口腔DDR系统的应用失真率及固定修复金属材料对MRI成像影响的研究
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摘要
在根管内植入预成金属桩,然后使用复合树脂形成桩核,再进行全冠修复,是进行残根残冠保存修复的重要手段。它减少了患者的诊疗次数、节省了诊疗时间、降低了根折的风险。
预成金属桩根内桩长与根长的比例在适当的范围内(即2/3~3/4),对确保桩-核冠的固位和牙根的抗折力有重要的意义。初次植入预成桩后用口腔直接数字成像系统(Direct Digital Radiography,DDR)拍摄X线数字牙片(Digital Radiography),观测根内桩长与根长的比例,并对桩植入的深度加以校正,以达到最佳的植入深度、位置,从而可以获得理想的修复效果。
由于直接数字成像系统受到多种因素的影响,在临床中影像常被放大或缩小,影响对金属桩植入的判断。如何准确判断成像误差,成为需要关注的问题。本研究通过用测量软件在X线数字牙片上测量预成金属桩的长度,与实际长度比较,计算并考查口腔直接数字成像系统在预成金属桩植入应用中的失真率,以便为临床医生准确判读X线数字牙片及放射科改进拍摄技术提供参考。
研究结果表明:在临床预成金属桩植入中,通过现有常用方法获得的口腔直接数字成像根尖片具有很大的失真率,尚不能为预成金属桩的植入提供精确的指引,需要通过采取规范放射技师的拍摄技术等相应措施减小失真率以适合临床应用的需要,以期充分发挥口腔直接数字成像系统的优势。
MRI(Magnetic Resonance Imaging)是目前头颈部疾病最常用的影像学诊断设备之一,由于其多功能、多序列、多参数、多平面成像以及较高的软组织分辨力而被广泛应用于临床疾病的诊断与治疗。但由于其成像过程复杂而易产生伪影。
随着口腔修复技术、工艺的发展和人们经济条件的改善及口腔保健意识的提高,口腔临床上采用固定义齿修复的病例日益增多。然而由于固定义齿修复后口腔内金属材料的存在,在日后接受头颈部MRI检查时会使图像上产生磁敏感性伪影,干扰正常解剖结构和病变组织的显示,影响疾病的诊断。
目前临床常用的固定修复金属材料包括镍铬合金、钴铬合金、钛合金、纯钛、贵金属合金等;常用的金属固定修复体包括全冠、桩核、固定桥等。本文通过对目前临床常用的不同材料的金属全冠、不同材料的桩核、临床常用的两种金属材料的不同单位(长度)的固定修复体对MRI成像的影响进行调查研究,从而综合评价目前常用的不同材料的金属修复体、不同设计的金属修复体对MRI成像的影响,为今后临床修复设计及MRI检测的改进提供参考依据。
研究结果表明:
1.在T1加权GRE序列及相同的参数下,在金属固定修复体的外形大小、在人体口腔内的位置、定位方向均相同的情况下,金属固定修复体所产生的伪影的大小与其所采用的金属材料的种类相关,即与金属材料的组成有关,高贵金属产生的伪影较小,而钴铬合金则能产生很大的伪影。
2.在T1加权GRE序列及相同的参数下,金属固定修复体伪影的产生受到修复体在口腔内的位置、形状和金属的量的影响。
3.从MRI伪影的形成方面而言,预成钛桩树脂核是临床进行残根残冠修复的较好选择,但临床实际应用中,桩核外的最终修复体的选择也会对伪影的形成产生影响,需综合分析。
Preformed metal post and resin core are widely applied in the restoration of residual crowns and roots, which can simplify the process of restoration, reduce the incidence of dental root fracture and ensure adequate retention for the prosthesis in dental practice.
The proportion between the length of the post in the root and the root length plays an important role in the retention of post and core and in the avoidance of dental root fracture. Direct digital radiography helps ensure a perfect restoration by making the post in the optimal position of the root.
However, the images may be larger or smaller than the actual objects, which disturbs the precise placement of preformed metal posts, since direct digital radiography system can be influenced by many factors. In this study, the lengths of the preformed metal posts in the digital images were measured with software. Through comparing the measured length with the actual value, the distortion rate was calculated, which can provide valuable information to improve the clinical application of driect digital radiography.
The result is that the distortion rate of direct digital radiography in placement of preformed metal posts is high, and counter measures should be taken to minimize the distortion rate to reach the need for clinical applications.
MRI is one of the most valuable diagnostic tools for the examination of the head and neck regions in radiology and diagnostic sciences. However, in patients with metallic dental devices, artifacts due to misregistration at MR imaging can obscure normal anatomy or pathologic conditions and degrade the assessment quality of regions of interest near the devices.
The metallic materials widely used in dental practice include Nickel- chromium alloy, Cobalt-chromium alloy, Titanium, gold alloy, etc. The popular fixed prothesises consist of crown, post and core, fixed bridge and so on. This study was attempted to evaluate the artifacts caused by metallic materials of the fixed prothesis in MR imaging. Crowns and post-and-cores made of different metals, fixed prothesises with various units made of two types of metallic materials most popularly used in dental practice were imaged by means of 1.5T MRI apparatus in specific conditions.
This investigation could provide valuable information which conforms to the practice more than that of the previous studies concerning the artifacts caused by metallic dental devices in current use.
The main results are as follows:
1. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the types of metals of metallic devices. High noble metal alloys produce small artifacts, however, Cobalt-chromium alloys produce large artifacts.
2. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the size, on the shape, on the position in the oral cavity and on the amounts of the metals of metallic devices.
3. In the selection of the materials of fixed prothesis, in terms of the generation of the artifacts, preformed Titanium post resin core could be chosen to restore residual roots and crowns as one of the optimal materials, however, the effect of the fixed prothesises covering the post-and-core on MRI should be taken into account in dental practice.
预成金属桩根内桩长与根长的比例在适当的范围内(即2/3~3/4),对确保桩-核冠的固位和牙根的抗折力有重要的意义。初次植入预成桩后用口腔直接数字成像系统(Direct Digital Radiography,DDR)拍摄X线数字牙片(Digital Radiography),观测根内桩长与根长的比例,并对桩植入的深度加以校正,以达到最佳的植入深度、位置,从而可以获得理想的修复效果。
由于直接数字成像系统受到多种因素的影响,在临床中影像常被放大或缩小,影响对金属桩植入的判断。如何准确判断成像误差,成为需要关注的问题。本研究通过用测量软件在X线数字牙片上测量预成金属桩的长度,与实际长度比较,计算并考查口腔直接数字成像系统在预成金属桩植入应用中的失真率,以便为临床医生准确判读X线数字牙片及放射科改进拍摄技术提供参考。
研究结果表明:在临床预成金属桩植入中,通过现有常用方法获得的口腔直接数字成像根尖片具有很大的失真率,尚不能为预成金属桩的植入提供精确的指引,需要通过采取规范放射技师的拍摄技术等相应措施减小失真率以适合临床应用的需要,以期充分发挥口腔直接数字成像系统的优势。
MRI(Magnetic Resonance Imaging)是目前头颈部疾病最常用的影像学诊断设备之一,由于其多功能、多序列、多参数、多平面成像以及较高的软组织分辨力而被广泛应用于临床疾病的诊断与治疗。但由于其成像过程复杂而易产生伪影。
随着口腔修复技术、工艺的发展和人们经济条件的改善及口腔保健意识的提高,口腔临床上采用固定义齿修复的病例日益增多。然而由于固定义齿修复后口腔内金属材料的存在,在日后接受头颈部MRI检查时会使图像上产生磁敏感性伪影,干扰正常解剖结构和病变组织的显示,影响疾病的诊断。
目前临床常用的固定修复金属材料包括镍铬合金、钴铬合金、钛合金、纯钛、贵金属合金等;常用的金属固定修复体包括全冠、桩核、固定桥等。本文通过对目前临床常用的不同材料的金属全冠、不同材料的桩核、临床常用的两种金属材料的不同单位(长度)的固定修复体对MRI成像的影响进行调查研究,从而综合评价目前常用的不同材料的金属修复体、不同设计的金属修复体对MRI成像的影响,为今后临床修复设计及MRI检测的改进提供参考依据。
研究结果表明:
1.在T1加权GRE序列及相同的参数下,在金属固定修复体的外形大小、在人体口腔内的位置、定位方向均相同的情况下,金属固定修复体所产生的伪影的大小与其所采用的金属材料的种类相关,即与金属材料的组成有关,高贵金属产生的伪影较小,而钴铬合金则能产生很大的伪影。
2.在T1加权GRE序列及相同的参数下,金属固定修复体伪影的产生受到修复体在口腔内的位置、形状和金属的量的影响。
3.从MRI伪影的形成方面而言,预成钛桩树脂核是临床进行残根残冠修复的较好选择,但临床实际应用中,桩核外的最终修复体的选择也会对伪影的形成产生影响,需综合分析。
Preformed metal post and resin core are widely applied in the restoration of residual crowns and roots, which can simplify the process of restoration, reduce the incidence of dental root fracture and ensure adequate retention for the prosthesis in dental practice.
The proportion between the length of the post in the root and the root length plays an important role in the retention of post and core and in the avoidance of dental root fracture. Direct digital radiography helps ensure a perfect restoration by making the post in the optimal position of the root.
However, the images may be larger or smaller than the actual objects, which disturbs the precise placement of preformed metal posts, since direct digital radiography system can be influenced by many factors. In this study, the lengths of the preformed metal posts in the digital images were measured with software. Through comparing the measured length with the actual value, the distortion rate was calculated, which can provide valuable information to improve the clinical application of driect digital radiography.
The result is that the distortion rate of direct digital radiography in placement of preformed metal posts is high, and counter measures should be taken to minimize the distortion rate to reach the need for clinical applications.
MRI is one of the most valuable diagnostic tools for the examination of the head and neck regions in radiology and diagnostic sciences. However, in patients with metallic dental devices, artifacts due to misregistration at MR imaging can obscure normal anatomy or pathologic conditions and degrade the assessment quality of regions of interest near the devices.
The metallic materials widely used in dental practice include Nickel- chromium alloy, Cobalt-chromium alloy, Titanium, gold alloy, etc. The popular fixed prothesises consist of crown, post and core, fixed bridge and so on. This study was attempted to evaluate the artifacts caused by metallic materials of the fixed prothesis in MR imaging. Crowns and post-and-cores made of different metals, fixed prothesises with various units made of two types of metallic materials most popularly used in dental practice were imaged by means of 1.5T MRI apparatus in specific conditions.
This investigation could provide valuable information which conforms to the practice more than that of the previous studies concerning the artifacts caused by metallic dental devices in current use.
The main results are as follows:
1. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the types of metals of metallic devices. High noble metal alloys produce small artifacts, however, Cobalt-chromium alloys produce large artifacts.
2. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the size, on the shape, on the position in the oral cavity and on the amounts of the metals of metallic devices.
3. In the selection of the materials of fixed prothesis, in terms of the generation of the artifacts, preformed Titanium post resin core could be chosen to restore residual roots and crowns as one of the optimal materials, however, the effect of the fixed prothesises covering the post-and-core on MRI should be taken into account in dental practice.
引文
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63. Laakman RW, aufman B, Han JS, et al. MR imaging in patients with metallic implants [J]. Radiology, 1985, 157: 711-714
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65. Kazuyuki M, et a1. A Method of Reducing Susceptibility: Artifacts in MRI of the Head and Neck Region [J]. Oral Rsdiol,1996, 13(1):45-49.
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69. Camacho CR, Plewes DB, Henkelman RM. Nonsusceptibility artifacts due to metallic objects in MR imaging [J]. J Magn Reson Imag 1995, 5:75–88.
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74. Starcuk Z, Hubalkova H, Krupa P, et al. Assessment of MR compatibility of selected dental alloys [J]. Proc Int Soc Mag Reson Med 2005, 13: 2276.
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79. Davis PL, Crooks L, Arakawa M, et al. Potential hazards in NMR imaging: heating effects of changing magnetic fields and RF fields on small metallic implants [J]. AJR 1981, 137: 857–860.
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83. Fiala TG, Novelline RA, Yaremchuk MJ. Comparison of CT imaging artifacts from craniomaxillofacial internal fixation devices [J]. Plast Reconstr Surg, 1993, 92: 1227–1232
84. Kaneda T, Minami M, Curtin HD, et al. Dental burr fragments causing metal artifacts on MR images [J]. AJNR Am J Neuroradiol, 1998, 19: 317–319.
85. Abbaszadeh K, Heffez LB, Mafee MF. Effect of interference of metallic objects on interpretation of T1-weighted magnetic resonance images in the maxillofacial region. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 2000, 89: 759–765.
86. Graf H, Klemm T, Lauer UA, et al. Systematics of imaging artifacts in MRIcaused by metallic vascular implants (stents). Rofo, 2003, 175: 1711–1719
87. Gray CF, Redpath TW, Smith FW, et al. Advanced imaging: magnetic resonance imaging in implant dentistry. Clin Oral Implants Res, 2003, 14: 18–27