Metallic artifact in MRI after removal of orthopedic implants

Objective

The aim of the present study was to evaluate the metallic artifacts in MRI of the orthopedic patients after removal of metallic implants.

Subjects and methods

From March to August 2009, 40 orthopedic patients operated for removal of orthopedic metallic implants were studied by post-operative MRI from the site of removal of implants. A grading scale of 0–3 was assigned for artifact in MR images whereby 0 was considered no artifact; and I–III were considered mild, moderate, and severe metallic artifacts, respectively. These grading records were correlated with other variables including the type, size, number, and composition of metallic devices; and the site and duration of orthopedic devices stay in the body.

Results

Metallic susceptibly artifacts were detected in MRI of 18 of 40 cases (45%). Screws and pins in removed hardware were the most important factors for causing artifacts in MRI. The artifacts were found more frequently in the patients who had more screws and pins in the removed implants.Gender, age, site of implantation of the device, length of the hardware, composition of the metallic implants (stainless steel versus titanium), and duration of implantation of the hardware exerted no effect in producing metallic artifacts after removal of implants. Short TE sequences of MRI (such as T1 weighted) showed fewer artifacts.

Conclusion

Susceptibility of metallic artifacts is a frequent phenomenon in MRI of patients upon removal of metallic orthopedic implants.     

髋关节外伤螺旋CT重建技术的应用

目的：探讨螺旋CT多平面重建(MPR)、三维表面遮盖法重建(SSE))及容积再现(VR)在髋臼骨折及股骨头脱位中的临床应用价值。方法：对25例髋关节外伤的患者进行螺旋CT容积扫描，然后在工作站上进行MPR、SSD、VR成像，结合轴位扫描图像，观察这三种重建图像在显示骨折线、骨碎片以及股骨头脱位方向和程度的效果。结果：MPR对判断股骨头的脱位方向和程度有帮助；SSD显示髋臼骨折和股骨头脱位的立体效果较好；VR虽然立体效果稍逊于SSD．但能显示骨折的细微结构。结论：MPR、SSD、VR三种重建方法可互为补充，能够立体直观、整体地显示髋臼骨折和股骨头脱位．为决定治疗方案和选择适当的手术入路提供了依据.     

MR螺旋桨扫描技术在消除伪影方面的临床应用

目的探讨螺旋桨扫描技术（periodically rotated overlapping parallel lines enhanced reconstruction，PROPELLER）在临床的应用价值。方法对10例健康志愿者在头部晃动状态下、64例头颅MR检查中出现躁动不合作或口腔有固定金属异物的患者，应用PROPELLER技术进行T2WI和（或）扩散加权成像（DWI），与常规T2WI和（或）DWI进行对比。64例患者中，脑梗死40例（其中脑干梗死16例），脑梗死伴脑出血1例，脑转移瘤3例，癫痫、病毒性脑炎和高血压等20例。56例为运动伪影，8例为金属异物引起的磁敏感伪影。结果10例健康志愿者PROPELLER T2W图像质量明显优于常规T2WI。分别对10例志愿者和56例患者的常规T2WI、DWI与PROPELLER T2WI、DWI的图像进行比较，显示因运动产生的伪影，导致图像质量降低，无法达到诊断要求；采用PROPELLER T2WI，均显著消除伪影的影响，病变显示清晰，诊断明确。8例因固定义齿产生的磁敏感伪影，采用PROPELLER DWI，均明显消除伪影干扰，获得有诊断价值的图像。结论应用PROPELLER T2WI、DWI技术，明显消除患者因运动或金属异物造成的伪影，可生成高分辨率、无伪影、具有临床诊断意义的理想图像。     

MR imaging and metallic implants for anterior cruciate ligament reconstruction: assessment of ferromagnetism and artifact.

Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.     

Does reducing CT artifacts from dental implants influence the PET interpretation in PET/CT studies of oral cancer and head and neck cancer?

In patients with oral head and neck cancer, the presence of metallic dental implants produces streak artifacts in the CT images. These artifacts negate the utility of CT for the spatial localization of PET findings and may propagate through the CT-based attenuation correction into the PET images. In this study, we evaluated the efficacy of an algorithm that reduces metallic artifacts in CT images and the impact of this approach on the quantification of PET images. METHODS: Fifty-one patients with and 9 without dental implants underwent a PET/CT study. CT images through the patient's dental implants were reconstructed using both standard CT reconstruction and an algorithm that reduces metallic artifacts. Attenuation correction factors were calculated from both sets of CT images and applied to the PET data. The CT images were evaluated for any reduction of the artifacts. The PET images were assessed for any quantitative change introduced by metallic artifact reduction. RESULTS: For each reconstruction, 2 regions of interest were defined in areas where the standard CT reconstruction overestimated the Hounsfield units (HU), 2 were defined in underestimated areas, and 1 was defined in a region unaffected by the artifacts. The 5 regions of interest were transferred to the other 3 reconstructions. Mean HU or mean Bq/cm(3) were obtained for all regions. In the CT reconstructions, metallic artifact reduction decreased the overestimated HUs by approximately 60% and increased the underestimated HUs by approximately 90%. There was no change in quantification in the PET images between the 2 algorithms (Spearman coefficient of rank correlation, 0.99). Although the distribution of attenuation (HU) changed considerably in the CT images, the distribution of activity did not change in the PET images. CONCLUSION: Our study demonstrated that the algorithm can enhance the structural and spatial content of CT images in the presence of metallic artifacts. The CT artifacts do not propagate through the CT-based attenuation correction into the PET images, confirming the robustness of CT-based attenuation correction in the presence of metallic artifacts. The study also demonstrated that considerable changes in CT images do not change the PET images.     

Metal artifact reduction image reconstruction algorithm for CT of implanted metal orthopedic devices: a work in progress

Introduction  Despite recent advances in CT technology, metal orthopedic implants continue to cause significant artifacts on many CT exams, often obscuring diagnostic information. We performed this prospective study to evaluate the effectiveness of an experimental metal artifact reduction (MAR) image reconstruction program for CT. Materials and methods  We examined image quality on CT exams performed in patients with hip arthroplasties as well as other types of implanted metal orthopedic devices. The exam raw data were reconstructed using two different methods, the standard filtered backprojection (FBP) program and the MAR program. Images were evaluated for quality of the metal–cement–bone interfaces, trabeculae ≤1 cm from the metal, trabeculae 5 cm apart from the metal, streak artifact, and overall soft tissue detail. The Wilcoxon Rank Sum test was used to compare the image scores from the large and small prostheses. Interobserver agreement was calculated. Results  When all patients were grouped together, the MAR images showed mild to moderate improvement over the FBP images. However, when the cases were divided by implant size, the MAR images consistently received higher image quality scores than the FBP images for large metal implants (total hip prostheses). For small metal implants (screws, plates, staples), conversely, the MAR images received lower image quality scores than the FBP images due to blurring artifact. The difference of image scores for the large and small implants was significant (p = 0.002). Interobserver agreement was found to be high for all measures of image quality (k > 0.9). Conclusion  The experimental MAR reconstruction algorithm significantly improved CT image quality for patients with large metal implants. However, the MAR algorithm introduced blurring artifact that reduced image quality with small metal implants.     

Computed tomographic metal artifact reduction for the detection and quantitation of small features near large metallic implants: a comparison of published methods

Computed tomographic imaging of tissue surrounding metallic implants is often limited by metal artifacts. This paper compares 3 existing metal artifact reduction techniques that are based on segmentation of metal-affected regions in native images, followed by reprojection of segmented areas into original Radon space, removal of metal trace(s), and renewed reconstruction: Detector row-wise linear interpolation, 2-dimensional interpolation, and combination of row-wise linear interpolation and adaptive filtering. For each method, improvements of CT number accuracy and signal-noise as well as contrast-noise ratios near the prosthesis and in the image periphery over the values found for native images were evaluated in a phantom experiment simulating osteolytic bone lesions of different size and density around a Chrome-Cobalt hip prosthesis stem. Improvement in diagnostic usability was evaluated as lesion detectability by size. Quantitative and qualitative results showed that the linear interpolation and the combination method removed the artifacts most effectively. The mean accuracy error over different regions of interest placed in the direct vicinity of the metal and in the periphery of the object decreased 10-fold with linear interpolation. These methods increased contrast-noise ratio up to 68% of that measured on artifact-free images for the least dense lesion. Qualitatively, the linear interpolation and the combination method improved the lesion detectability and enabled differentiation of different lesion densities. However, in proximity to the stem, some artifacts remained for all methods. We conclude that published algorithms for metal artifact reduction substantially improve image quality for CT imaging of a metallic object and may be adequate for quantitative measurements except for the direct vicinity of the metallic object.     

迭代重建在膝关节置换术后X线数字化断层融合检查中的应用价值

目的：探讨 X 线数字化断层融合（DTS）运用迭代重建技术（IR）,降低膝关节图像金属植入物伪影的可行性和临床应用价值。方法：79例人工膝关节置换术后患者行 DTS 扫描,分别采用滤波反投影重建（FBP）技术和迭代重建（IR）技术对原始图像进行重建。从图像清晰度、假体金属植入物与周围骨相连结构的显示度、金属伪影的多少等方面对两组图像进行分析并评价。根据骨科临床对人工膝关节的分区,在后处理工作站上测量 A1～A7区域内假体与骨之间硬化束金属伪影的长度。结果：对两种重建技术所得到的图像进行主观评价,IR 组优片率为88．6％,FBP 组优片率为62％, IR 组优片率高于 FBP 组,差异有统计学意义（P ＜0．05）。IR 组重建图像在 A1、A3～A7区域无金属伪影,仅3例图像 A2区域见少许金属伪影,A7区域关节间隙内聚氨酸脂软垫显示清晰;FBP 组人工假体在 A1～A7区域均见金属伪影,伪影长度为0．5～2．6 mm。FBP 组图像伪影明显多于 IR 组。结论：有金属植入物的人工膝关节置换术后患者行 DTS 检查,运用 IR 技术可明显减少金属植入物伪影,图像质量明显改善,在术后随访中具有较高的临床应用价值。     

多层螺旋CT重建参数对头颈部肿瘤MPR图像质量的影响

目的　分析多层螺旋CT(MSCT)重建及重组参数对头颈部肿瘤MPR图像质量的影响 ,以便选择最佳的参数组合。资料与方法　使用GELightspeedUltra 8层螺旋CT扫描机对 6 7例头颈部肿瘤患者进行扫描。分为两部分 ,第一部分 2 8例 ,分别对原始数据进行 1.2 5mm、2 .5mm层厚的轴面重建 ,重叠率均为 5 0 %。图像重组时 ,分别采用层厚 1mm、2mm、3mm和 5mm。第二部分 39例 ,分别采用 0 %、2 5 %、5 0 %和 75 %的重叠率和 1.2 5mm层厚进行轴面重建 ,然后采用 1mm层厚进行图像重组。应用双盲法评价各组图像质量 ,并进行统计学处理。结果　第一部分 ,在软组织、骨质和伪影方面组内差异有极显著性 (P <0 .0 1) ,1.2 5mm层厚轴面重建的各组MPR图像中 ,1mm层厚组对软组织和骨质的显示好于其他各组 (P <0 .0 1)。第二部分 ,在软组织、病变、骨质和伪影方面组内差异有极显著性 (P <0 .0 1) ;在软组织和病变方面 ,5 0 %与 75 %重叠率图像质量最佳 ,两者差异无显著性 (P >0 .0 5 ) ;在骨质方面 75 %重叠率组图像质量高于 5 0 %组 (P <0 .0 5 ) ;在伪影方面 ,5 0 %重叠率组好于 75 %组 (P <0 .0 1)。结论　头颈部肿瘤MSCT图像后处理采用 1.2 5mm层厚、5 0 %重叠率进行轴面重建后 ,用 1mm层厚的MPR图像能很好地显示软组织、病变     

MRI in ACL reconstructive surgery with PDLLA bioabsorbable interference screws: evaluation of degradation and osteointegration processes of bioabsorbable screws

PURPOSE: Anterior cruciate ligament (ACL) reconstructive surgery has seen significant progress since bioabsorbable interference screws have replaced synthetic metallic screws for ligament graft fixation within the femoral and tibial osseous tunnel. Our study compared the MR images of patients who underwent ACL reconstruction using bioabsorbable interference screws with those of patients who underwent ACL reconstruction using metallic screws to evaluate the MR aspects of degradation and osteointegration processes of bioabsorbable interference screws post-operatively. MATERIALS AND METHODS: Between September 1999 and December 2002 we performed MRI on 40 patients who underwent arthroscopic ACL reconstruction with patellar tendon auto-graft using PDLLA bioabsorbable screws in 35 cases and metallic screws in 5 cases. After surgery, all patients underwent an intensive rehabilitation programme along with clinical evaluation using the standard knee ligament evaluation form of the International Knee Documentation Committee (IKDC) and radiological examinations. MR studies were performed 1, 2 and 3 years post-operatively using a 0.5-Tesla MR scanner with T1- and T2*-weighted and STIR sequences. RESULTS: Thirty-three patients were clinically classified as group A IKDC (full return to sports activity) and 7 patients as group B IKDC. No foreign-body reaction was found in patients treated with bioabsorbable interference screws, both from a clinical point of view and from laboratory exams. Ferromagnetic artefacts were found in all patients treated with metallic interference screws. In patients with bioabsorbable interference screws, degradation of the screws and absence of significant artefacts allowed correct evaluation of the signal of the reconstructed ligament throughout its length, the osseous tunnels and the joint cavity. In 34 of 35 patients with bioabsorbable interference screws, the screw could not be detected due to complete degradation. In 8, 12 and 4 cases, a small cyst-like formation due to screw hydrolysis was present at the screw site within 1, 2 and 3 years from surgery respectively. Only in 4 cases was the process of osteointegration of the screw and bone plug complete 3 years after the operation, with consequent restoration of bone morphology. DISCUSSION AND CONCLUSIONS: The use of bioabsorbable interference screws is a valuable alternative to synthetic metallic fixation implants as the absence of artefacts allows correct post-operative MR follow-up. MRI is the only technique able to visualize all the portions of the transplant and to evaluate the healing process. Bioabsorbable interference screws usually degrade within one year. However, full osteointegration requires a long time and may not be complete 3 years after surgery. The presence of cyst-like formations at the screw site has to be regarded as a normal feature of the screw degradation process. Therefore, the use of bioabsorbable interference screws is recommended as it enables MR follow-up of the knee after ACL reconstruction.     

CT能谱成像在消除金属移植物伪影中的应用价值

目的 探讨CT能谱成像(GSI)中单能量图像消除金属移植物硬化伪影的作用.方法 对体内有金属移植物的患者行GSI.其中义齿3例、颈椎钢板植入2例、锁骨钢板植入1例、腰椎金属棒植入1例、人工股骨头3例、髂骨骨折移植物1例、胫骨钢板植入1例.对上述部位行GSI螺旋扫描,管电压采用80 kVp和140 kVp,在0.5 ms内行快速切换扫描.然后重建1.25 mm层厚能谱图像,含40～140 keV共101个单能图像,不同keV单能图像均采用同样的窗宽(1500 HU)、窗位(500HU).测量不同keV单能量图像的伪影指数(AI),分析不同单能量图像伪影消除程度,将AI最小的单能keV图像保存,应用于三维重组.结果 单能图像中AI随keV变化而不同,12例中最大AI为145～225,均在40keV时出现;最小AI为15～190,出现在95～140 keV之间.重组图像时,12例常规的混合能量图像均有明显的金属伪影,用最小AI的单能量图像重建时,可明显肖除或降低金属移植物的硬化伪影.结论 采用CT能谱成像技术,在高keV单能量图像上可以明显降低或消除金属移植物伪影,改善图像质量.     

CT of metal implants: reduction of artifacts using an extended CT scale technique

PURPOSE: The purpose of this work was to use an extended CT scale technique (ECTS) to reduce artifacts due to metal implants and to optimize CT imaging parameters for metal implants using an experimental model. METHOD: Osteotomies were performed in 20 porcine femur specimens. One hundred cobalt-base screws and 24 steel plates were used for osteosynthesis in these specimens. Artificial lesions were produced in 50 screws, such as osteolysis near the screws (mimicking lysis due to infection, tumor, or loosening), displacement of the screws, as well as fractures of the screws. All specimens were examined using eight different CT protocols: four conventional (CCT) and four spiral (SCT) CT protocols with different milliampere-second values (130 and 480 mAs for CCT, 130 and 300 mAs for SCT), kilovolt potentials (120 and 140 kVp), and slice thicknesses (2 and 5 mm). The images were analyzed by three observers using a standard window (maximum window width 4,000 HU) and ECTS (maximum window width 40,000 HU). Receiver operating characteristic analysis was performed, and image quality was assessed according to a five level scale. RESULTS: Metal artifacts were significantly reduced using ECTS (p < 0.05). The highest diagnostic performance was obtained using ECTS with the thinnest slice thickness. Metal artifacts were more pronounced using SCT. In this experimental model, exposure dose and kilovolt potential had no significant impact on diagnostic performance (p > 0.05). CONCLUSION: ECTS improved imaging of metal implants. In this study, no significant effects of exposure dose and kilovolt potential were noted. Metal artifacts were more prominent using SCT than using CCT.     

螺旋CT多平面重建对临床不典型阑尾炎的诊断价值

目的:探讨螺旋CT多平面重建(MPR)对无典型临床表现阑尾炎的诊断价值.方法:搜集临床首次诊断未考虑为阑尾炎,手术和病理证实为阑尾炎者19例,回顾性分析比较螺旋CT轴扫和多平面重建(MPR)两种方法的诊断符合率.结果:8例表现为阑尾增粗、壁增厚并有明显强化,其中4例阑尾内见结石;盲肠和(或)周围炎10例;右下腹局限性脓肿5例,其中2例伴斑点钙化.采用螺旋CT轴扫法误诊为回盲部及升结肠肿瘤2例,盆腔炎1例,误诊率15.8%,诊断符合率84.2%.采用螺旋CT多平面重建法误诊为回盲部及升结肠肿瘤1例,误诊率5.3%,诊断符合率94.7%.结论:症状和体征不典型的阑尾炎临床诊断困难,易误诊,螺旋CT MPR方法简单,可从不同角度观察病变部位及其周围情况,有利于鉴别诊断,提高诊断符合率,具有较高的临床价值.     

多层螺旋CT不同重建方法在骨关节创伤中的应用价值比较

目的 比较多层螺旋CT(MSCT)不同重建方法在骨关节创伤中的应用价值。资料与方法 51例创伤患者，全部行伤患处薄层螺旋CT横断面扫描及MPR、VR、SSD重建，分析比较几种方法重建图像对各部位骨折或脱位的显示效果。结果 颅面骨创伤3例，颈椎6例，肩关节6例，肘关节5例，膝关节10例，踝关节9例，骨盆12例。横断面扫描显示出骨折及脱位50例(98．0％)，SSD重建明确诊断47例(92．2％)，VR重建明确诊断49例(96．1％)，MPR重建均获明确诊断。图像显示横断面扫描可发现细小骨折但缺乏立体信息，3D重建立体感强，可多角度、多方位观察，骨折移位及关节脱位情况一目了然；MPR法显示骨折线的走行和移位更有优势且能兼顾软组织改变。结论 MSCT几种重建方法各有优势，应以横断面扫描信息为基础，根据部位及伤情结合以MPR、SSD、VR中的一种或几种，为临床诊治及随访提供全面、精确而直观的信息。     

多层螺旋CT及重建技术在胸部创伤中的临床应用

目的:讨论多层螺旋CT(MSCT)扫描及重建技术在胸部创伤中的临床应用价值。方法:57例胸部创伤病人行MSCT扫描,重建层厚2.5 mm,间隔1.25 mm,将数据传至专门工作站,对骨性胸廓进行多平面重建(MPR)、薄层最大密度投影(STS-MIP)及容积再现(VR)重建,对横断面图像及重建图像进行回顾性分析。结果:57例胸部创伤患者中,发现肺挫伤44例,肺撕裂伤4例,肺不张及肺萎缩11例,气胸27例,胸腔积液42例,肋骨骨折36例,肋软骨骨折2例,肩胛骨骨折6例,锁骨骨折3例,胸椎骨折1例。MPR图像可清楚显示骨折线的走行及移位,3D重建图像从各个方位显示了骨折的空间改变。结论:多层螺旋CT扫描能够清晰显示肺部损伤情况,胸廓重建图像可以显示骨折的立体空间改变,两者相结合,对临床制定治疗方案具有重要的参考价值。     

螺旋CT横断扫描及重建对肩关节创伤的临床应用研究

目的:探讨螺旋CT横断扫描及重建技术(SSD、MPR)在肩关节创伤中的临床应用价值及技术特点。方法:回顾性分析我院收治经X线、CT、SSD和MPR证实的肩关节外伤57例及正常对照组40例。SSD和MPR以横断面螺旋CT扫描图像为基础,层厚3-5mm,螺距1-1.5,重建间距1-2mm。结果:SSD、MPR图像质量与扫描参数的选择及重建间距密切相关,SSD及MPR图像均能更好地显示骨折,并可立体地显示骨折线的长短、形态、走向,碎骨片的形态、大小、空间位置以及骨折的移位和关节对位情况。结论:螺旋CT扫描及重建技术对肩关节的骨折、脱位或半脱位可提供有价值的空间关系信息,利于临床医师选择治疗方案和制订手术计划。     

Magnetic resonance imaging of in vivo kinematics after total knee arthroplasty

PURPOSE: To improve the quality of magnetic resonance imaging (MRI) on knees after total knee arthroplasty (TKA) by minimizing image artifacts caused by metallic implants, and to establish a method determining in vivo kinematics of TKA knees using MRI. MATERIALS AND METHODS: Two knee implants made of cobalt-chrome and oxidized zirconium were tested with different pulse sequences and imaging parameters. Then, in vivo kinematic MRI was performed on five well-functioning TKAs under simulated weight-bearing conditions. Kinematic measurements were made and a linear correlation test was run between the tibio- and patellofemoral measurements. RESULTS: The best images with minimum metallic artifacts were observed using oxidized zirconium implants, a fast spin echo sequence (FSE), thin slice thickness, and high readout gradient. TKA kinematics exhibited a large deviation from the normal kinematics and considerable patient-to-patient variability. However, significant linear correlations between tibiofemoral and patellofemoral kinematics were observed (R = -0.96, 0.92, 0.88). CONCLUSION: Metallic artifacts due to orthopedic implants can be reduced in MR images for some materials, appropriate pulse sequence, and imaging parameters selection, enabling MR quantification of knee kinematics. Tibiofemoral kinematics appears to affect patellofemoral position after total knee arthroplasty.     

Evaluation of CT techniques for reducing artifacts in the presence of metallic orthopedic implants

Metallic intramedullary orthopedic implants generate artifacts that can markedly degrade transaxial CT images. The artifacts, typically seen as starburst streaking, result primarily from reconstructions involving missing projection data. Two approaches are clinically available to reduce the artifacts around orthopedic implants. These are (a) the imaging of implants with lower attenuation coefficients or smaller path lengths (less attenuating objects) and (b) the planar reformatting of image data. The sizing accuracy of these two approaches was quantified using phantoms and the efficacy using cadaveric femoral specimens. Results demonstrated that metal artifacts may be reduced and accurate bony dimensional data obtained.     

矫形金属植入物CT扫描技术的初步经验

目的:该项研究通过改变矫形金属植入物MSCT扫描和重建方案的实验,以获得影像诊断质量满意的最佳检查方案.方法:取尸体标本采用MSCT扫描,扫描野25 cm;观查野10 cm;扫描时间1.0 s其它参数分别为(80;20 kV.80;400 mA.Pitch值1.75;0.75.扫描层厚5;0.5 mm.影像数据取60%叠加重组.进行不同摆位和参数的试验.结果:改变摆位或扫描架角度,可将金属植入物在扫描层面的量减至最小,降低了线束硬化伪影.提高kVp,mAs值,减小扫描和重组层厚以及Pitch值,可提高信噪比,两者均可抹消部分金属伪影.结论:MDCT取上述实验的最佳检查方案可显著抹消部分金属伪影.     

Slice encoding for metal artifact correction with noise reduction

Magnetic resonance imaging (MRI) near metallic implants is often hampered by severe metal artifacts. To obtain distortion‐free MR images near metallic implants, SEMAC (Slice Encoding for Metal Artifact Correction) corrects metal artifacts via robust encoding of excited slices against metal‐induced field inhomogeneities, followed by combining the data resolved from multiple SEMAC‐encoded slices. However, as many of the resolved data elements only contain noise, SEMAC‐corrected images can suffer from relatively low signal‐to‐noise ratio. Improving the signal‐to‐noise ratio of SEMAC‐corrected images is essential to enable SEMAC in routine clinical studies. In this work, a new reconstruction procedure is proposed to reduce noise in SEMAC‐corrected images. A singular value decomposition denoising step is first applied to suppress quadrature noise in multi‐coil SEMAC‐encoded slices. Subsequently, the singular value decomposition‐denoised data are selectively included in the correction of through‐plane distortions. The experimental results demonstrate that the proposed reconstruction procedure significantly improves the SNR without compromising the correction of metal artifacts. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.