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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
@#Introduction: Metal artifacts can degrade the image quality of computed tomography (CT) images which lead to errors in diagnosis. This study aims to evaluate the performance of Laplace interpolation (LI) method for metal artifacts reduction (MAR) in CT images in comparison with cubic spline (CS) interpolation. Methods: In this study, the proposed MAR algorithm was developed using MATLAB platform. Firstly, the virtual sinogram was acquired from CT image using Radon transform function. Then, dual-adaptive thresholding detected and segmented the metal part within the CT sinogram. Performance of the two interpolation methods to replace the missing part of segmented sinogram were evaluated. The interpolated sinogram was reconstructed, prior to image fusion to obtain the final corrected image. The qualitative and quantitative evaluations were performed on the corrected CT images (both phantom and clinical images) to evaluate the effectiveness of the proposed MAR technique. Results: From the findings, LI method had successfully replaced the missing data on both simple and complex thresholded sinogram as compared to CS method (p-value = 0.17). The artifact index was significantly reduced by LI method (p-value = 0.02). For qualitative analysis, the mean scores by radiologists for LI-corrected images were higher than original image and CS-corrected images. Conclusion: In conclusion, LI method for MAR produced better results as compared to CS interpolation method, as it worked more effective by successfully interpolated all the missing data within sinogram in most of the CT images.
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Background: Thorax MSCT examination is a diagnostic imaging that is capable of displaying both normal and pathological lung and respiratory organs. MSCT examination also has a better level of sensitivity and specificity compared to other modalities, but the radiation exposure given is very high, so the radiation dose given to patients is high. The reduction in radiation dose is very important because of the direct exposure to sensitive tissue. One method of reducing radiation dose is by reducing the tube voltage. However, the decrease in tube voltage causes a decrease in image quality as indicated by increased noise and decreased CNR. To maintain the quality of the image at low tube voltage setting, an IR reconstruction of SAFIRE was used. The purpose of this research is to know the impact of using SAFIRE on dose radiation and image quality of thorax MSCT.Methods: This study was an experimental study with a quasi-experimental study design. The object used was the N-1 Lungman chest phantom in which an artificial tumor was attached. Radiation dose assessment used CTDI value, while image quality assessment used noise and CNR. Data processing was conducted using linear regression test.Results: There was an effect of tube voltage setting and SAFIRE setting on radiation dose and image quality.Conclusions: Tube voltage ssetting and SAFIRE setting had an effect on radiation dose and image quality. Tube voltage setting and SAFIRE strength level setting that were able to provide optimal radiation dose and image quality were tube voltage of 80 kVp and SAFIRE strength levels 3 and 4 (S3 and S4).
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Objective ToevaluateimagequalityoflowerextremityCTAoflowradiationdoseandlowcontrastmediumprotocol withsinogram-affirmediterativereconstruction(SAFIRE).Methods Thisstudyincluded116patientswhoreferredtolowerextremityCT angiographyusinga128-sliceCTscanner.Accordingtovoltageandcontrastmediumconcentration,patientsweredividedintofour groups:100kV+350mgI/mL,100kV+320mgI/mL,100kV+300mgI/mL,80kV+CarekV+300mgI/mL.Imagereconstructionunderwent conventionalfilteredback-projection (FBP)andSAFIREtechniqueineachprotocoltocompareSNR,CNRofarterialimages.Results Comparisonoftwosubgroupsinthesamegroup,SAFIREhadsignificantlyhigherimagequalitythanFBP.Comparisonamong groupsshowed:imagequalityinlowcontrastmediumandlowradiationdoseSAFIREgroupcouldreachsimilarorbetterthanthatin higherdoseFBPgroup.SAFIREcouldreduceimagenoiseandimproveimageSNRandCNR.Conclusion InlowerextremityCTA, 80kV+CarekV,300mgI/mLcontrastmediumwithSAFIREexamineprotocolcouldreducecontrastmediumconcentrationandradiationdose withnocompromiseddiagnosticdemand.
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The accurate position of the center of rotation (COR) is a key factor to ensure the quality of computed tomography (CT) reconstructed images. The classic cross-correlation matching algorithm can not satisfy the requirements of high-quality CT imaging when the projection angle is 0 and 180°, and thus needs to be improved and innovated. In this study, considering the symmetric characteristic of the 0° and flipped 180° projection data in sinogram, a novel COR correction algorithm based on the translation and match of the 0° and 180° projection data was proposed. The OTSU method was applied to reduce noise on the background, and the minimum offset of COR was quantified using the -norm, and then a precise COR was obtained for the image correction and reconstruction. The Sheep-Logan simulation model with random gradients and Gaussian noise and the real male SD rats samples which contained the heterogenous tooth image and the homogenous liver image, were adopted to verify the performance of the new algorithm and the cross-correlation matching algorithm. The results show that the proposed algorithm has better robustness and higher accuracy of the correction (when the sampled data is from 10% to 50% of the full projection data, the COR value can still be measured accurately using the proposed algorithm) with less computational burden compared with the cross-correlation matching algorithm, and it is able to significantly improve the quality of the reconstructed images.
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Objective To assess the image quality (IQ) of an iterative reconstruction (IR) technique(sinogram affirmed iterative reconstruction,SAFIRE) for upper limb intravascular fistula CT angiography on a second generation dual-source CT scanner and determine the optimal dose level using IR with IQ comparable to filtered back projection(FBP).Methods The experiment was a prospective study.A total of 150 patients were averagely divided into 5 groups to perform upper limb intravascular fistula CT angiography.The control group was scanned with conventional tube output (120 kV,110 mAs) and images were reconstructed with FBP.The tube current of the other 4 groups (reconstructed with SAFIRE) was successively reduced to 70％,60％,50％ and 40％ of that of control group.Quantitative measurements of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were obtained in two regions of interest (ROI) in each group.The ROIs were placed at the subclavian artery near shoulder joint,and the stoma of radial artery and cephalic vein.Analysis of variance (ANOVA) was used for comparisons of objective evaluation parameters (SNR,CNR) and radiation dose (CTDIvol,DLP,E) among 5 groups.Two radiologists graded IQ in a blinded fashion on a 4-point scale (4-excellent,3-good,2-fair and 1-poor).The Kruskal-Wallis nonparametric test was performed for detection of differences in subjective evaluation of IQ among groups.Results The radiation doses of groups 77,66,55 and 44 mAs were 70％,55％,40％ and 25％ of the control group respectively.The differences of SNR and CNR among groups 77,66,44 mAs and the control group were statistically significant in ROI1 (F =24.018,20.386,P ＜ 0.05),SNR and CNR of group 77 and 66 mAs were higher than the control group while group 44 mAs was lower.The difference of SNR and CNR among group 55 mAs and the control group was not statistically significant in ROI1 (P ＞ 0.05).The differences of SNR and CNR among groups 77,66,55 mAs and the control group were statistically significant in ROI2 (F =15.934,13.818,P ＜ 0.05),and groups 77,66 and 55 mAs had higher SNR and CNR.The difference of SNR and CNR between group 44 mAs and the control group was not statistically significant in ROI2 (P ＞ 0.05).Groups 77,66,55 mAs and the control group had higher scores of the subjective IQ (≥ 3) which was descended in group 44 mAs.The differences of contrast,sharpness,noise and general impression of images among the 5 groups were statistically significant by Kruskal-Wallis nonparametric test(H =10.268,14.542,15.840,11.014,P ＜ 0.05).Using the criterion of excellent IQ(score 4),the ROC curve of dose levels and IQ acceptability established a reduction of 60％ of effective dose [Group 55 mAs:(3.545 ± 1.396) mSv] as an optimum cutoff point (AUC:0.844,95％ CI:0.705-0.982).Conclusions Iterative reconstruction technique could provide a dose reduction to 40％ (3.545 mSv) compared with the filtered back projection in upper limb intravascular fistula CT angiography without reducing equivalent image quality.
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Objective To evaluate the image quality,diagnosis accuracy and dose reduction of split-bolus CT urography (CTU) with low voltage scan and sinogram affirmed iterative reconstruction (SAFIRE).Methods A total of 80 cases of consecutive patients with confirmed or suspected urinary system disease needed CTU examination were divided into two groups (control group and test group) by using random number table.In control group,convention scan (120 kV) with one time injection was used.But low voltage scan (80 kV) with SAFIRE algorithm and split-bolus injection (SBI) was used in experiment group.The radiation dose,image quality and diagnosis accuracy were compared.Results A total of 77 cases completed CTU examination successfully in the two groups,including 39 cases in control group and 38 cases in test group.The effective dose reduced from (26.68 ± 4.07) in control group to (3.93 ± 0.85) mSv in test group (t =-33.78,P ＜ 0.05).Subjective image quality score was (4.49 ± 0.79) in control group and (4.39 ± 1.53) in test group,with no significantly statistical difference (Z =2.71,P ＞ 0.05).Signal-to-noise ratio (SNR) of objective image quality in test group was higher than that in control group (127.3±15.9 vs.109.6 ± 13.2,t =4.49,P＜0.05).But there was no significantly statistical difference in contrast-to-noise ratio (CNR) between control group(100.8 ± 12.9)and test group (109.0 ± 14.4,P ＞ 0.05).For diagnosis accuracy,no statistical difference were found between two groups(84.62％ and 81.58％,P ＞ 0.05).Conclusions The combination of low voltage scan with SAFIRE algorithm and split-bolus injection CTU could reduce the radiation dose significantly,but the objective image quality,CNR (except SNR) of subjective image quality and diagnosis accuracy were all unaffected obviously.
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OBJECTIVE: To assess the lesion conspicuity and image quality in CT evaluation of small (< or = 3 cm) hepatocellular carcinomas (HCCs) using automatic tube voltage selection (ATVS) and automatic tube current modulation (ATCM) with or without iterative reconstruction. MATERIALS AND METHODS: One hundred and five patients with 123 HCC lesions were included. Fifty-seven patients were scanned using both ATVS and ATCM and images were reconstructed using either filtered back-projection (FBP) (group A1) or sinogram-affirmed iterative reconstruction (SAFIRE) (group A2). Forty-eight patients were imaged using only ATCM, with a fixed tube potential of 120 kVp and FBP reconstruction (group B). Quantitative parameters (image noise in Hounsfield unit and contrast-to-noise ratio of the aorta, the liver, and the hepatic tumors) and qualitative visual parameters (image noise, overall image quality, and lesion conspicuity as graded on a 5-point scale) were compared among the groups. RESULTS: Group A2 scanned with the automatically chosen 80 kVp and 100 kVp tube voltages ranked the best in lesion conspicuity and subjective and objective image quality (p values ranging from < 0.001 to 0.004) among the three groups, except for overall image quality between group A2 and group B (p = 0.022). Group A1 showed higher image noise (p = 0.005) but similar lesion conspicuity and overall image quality as compared with group B. The radiation dose in group A was 19% lower than that in group B (p = 0.022). CONCLUSION: CT scanning with combined use of ATVS and ATCM and image reconstruction with SAFIRE algorithm provides higher lesion conspicuity and better image quality for evaluating small hepatic HCCs with radiation dose reduction.
Subject(s)
Adult , Aged , Aged, 80 and over , Female , Humans , Male , Middle Aged , Young Adult , Algorithms , Carcinoma, Hepatocellular/diagnostic imaging , Contrast Media , Fluoroscopy , Image Enhancement/methods , Liver Neoplasms/diagnostic imaging , Prospective Studies , Radiation Dosage , Radiographic Image Interpretation, Computer-Assisted/methods , Tomography, X-Ray Computed/methodsABSTRACT
Objective To explore the optimized scanning parameters of low-dose un-enhanced chest CT with sinogram affirmed iterative reconstruction (SAFIRE).Methods Eleven healthy adult domestic dogs underwent chest scanning of 120 kV,100 kV,80 kV,70 kV with a fixed tube current of 65 mA and halved tube current of 32 mA with a fixed tube voltage of 100 kV.The data were reconstructed with filtered back projection (FBP)and SAFIRE (strength grade 3)respectively to obtain ten groups of images.The regular dose (120 kV/65 mA ) combining with FBP reconstruction was as normal control group,and other groups as experimental groups.CT dose index (CTDI), dose length product (DLP),and effective dose (ED)at different dose were compared,and average CT value,noise,signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR)and image quality score of ten groups of images were comparatively analyzed.Results No significant differences were found in average CT value for lung tissue,the superior vena cava,the aortic arch,and spinal muscles among ten groups (P >0.05),except adipose tissue (P 3),and the radiation dose of this group decreased by 81.33%.Conclusion Reconstructed with SAFRIE technology,the image quality of 100 kV/65 mA scanning of chest CT is similar to that of routinely reconstructed images in regular dose,while the image quality of 70 kV/65 mA scanning can not only meet the requirements of diagnosis but also obviously reduce radiation dose.
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Objective To evaluate the value of the SAFIRE reconstruction technique for the nasal traumatic lesions .Methods Six‐ty‐seven patients with nasal traumas were scanned by the orbital scan and were reconstructed with FBP and SAFIRE (strength grade 1 to 5) respectively .Then a comparative analysis for six kinds of reconstructed images were conducted on the average CT value ,noise ,signal to noise ratio (SNR) ,contrast to noise ratio (CNR) ,subjective scoring and lesion detection .Results Compared with reconstruction by FBP , SAFIRE (strength grade 1 to 5)reconstruction ,for the noise ,decreased to 20 .4% ,31 .4% ,39 .7% ,46 .5% and 57 .2% respectively ;For the SNR ,increased to 33 .3% ,54 .7% ,75 .4% ,87 .4% and 101 .4% respectively ;For the CNR ,it also increased to 23 .0% ,36 .4% ,57 .7% , 87 .4% and 106 .5% respectively ;The difference was statistically significant (P< 0 .05) .For the images of SAFIRE‐1 and SAFIRE‐5 ,the image subjective scoring was lower than that by FBP ;for the images of SAFIRE‐2 and SAFIRE‐4 ,the image subjective scoring was higher than that by FBP ;and SAFIRE‐3 had the highest score .But for the rate of lesion detection ,all the images were the same .Conclusion CT scan combined SAFIRE reconstruction technique can decrease effectively the noise and increase the image quality in the traumatic nasal scan , as well as has a potential effect to decrease the scan dose .
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Objective To investigate the value of low tube voltage with sinogram affirmed iterative reconstruction (SAFIRE) through comparing the image quality of regular dose scanning with filtered back projection (FBP) reconstruction and low-dose scanning with SAFIRE. Methods Eleven healthy adult domestic dogs were scanned with different doses. The regular dose of 120 kV/65 mA in combination with FBP reconstruction was set as the normal control group, and 100 kV/65 mA plus SAFIRE reconstruction was used as the low kV group. The CT dose index (CTDI), dose length product (DLP), and the effective dose (ED) at different doses were compared, and the average CT value, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and the image quality score of two groups of images were also analyzed. Results ED in the low kV groups was reduced by 39.33%compared to that in the normal control group. No significant differences were found in the average CT value of the same tissue among these two groups (P > 0.05). Compared with the normal control group, image noise of the lung tissue, superior vena cava and spinal muscle of low kV group were consistently decreased, SNR was in also creased, while the noise ratio contrast between superior vena cava and fat was increased. The image quality score of the low kV group was increased by 1.70%compared to that of the normal control group. Conclusion The low kV scan with SAFIRE technology can decrease the radiation dose and improve image quality in chest CT examination of domestic dogs, with a potential value in the clinical promotion and the application.
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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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PURPOSE: To establish the methods for sinogram formation and correction in order to appropriately apply the filtered backprojection (FBP) reconstruction algorithm to the data acquired using PET scanner with multiple scintillation crystal layers. MATERIAL AND METHODS: Formation for raw PET data storage and conversion methods from listmode data to histogram and sinogram were optimized. To solve the various problems occurred while the raw histogram was converted into sinogram, optimal sampling strategy and sampling efficiency correction method were investigated. Gap compensation methods that is unique in this system were also investigated. All the sinogram data were reconstructed using 2D filtered backprojection algorithm and compared to estimate the improvements by the correction algorithms. RESULTS: Optimal radial sampling interval and number of angular samples in terms of the sampling theorem and sampling efficiency correction algorithm were pitch/2 and 120, respectively. By applying the sampling efficiency correction and gap compensation, artifacts and background noise on the reconstructed image could be reduced. CONCLUSION: Conversion method from the histogram to sinogram was investigated for the FBP reconstruction of data acquired using multiple scintillation crystal layers. This method will be useful for the fast 2D reconstruction of multiple crystal layer PET data.