images [5], [6]. The screw malposition increases the risk of injury to neural, vascular, and visceral structures due to the sophisticated structure [7], [8], [9]. This requires that the assessment of pedicle implants in spine should be more precise than in other parts.

Although there is a need of accurate assessment of pedicle implants, the diagnosis on CT images suffers metal artifacts caused by the pedicle screws. Various techniques have been developed to reduce metal artifacts in CT images [10], [11], [12], [13]. One of the main fundamental reasons of metal artifacts is the beam hardening effect, which is a common limitation in conventional polychromatic CT images [14], [15]. Recent development in dual-energy CT provided the ability to generate monochromatic images, which inherently removes the beam hardening artifacts [10], [12], [13], [16], [17].

The purpose of this study was to evaluate the effectiveness of reducing metal artifacts of pedicle screws using dual energy CT for scoliosis patients based on the width and artifacts index (AI) measurements.

Section snippets

Materials and methods

The study was conducted with the approval of our institutional review board and was compliant with Health Insurance Portability and Accountability Act regulations. Written informed consent was obtained prior to the examination.

Results

Fig. 2 shows monochromatic images of a pedicle screw from 65 to 140 keV. As energy increased, the discernibility of screw improved and the artifacts around the screw reduced. The scores for diagnostic interpretability ranged from 3.28 ± 0.45 to 0.97 ± 0.28, and the ratings of artifacts ranged from 3.14 ± 0.35 to 0.95 ± 0.25 (Table 1). The diagnostic interpretability between cortical bone and pedicle screw was graded significantly higher for images of the range from 110 to 140 keV than for those with QC

Discussion

In this study, we showed that metal artifacts caused by implanted screws in patients undergone spinal CT can be substantially reduced in monochromatic images acquired with dual energy CT. Monochromatic images within a range of energies may serve as a robust choice to evaluate the information of screw implants instead of just one single energy level. Many articles [12], [16] claim that the results of the spectral CT with the use of MARS could reduce metal artifacts, but we found by accident that

Conflict of interest

None.

Acknowledgments

The authors thank Dr. Jianying Li for their technical support in understanding the dual-energy spectral CT imaging mode and in editing the manuscript. The authors also thank Dr. Xin Zhen, Dr. Biyun Xu, Dr. Yun Shen, and Na Gao for technical assistance, and Dr. Shiying Wang for spiritual power and encouragement.

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Metal artifacts reduction using monochromatic images from spectral CT: Evaluation of pedicle screws in patients with scoliosis

Abstract

Purpose

Materials and methods

Results

Conclusions

Introduction

Section snippets

Materials and methods

Results

Discussion

Conflict of interest

Acknowledgments

Computerized Medical Imaging and Graphics

Complications of pedicle screw fixation in reconstructive surgery of the cervical spine

Spine (Phila Pa 1976)

Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members

Spine (Phila Pa 1976)

Early complications of spinal pedicle screw

European Spine Journal

Complications of the variable screw plate pedicle screw fixation

Spine (Phila Pa 1976)

Pedicle screw instrumentation in adolescent idiopathic scoliosis (AIS)

European Spine Journal

Accuracy of multilevel registration in image-guided pedicle screw insertion for adolescent idiopathic scoliosis

Spine (Phila Pa 1976)

Accuracy of pedicle screw placement in the lumbosacral spine using conventional technique: computed tomography postoperative assessment in 102 consecutive patients

Journal of Neurosurgery: Spine

Accuracy analysis of pedicle screw placement in posterior scoliosis surgery: comparison between conventional fluoroscopic and computer-assisted technique

Spine (Phila Pa 1976)

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European Spine Journal

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European Radiology

Evaluation of two iterative techniques for reducing metal artifacts in computed tomography

Radiology