Metal artifacts reduction using monochromatic images from spectral CT: Evaluation of pedicle screws in patients with scoliosis
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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These authors gave the same contribution to the paper and were recommended as co-first authors.
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These authors gave the same contribution to the paper and were recommended as corresponding authors.
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