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OBJECTIVE@#To propose a framework that combines sinogram interpolation with unsupervised image-to-image translation (UNIT) network to correct metal artifacts in CT images.@*METHODS@#The initially corrected CT image and the prior image without artifacts, which were considered as different elements in two different domains, were input into the image transformation network to obtain the corrected image. Verification experiments were carried out to assess the effectiveness of the proposed method using the simulation data, and PSNR and SSIM were calculated for quantitative evaluation of the performance of the method.@*RESULTS@#The experiment using the simulation data showed that the proposed method achieved better results for improving image quality as compared with other methods, and the corrected images preserved more details and structures. Compared with ADN algorithm, the proposed algorithm improved the PSNR and SSIM by 2.4449 and 0.0023 when the metal was small, by 5.9942 and 8.8388 for images with large metals, and by 8.8388 and 0.0130 when both small and large metals were present, respectively.@*CONCLUSION@#The proposed method for metal artifact correction can effectively remove metal artifacts, improve image quality, and preserve more details and structures on CT images.
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Artifacts , Algorithms , Computer Simulation , Tomography, X-Ray ComputedABSTRACT
OBJECTIVE@#To propose an adaptive weighted CT metal artifact reduce algorithm that combines projection interpolation and physical correction.@*METHODS@#A normalized metal projection interpolation algorithm was used to obtain the initial corrected projection data. A metal physical correction model was then introduced to obtain the physically corrected projection data. To verify the effectiveness of the method, we conducted experiments using simulation data and clinical data. For the simulation data, the quantitative indicators PSNR and SSIM were used for evaluation, while for the clinical data, the resultant images were evaluated by imaging experts to compare the artifact-reducing performance of different methods.@*RESULTS@#For the simulation data, the proposed method improved the PSNR value by at least 0.2 dB and resulted in the highest SSIM value among the methods for comparison. The experiment with the clinical data showed that the imaging experts gave the highest scores of 3.616±0.338 (in a 5-point scale) to the images processed using the proposed method, which had significant better artifact-reducing performance than the other methods (P < 0.001).@*CONCLUSION@#The metal artifact reduction algorithm proposed herein can effectively reduce metal artifacts while preserving the tissue structure information and reducing the generation of new artifacts.
Subject(s)
Algorithms , Artifacts , Image Processing, Computer-Assisted/methods , Metals , Phantoms, Imaging , Tomography, X-Ray Computed/methodsABSTRACT
Objective:To evaluate the metal artifacts reduction effect of multi-acquisition variable-resonance image combination (MAVRIC-SL) after total knee arthroplasty by comparing with two-dimensional fast spin-echo metal artifact reduction sequence (2D FSE MARS).Methods:A total of 78 patients (101 knees) who underwent total knee arthroplasty in Beijing Tsinghua Changgung Hospital from December 2018 to December 2020 were prospectively collected. All patients underwent 3.0 T MR examination within 2 weeks after surgery. The sequences included axial, sagittal, and coronal 2D FSE MARS and MAVRIC-SL. The ranges of prosthesis artifacts were measured, and the scores of the prosthesis clarity, anatomical structure clarity, and joint effusion diagnosis confidence were evaluated by Likert scale. Paired t test was used to compare the difference of artifact range between 2D FSE MARS and MAVRIC-SL. The Wilcoxon signed rank-sum test was used to compare image quality scores and joint effusion diagnosis confidence scores. Results:In 101 knees, the ranges of prosthesis artifacts in axial, sagittal, and coronal 2D FSE MARS were (63.3±8.5), (60.0±7.4) and (62.1±8.7) cm 2, while those of MAVRIC-SL were (49.5±5.8), (44.1±6.6) and (46.1±7.5) cm 2. The differences were statistically significant ( t=20.021, 21.834, 25.472, all P<0.001). The subjective scores of femoral prosthesis clarity, tibial prosthesis clarity, and anatomical structure clarity of MAVRIC-SL were significantly higher than those of 2D FSE MARS (all P<0.001). Confidence scores of 2D FSE MARS and MAVRIC-SL for diagnosing joint effusion were 2 (1, 3) and 3 (2, 3), respectively, and the difference was statistically significant ( Z=6.549, P<0.001). Conclusion:Compared with 2D FSE MARS, MAVRIC-SL can further reduce the metal artifacts in total knee arthroplasty and improve the diagnostic confidence of joint effusion.
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Objective:To explore the value of metal artifact reduction in oblique sagittal multi-acquisition with variable resonance image combination slab selectivity (MAVRIC-SL) inversion recovery (IR) sequence compared with conventional fast spin-echo (FSE) fat saturation (FS)-T 2WI and proton density weighted imaging (PDWI) on the postoperative review of patients with metal-fixed anterior cruciate ligament reconstruction (ACLR) at 3.0 T MR. Methods:From June to November 2018, 27 patients with metal fixtures in ACLR were prospectively recruited in the First Hospital of China Medical University. The FSE sequences (FS-T 2WI and PDWI) and the MAVRIC-SL IR were performed at 3.0 T MRI system. The maximum artifact slice was selected and ROI was drawn, then the implant and artifact area and the number of artifact-influence slices were recorded. Image signal-to-noise ratio (SNR) was calculated. The degree of image artifacts (artifact degree of spiked ligament staple and its influence on the diagnosis of surrounding structures), measurability (measurability of distance between the upper edge of the staple and the lower edge of the graft entrance on tibia), and other degree of artifacts (whether there were metal artifacts other than implants that affect the observation of other structures within the scanning range) were scored. The Friedman M test and pairwise comparison were used to compare and analyze the quantitative and qualitative data. Results:The differences in artifact area, the number of artifact-influence slices and SNR among FS-T 2WI, PDWI and MAVRIC-SL IR images were statistically significant (all P<0.001). Pairwise comparison analysis suggested that the metal implant artifact area and the number of artifact-influence slices in the MAVRIC-SL IR image were smaller, and the SNR was higher than those of FS-T 2WI and PDWI (all P<0.05 after correction). The differences of the three scores among FS-T 2WI, PDWI and MAVRIC-SL IR were statistically significant (all P<0.001). Pairwise comparison analysis suggested that the degree of image artifacts score of MAVRIC-SL IR sequence was lower, and the measurability and other degree of artifacts scores were higher than FS-T 2WI and PDWI (all P<0.05 after correction). Conclusion:MAVRIC-SL can significantly reduce the metal artifacts and improve image quality in the postoperative MRI review of the patients with metal-fixed ACLR. Therefore, oblique sagittal MAVRIC-SL IR sequence can be used for assisting the diagnosis of conventional FS-T 2WI and PDWI.
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Objective:To evaluate spectral CT metal artifacts reduction (MAR) technique in reducing metal artifacts of spinal implants in a phantom.Methods:Ovine spines were chosen as anthropomorphic phantom. The phantom including the pedicle screws, 3D-printed vertebral body (VB) and mesh cage were examined using spectral CT. Postoperative CT images were reconstructed at 70—140 keV with 10 keV interval of MAR and non-MAR. Artifact index (AI) and signal-to-noise ratio (SNR) were evaluated by CT and SD values in ROIs around the implants. Visibility of bony structures, the artifacts of pedicle screw, 3D-printed VB and mesh cage were subjectively evaluated. Plotting curves of AI and SNR with the increasing keV were drawn. The AI and SNR were compared at lower (70 keV), medium (100 keV) and high (130 keV) level between MAR and non-MAR images using the paired t-test, and the subjective scores were compared using Wilcoxon signed rank-sum test. Results:The AI values around pedicle screws (anterior, posterior and lateral), 3D-printed VB and mesh cage decreased with the increase of keV, while SNR improved in MAR and non-MAR images. The AI values in the anterior, lateral and posterior pedicle screws and lateral titanium implants were significantly lower in MAR than those in non-MAR ( P<0.05). The AI value in posterior 3D-printed vertebral was lower in MAR than that of non-MAR only at 70 keV ( P<0.001). The SNR values in the anterior and posterior pedicle screws, 3D-printed VB increased with the increase of keV, but decreased in other ROIs. In the subjective evaluation, the image scores of MAR were higher than those of non-MAR ( P<0.05). Conclusion:Spectral CT using the MAR reconstruction can effectively reduce metal artifacts of spinal implants. The effect is better in pedicle screw and mesh cage than 3D-printed VB.
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OBJECTIVE@#To explore the application value of MAR algorithm in metal artifact removal of CT simulator.@*METHODS@#CT phantom with titanium plate was scanned using conventional algorithms and MAR algorithms, respectively. Artifact index(AI), contrast-to-noise ratio(CNR) and AI values at different slices were used to analyze the artifact images.@*RESULTS@#In artifact index, MAR algorithm (10.28±2.60) is significantly lower than conventional algorithm (20.65±5.04); In contrast-to-noise ratio index, MAR algorithm (7.81±1.12) is better than conventional algorithm (5.61±1.36). The above indicators were statistically significant in both algorithms (P<0.01). In the slices affected by metal artifacts, the artifact index decreased by 21.72%~88.40% after the MAR algorithm.@*CONCLUSIONS@#MAR algorithm can significantly reduce the metal artifacts and improve the clinical value of CT data.
Subject(s)
Algorithms , Artifacts , Metals , Phantoms, Imaging , Titanium , Tomography, X-Ray ComputedABSTRACT
Objective To study the optimum programme of monoenergetic imaging technology of dual-source CT in visualization for patients with chest trauma and fractures fixed with metal fixator.Methods Fifty patients with fractures by chest trauma fixed with metal fixator were selected as research subjects.Subjects were divided into 5 groups randomly,10 in each group.Each group underwent dual-source CT scanning:Group A,supine position+CARE Dose4D+80/SN 140 kV check;Group B,supine position+80/SN 140 kV check;Group C,supine position+ CARE Dose4D+100/SN 140 kV check;Group D,supine position+ CARE Dose4D+ 140/80 kV check;Group E,semireclining position+CARE Dose4D+80/SN 140kV check.The volume CT dose index(CTDIvol),dose length product(DLP)and effective dose(ED)of each group were compared.Three fixators were selected from each patient randomly.Then the monoenergetic curve analysis was carried out on the acquisition data to obtain the minimum CT differential energy points,and meanwhile the biggest area of low density artifacts(S,cm2)of the fixators and the contrast to noise ratio(CNR)of overall image were calculated.The quality of images was subjectively graded by a 4-score scale.Results The CTDIvol,DLP and ED were signifi-cantly lower in group E than that in group B,C and D,and slightly lower than that in group A.The quality of images and the area of low density artifacts(S)in group E were better than that in group A,B,C,and D.There were no differences in CNR between group E and group A,B and C,but better than that in group D.Conclusion The use of semireclining position,CARE Dose4D,combined with 80/SN 140 kV tube voltage.And then the use of analyzation of monoenergetic curves to define the optimum monoenergetic point rapidly when reprocess,allow for significant dose reduction and the best personalized image for chest trauma fixed with metal fixator.
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Objective To investigate the feasibility of reducing spine metal artifacts with metal artifacts reduction technique (WARP) at 3.0 T MRI.Methods This study included 15 cervical and 14 lumbar spine cases.The image quality of WARP sequences and conventional sequences were compared (5 score evaluation scale) as well as the signal to noise ratio (SNR) and contrast noise ratio (CNR) of the image artifacts.The scanning time was recorded.Paired-t test and Mann-Whitney test were used respectively to compare the SNR and CNR,and qualitative scoring between the two sequences.P＜0.05 was considered to indicate a significant difference.Results The image distortion and blur of the WARP sequences were obviously reduced as compared to the conventional sequences.The SNR and CNR of artifacts of the WARP sequences were lower than that of the conventional sequences (All P＜0.05).The image quality scores of WARP sequences in cervical and lumbar spines[4(3 to 5) and 4(3 to 5)] were higher than that of conventional sequences[3(2 to 4),3(2 to 4)](P＜0.05).The scanning time of cervical spines in WARP sequence(14 min 9 s) was increased by 64 s (8.2％),and the time of lumbar spines (13 min 41 s) decreased by 9 s (1.1％).Conclusion The WARP sequences at 3.0 T could effectively reduce the artifacts of metallic prosthesis in cervical and lumbar spine without prolonging the scanning time at 3.0 T MRI.
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Computed tomography (CT) has been widely used in clinical diagnosis and made a great contribution to diagnosis by providing anatomical information with high-resolution.However,when metal implants exist in patients' body,reconstructed CT images are seriously interfered by metal artifacts.Metal artifacts are usually expressed as many dark and bright radiant streak artifacts which seriously reduce diagnosis reliability and bring errors into the calculation of dose distribution in radiotherapy.Therefore,the study of metal artifact reduction (MAR)is of great importance.This article reviews main methods on MAR developed in recent years,and give deep analysis on some of the methods.
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Objective To evaluate the value of gemstone spectral imaging (GSI)and multi artifact reduction system(MARs)in re-ducing metallic implants artifacts,and find the best monochromatic images.Methods Twenty-one patients with metal implants in our hospital receievd GSI examination ,MARS reconstruction and polychromatic images(140 kVp).Eleven groups of monochromatic and MARS images were obtained from 40 keV to 140 keV every interval of 10 keV by the special GSI viewer ,respetively.Subjective image quality of two methods were assessed by 3 radiologists in consensus.For every patient one group monochromatic images and blend enery images were selected two heaviest artifacts level and no artifacts level,the CT value and the standard deviations(SD)value of the region of interest(ROI)were meatured of artifacts.Contrast-to-noise ratio(CNR)and artifacts index(AI)were also caculated and were analyzed with paired-t test.Results There was significant statistical differences of CNR between energy spectral images and blend energy images in energy level of 40 to 120 keV(P 0.05),and the optimal CNR was acquired at the energy level of 70 keV(CNR=8.75±3.28).The value of AI for two mehtods has no difference in energy level scope 40 to 60 keV(P >0.05),there was significant statistical differences of AI between energy spectral images and blend energy images in energy level of 70 to 140 keV(P <0.05),and the lowest of AI(AI=26.95±9.64)was ac-quired at 1 10 keV images.Conclusion The energy spectral CT possess superiority in decreasing the artifacts and will provide high image quality in the metal implants.Gemstone spectral CT has great significance for postoperative patients with metal implants in imaging diagnosis.
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Objective To evaluate the value of digital tomosynthesis (TOMOS)in diagnosis of odontogenic cystic lesions of the jaws with oral fixed metal dentures, and compared with multi-slice spiral CT (MSCT). Methods The imaging findings of 40 cases with fixed metal dentures pathologically proved odontogenic cystic lesions of the jaws jn retrospective were retrospectively analyzed.All cases were performed by MSCT and TOMOS scanning,and 13 cases enhanced at the same time. The characteristics of the imaging findings in TOMOS and MSCT were compared. The diagnosis merits and disadvantages, especially their ability to detect the lesions and adjacent structures,were assessed. Results There were no significant difference (consistency check Kappa value>0.4) in evaluating the structure characteristics of the lesions, the relationgship between the lesions and cortex ,and the relationship between the lesions and surrounding organs. TOMOS is superior to MSCT in displaying apical change, the same in pure cystic and cystic-solid lesions interfered by artifacts.However, it is inferior to MSCT in detection of soft tissue invasion. Conclusion There is similar assessment value of TOMOS and MSCT in displaying odontogenic cystic lesions of the jaws. TOMOS can be chosen when the imaging findings of the lesions are interfered by metal artifacts.