Low-dose computed tomography with 4th-generation iterative reconstruction algorithm in assessment of oncologic patients

AIM To compare radiation dose and image quality of lowdose computed tomography(CT) protocol combined with hybrid-iterative reconstruction algorithm with standarddose CT examinations for follow-up of oncologic patients. METHODS Fifty-one patients with known malignant diseases which underwent, during clinical follow-up, both standarddose and low-dose whole-body CT scans were enrolled. Low-dose CT was performed on 256-row scanner, with 120 kV and automated m A modulation, and iterative reconstruction algorithm. Standard-dose CT was performed on 16-rows scanner, with 120 kV, 200-400 m As(depending on patient weight). We evaluated density values and signal-to-noise ratio, along with image noise(SD), sharpness and diagnostic quality with 4-point scale.RESULTS Density values in liver, spleen and aorta were higher in lowdose images(liver 112.55 HU vs 103.90 HU, P < 0.001), as SD values in liver and spleen(liver 16.81 vs 14.41). Volumetric-Computed-Tomographic-Dose-Index(CTDIvol) and Dose-Length-Product(DLP) were significantly lower in low-dose CT as compared to standard-dose(DLP 1025.6 m Gy*cm vs 1429.2 m Gy*cm, P < 0.001) with overall dose reduction of 28.9%. Qualitative analysis did not reveal significant differences in image noise and diagnostic quality.CONCLUSION Automatic tube-current modulation combined with hybriditerative algorithm allows radiation dose reduction of 28.9% without loss of diagnostic quality, being useful in reducing dose exposure in oncologic patients.

Quantitative evaluation of deep convolutional neural network-based image denoising for low-dose computed tomography

To minimize radiation risk,dose reduction is important in the diagnostic and therapeutic applications of computed tomography(CT).However,image noise degrades image quality owing to the reduced X-ray dose and a possible unacceptably reduced diagnostic performance.Deep learning approaches with convolutional neural networks(CNNs)have been proposed for natural image denoising;however,these approaches might introduce image blurring or loss of original gradients.The aim of this study was to compare the dose-dependent properties of a CNN-based denoising method for low-dose CT with those of other noise-reduction methods on unique CT noise-simulation images.To simulate a low-dose CT image,a Poisson noise distribution was introduced to normal-dose images while convoluting the CT unit-specific modulation transfer function.An abdominal CT of 100 images obtained from a public database was adopted,and simulated dose-reduction images were created from the original dose at equal 10-step dose-reduction intervals with a final dose of 1/100.These images were denoised using the denoising network structure of CNN(DnCNN)as the general CNN model and for transfer learning.To evaluate the image quality,image similarities determined by the structural similarity index(SSIM)and peak signal-to-noise ratio(PSNR)were calculated for the denoised images.Significantly better denoising,in terms of SSIM and PSNR,was achieved by the DnCNN than by other image denoising methods,especially at the ultra-low-dose levels used to generate the 10%and 5%dose-equivalent images.Moreover,the developed CNN model can eliminate noise and maintain image sharpness at these dose levels and improve SSIM by approximately 10%from that of the original method.In contrast,under small dose-reduction conditions,this model also led to excessive smoothing of the images.In quantitative evaluations,the CNN denoising method improved the low-dose CT and prevented over-smoothing by tailoring the CNN model.

Accuracy of baseline low-dose computed tomography lung cancer screening: a systematic review and meta-analysis

Background:Screening using low-dose computed tomography(LDCT)is a more effective approach and has the potential to detect lung cancer more accurately.We aimed to conduct a meta-analysis to estimate the accuracy of population-based screening studies primarily assessing baseline LDCT screening for lung cancer.Methods:MEDLINE,Excerpta Medica Database,and Web of Science were searched for articles published up to April 10,2022.According to the inclusion and exclusion criteria,the data of true positives,false-positives,false negatives,and true negatives in the screening test were extracted.Quality Assessment of Diagnostic Accuracy Studies-2 was used to evaluate the quality of the literature.A bivariate random effects model was used to estimate pooled sensitivity and specificity.The area under the curve(AUC)was calculated by using hierarchical summary receiver-operating characteristics analysis.Heterogeneity between studies was measured using the Higgins I 2 statistic,and publication bias was evaluated using a Deeks’funnel plot and linear regression test.Results:A total of 49 studies with 157,762 individuals were identified for the final qualitative synthesis;most of them were from Europe and America(38 studies),ten were from Asia,and one was from Oceania.The recruitment period was 1992 to 2018,and most of the subjects were 40 to 75 years old.The analysis showed that the AUC of lung cancer screening by LDCT was 0.98(95%CI:0.96-0.99),and the overall sensitivity and specificity were 0.97(95%CI:0.94-0.98)and 0.87(95%CI:0.82-0.91),respectively.The funnel plot and test results showed that there was no significant publication bias among the included studies.Conclusions:Baseline LDCT has high sensitivity and specificity as a screening technique for lung cancer.However,long-term follow-up of the whole study population(including those with a negative baseline screening result)should be performed to enhance the accuracy of LDCT screening.

Low-Dose High-Pitch Cardiac CT to Evaluate Abnormal Pacemaker Lead Position

Displacement of a cardiac pacemaker lead or myocardial perforation by a lead is an infrequent complication of pacemaker implantation. While standard cardiac CT is useful for diagnosing such complications when routine examinations can not, the potential risks associated with exposure to the high doses of radiation used in CT are of concern. Here, we report three cases in which pacemaker lead displacement or myocardial perforation was definitively diagnosed by low-dose cardiac CT used in the high-pitch spiral mode, when other more routine examinations failed to suggest their occurrence. The mean dose of radiation used for definitively diagnosing the three patients was relatively low (2.19 mSv).

Use of low-dose computed tomography to assess pulmonary tuberculosis among healthcare workers in a tuberculosis hospital

Background:According to the World Health Organization,China is one of 22 countries with serious tuberculosis(TB)infections and one of the 27 countries with serious multidrug-resistant TB strains.Despite the decline of tuberculosis in the overall population,healthcare workers(HCWs)are still at a high risk of infection.Compared with high-income countries,the TB prevalence among HCWs is higher in low-and middle-income countries.Low-dose computed tomography(LDCT)is becoming more popular due to its superior sensitivity and lower radiation dose.However,there have been no reports about active pulmonary tuberculosis(PTB)among HCWs as assessed with LDCT.The purposes of this study were to examine PTB statuses in HCWs in hospitals specializing in TB treatment and explore the significance of the application of LDCT to these workers.Methods:This study retrospectively analysed the physical examination data of healthcare workers in the Beijing Chest Hospital from September 2012 to December 2015.Low-dose lung CT examinations were performed in all cases.The comparisons between active and inactive PTB according to the CT findings were made using the Pearson chi-square test or the Fisher’s exact test.Comparisons between the incidences of active PTB in high-risk areas and non-high-risk areas were performed using the Pearson chi-square test.Analyses of active PTB were performed according to different ages,numbers of years on the job,and the risks of the working areas.Active PTB as diagnosed by the LDCT examinations alone was compared with the final comprehensive diagnoses,and the sensitivity and positive predictive value were calculated.Results:A total of 1012 participants were included in this study.During the 4-year period of medical examinations,active PTB was found in 19 cases,and inactive PTB was found in 109 cases.The prevalence of active PTB in the participants was 1.24%,0.67%,0.81%,and 0.53%for years 2012 to 2015.The corresponding incidences of active PTB among the tuberculosis hospital participants were 0.86%,0.41%,0.54%,and 0.26%.Most HCWs with active TB(78.9%,15/19)worked in the high-risk areas of the hospital.There was a significant difference in the incidences of active PTB between the HCWs who worked in the high-risk and non-high-risk areas(odds ratio[OR],14.415;95%confidence interval(CI):4.733-43.896).Comparisons of the CT signs between the active and inactive groups via chi-square tests revealed that the tree-in-bud,cavity,fibrous shadow,and calcification signs exhibited significant differences(P=0.000,0.021,0.001,and 0.024,respectively).Tree-in-bud and cavity opacities suggest active pulmonary tuberculosis,whereas fibrous shadow and calcification opacities are the main features of inactive pulmonary tuberculosis.Comparison with the final comprehensive diagnoses revealed that the sensitivity and positive predictive value of the diagnoses of active PTB based on LDCT alone were 100%and 86.4%,respectively.Conclusions:Healthcare workers in tuberculosis hospitals are a high-risk group for active PTB.Yearly LDCT examinations of such high-risk groups are feasible and necessary.

Evaluation with low-dose dual-phase helical computed tomography of patients with thyroid lesions

Background The incidence of thyroid cancer has been increasing.Our aim was to evaluate the efficacy of low-dose dualphase helical computed tomography （CT） in the characterization of thyroid lesions,and to discuss the relationship between image characteristics and their pathology.Methods One hundred and six patients with thyroid lesions underwent low-dose dual-phase helical CT after the injection of contrast material.CT scans were obtained at arterial and venous phase with delays of 25 and 65 seconds,and tube current of 60 and 120 mA,respectively.The attenuation change in the lesion between the arterial and venous phase was analyzed and categorized as ＂increased,＂ ＂decreased,＂ ＂mixed＂ or ＂no change.＂ Results Histopathologic diagnosis was obtained by surgery in 106 patients （115 lesions）.Of the 106 patients,45 had nodular goiter,5 thyroid adenoma,6 thyroiditis,and 50 papillary thyroid carcinoma （PTC） （59 lesions）.The attenuation value showed a significant difference （P ＜0.05） between the arterial and venous phase for the high attenuation area.There was statistical significant difference in terms of attenuation value in high attenuation areas at both phases and in low attenuation areas on arterial phase between nodular goiter and PTC （P ＜0.05）.However,there was no significant difference in attenuation value between adenoma and PTC.Twenty-nine cases （76.3％） of goiter manifested mixed type,3 cases （3/5） of adenoma showed decreased type,6 cases （6/6） of thyroiditis showed increased type,and 55 cases （93.2％） of PTC showed decreased type attenuation.The sensitivity,specificity for thyroid carcinoma by dual-phase CT were 94.9％ and 80.4％ respectively.The overall diagnostic accuracy for thyroid lesions by dual-phase CT was 87.8％.Conclusions The performance of dual-phase helical CT is related to the pathological structure of the lesions.The analysis of enhancement patterns by using dual-phase helical CT will be helpful in the differential diagnosis of thyroid lesions.

A NONLOCAL KRONECKER-BASIS-REPRESENTATION METHOD FOR LOW-DOSE CT SINOGRAM RECOVERY

Low-dose computed tomography(LDCT)contains the mixed noise of Poisson and Gaus-sian,which makes the image reconstruction a challenging task.In order to describe the statistical characteristics of the mixed noise,we adopt the sinogram preprocessing as a stan-dard maximum a posteriori(MAP).Based on the fact that the sinogram of LDCT has non-local self-similarity property,it exhibits low-rank characteristics.The conventional way of solving the low-rank problem is implemented in matrix forms,and ignores the correlations among similar patch groups.To avoid this issue,we make use of a nonlocal Kronecker-Basis-Representation(KBR)method to depict the low-rank problem.A new denoising model,which consists of the sinogram preprocessing for data fidelity and the nonlocal KBR term,is developed in this work.The proposed denoising model can better illustrate the generative mechanism of the mixed noise and the prior knowledge of the LDCT.Nu-merical results show that the proposed denoising model outperforms the state-of-the-art algorithms in terms of peak-signal-to-noise ratio(PSNR),feature similarity(FSIM),and normalized mean square error(NMSE).

LDCT筛查肺磨玻璃结节的影像学特征及临床诊疗进展

肺磨玻璃结节(GGO-nodules)是指在胸部CT上表现为磨玻璃样密度影的结节.随着CT扫描技术的不断发展与普及,GGO-nodules的检出率也越来越高.目前,这类结节的影像学诊断仍充满争议,探讨其系统化、标准化的诊断方法必将对于临床诊疗起到重要指导作用.本文综述了GGO-nodules最新的影像学及临床病理学研究进展,结合Fleischner学会(FS),美国国家综合癌症网(NCCN)及英国胸外科学会(BTS)的观点,探讨了GGO-nodules的诊治及随访原则,综述了微创组织活检及诊断标记物在肺磨玻璃结节中的作用,以及目前亚肺叶切除术在GGO-nodules治疗中的进展.

Assessment of the efficacy of reduced-radiation noncontrast computed tomography scan compared with the standard noncontrast computed tomography scan for detecting urolithiasis:A prospective single-center study

Background:Noncontrast computed tomography(CT)scan of the kidneys,ureter and bladder is the standard investigative modality for diagnosing and following up patients with urolithiasis.With each scan,a patient receives radiation of 18-34 mGy.Dose considerations become pertinent because of a 10%lifetime incidence rate and higher than 50%risk of recurrence,necessitating repeated imaging in the lifetime of a stone former.Hence,this study aimed to assess the sensitivity of"reduced-radiation"CT imaging by altering scan settings to lower than the"standard"norms.Materials and methods:Altogether,222 patients(255"kidney-ureter"stone-bearing units or"renal units")with urolithiasis and patients undergoing CT for other reasons with incidental findings of renal/ureteric calculi between 2017 and 2019 were included.All patients were subjected to 3 sequential scans at tube current settings of 250 mA(CT-N/Standard),100 mA(CT-100),and 50 mA(CT-50)at a constant voltage of 120 kV.Their clinicodemographic and radiological findings were recorded and assessed for significance.Results:Of the 255 renal units,117 were between 30 and 44 years of age,75%were men.Of the 255 patients,178(70.1%)reported a first stone episode and 77 had recurrence.Lower ureteric calculi were predominant(40.4%).All calculi were identified on CT-N;CT-100 failed to detect calculi in 1 patient,and CT-50 failed in 3 patients,where all calculi were<3 mm in size.Meanwhile,none were undetected among patients with obesity.The sensitivity was 99.61%for the CT-100 and 98.82%for the CT-50,which indicated a 2.5 and 5 times lower radiation and dose/length,respectively,than CT-N.Conclusions:The reduced-radiation CT scan is safe,sensitive,and accurate for the diagnosis and follow-up of patients with urolithiasis with significantly lower radiation exposures.Our study lays the foundation to accept low-dose CT in general and CT-50 in particular,as the new"standard of care,"and attempt further dose reduction without loss of diagnostic efficacy.

Cost-effectiveness of lung cancer screening by low-dose CT in China:a micro-simulation study

Background:The effectiveness of lung cancer screening with low-dose computed tomography(LDCT)has been established.The current study evaluates the cost-effectiveness of lung cancer screening with LDCT in a general population in China.Methods:A previously validated micro-simulation model was used to simulate a cohort of men and women on a lifetime horizon in the presence and absence of LDCT screening.The modeling data were collected from numerous national and international sources.Simulated screening scenarios included different combinations of screening intervals and start and stop ages.Additional costs(valued in Chinese Yuan,CNY;1 USD=6.8976 CNY,1 EUR=7.8755 CNY in 2020),life-years gained(LYG)and mortality reduction due to screening were also determined.The costs and life-years were discounted by 3%.All results were scaled to 1,000 individuals.The average cost-effectiveness ratio(ACER)was calculated.A willingness-to-pay threshold of CNY 217.3k/LYG was considered.A healthcare system perspective was adopted.Results:Compared to no screening,lung cancer screening by LDCT in a general Chinese population yielded 21.0-36.7 LYG in men and 9.2-16.6 LYG in women across the scenarios.For men,biennial LDCT screening yielded an ACER of CNY 171.4k-306.3k/LYG relative to no screening.Biennial screening performed between 55 and 75 years of age was optimal at the defined threshold;it resulted in CNY 174.6k/LYG and a lung cancer mortality reduction of 9.1%,and this scenario had a 75%probability of being cost-effective.For women,the ACER ranged from CNY 364.2k to 1193.3k/LYG.Conclusions:In China,lung cancer screening with LDCT in the general population including never smokers could be cost-effective for men with 75%probability,but not for women.The optimal strategy for men would be performing biennial screening between 55 and 75 years of age.

生成对抗网络下的低剂量CT图像增强

为去除低剂量计算机断层扫描(LDCT)图像中的噪声,增强去噪后图像的显示效果,提出一种生成对抗网络(GAN)下的LDCT图像增强算法。首先,将GAN与感知损失、结构损失相结合对LDCT图像进行去噪;然后,对去噪后的图像分别进行动态灰度增强和边缘轮廓增强;最后,利用非下采样轮廓波变换(NSCT)将增强后的图像在频域上分解为具有多方向性的系数子图,并将配对的高低频子图使用卷积神经网络(CNN)进行自适应融合,以重构得到增强后的计算机断层扫描(CT)图像。使用AAPM比赛公开的真实临床数据作为实验数据集,进行图像去噪、增强、融合实验,所提方法在峰值信噪比(PSNR)、结构相似度(SSIM)和均方根误差(RMSE)上的结果分别为33.015 5 dB、0.918 5和5.99。实验结果表明,所提算法在去除噪声的同时能保留CT图像的细节信息,提高图像的亮度和对比度,有助于医生更加准确地分析病情。

澳門地區吸煙人群中COPD和PRISm的現況及肺功能異常與肺癌的相關性研究

目的瞭解澳門地區吸煙人群中慢性阻塞性肺疾病(Chronic obstructive pulmonary disease,COPD)和PRISm(Preserved ratio impaired spirometry,PRISm)的現況及肺功能異常與肺癌的相關性。方法2017年5月~2019年12月,對吸煙人士進行胸部低劑量CT(Low dose computed tomography,LDCT)檢查和肺通氣功能檢查,分析PRISm、COPD檢出率,並按照肺通氣功能類型分為正常組、PRISm組,和COPD組,研究三組的不同特點及與肺癌的相關性。結果291例完成了檢查,發現PRISm 32例,檢出率11.0%(95%CI:7.4%~14.6%);COPD 98例,檢出率33.7%(95%CI:28.3%~39.3%)。共檢出肺癌10例。正常組、PRISm組、COPD組的肺癌檢出率分別為0.63%、12.5%、5.1%(X2值為15.79,P<0.00)。相對於肺功能正常組,PRISm組的肺癌危險度O R為20.13(95%CI:2.33~174.20)。肺功能異常組的肺癌危險度OR為11.08(95%CI:1.39~88.57)。LDCT和肺功能診斷COPD的一致性低(Kappa=0.24,P<0.05)。結論吸煙人群中COPD檢出率高;LDCT診斷COPD的正確指數低;PRISm和肺功能異常是肺癌的危險因素,建議在吸煙人群篩查肺癌的同時進行肺通氣功能檢查篩查COPD和PRISm。

低剂量螺旋CT对高危人群肺癌筛查价值的Meta分析

目的应用Meta分析法综合评价低剂量螺旋CT(low-dose spiral computed tomography,LDCT)在肺癌筛查中的价值。方法在PubMed、Cochrane等数据库检索1996年至2010年期间的相关文献资料;根据纳入标准筛选符合条件的文献;对文献进行信息统计、科学性评估及质量分级;采用随机效应模型进行数据分析;通过似然比(likelihoodratio,LR)、加权灵敏度和特异度(pooled sensitivity and specificity)及汇总受试者工作特征曲线(summary receiveroperator characteristic curve,SROC曲线)等统计指标综合评价LDCT在肺癌筛查中的价值。结果共纳入12篇英文文献,由9个独立研究构成,研究对象28 024例。文献质量评估结果提示纳入文献质量较好;LDCT在肺癌筛查中价值的合并阳性似然比(+LR)为3.35,阴性似然比(-LR)为0.29,加权灵敏度为0.735(0.730～0.740),特异度为0.791(0.747～0.830),SROC曲线下面积(area under curve,AUC)为0.847 3。结论多数独立研究单位报道的LDCT在早期肺癌筛查中的价值评价一致。通过汇总相关研究结果显示,LDCT在早期肺癌筛查中具有较高的价值,但仍需要高质量的随机对照研究以更准确地评价其临床价值。

自适应加权全变分的低剂量CT统计迭代算法

针对低剂量计算机断层扫描(LDCT)重建图像时出现条形伪影和脉冲噪声的现象,提出一种自适应加权全变分的LDCT统计迭代重建算法。该算法克服了传统全变分(TV)算法在去除条形伪影的同时引入阶梯效应的缺点,把基于加权方差的加权因子与TV模型相结合提出自适应加权全变分模型,然后再把新模型应用到惩罚加权最小二乘(PWLS)重建算法中,这样就可以对图像的不同区域进行不同强度的去噪,从而取得噪声抑制和边缘保持的良好效果。采用Shepp-Logan模型和数字骨盆体模来验证算法的有效性,实验结果表明,所提算法的归一化均方距离和归一化平均绝对距离均比滤波反投影(FBP)、PWLS、惩罚加权最小二乘的中值先验(PWLS-MP)以及惩罚加权最小二乘的全变分(PWLS-TV)算法的值小,且可分别获得40.91 dB和42.25 dB的峰值信噪比。实验结果表明,该算法重建出的图像在有效去除条形伪影的同时对图像的边缘和细节起到很好的保护作用。

低剂量螺旋CT肺癌筛查的临床价值

肺癌作为我国第一大癌种,其早期诊断越来越受到临床工作者的重视。20世纪90年代以前,对肺癌的筛查主要依靠痰细胞学或胸部X线检查。但这些筛查方法并没有使肺癌的死亡率有显著的降低。1990年之后,一批以低剂量螺旋CT作为肺癌筛查手段的临床试验开始崛起。人们发现相比胸部X线检查,低剂量螺旋CT能筛查出更多、直径更小的早期肺癌。本文主要针对低剂量螺旋CT作为肺癌筛查手段的历史和现状加以阐述,探索低剂量螺旋CT的临床价值及应用前景。

人工智能联合低剂量肺部CT扫描在肺原位癌筛查中的诊断价值

目的:研究人工智能(AI)辅助诊断系统联合低剂量肺部CT扫描在肺原位癌筛查中的应用价值。方法:选取医院行低剂量CT(LDCT)发现肺部结节的100例患者(130个结节)进行AI联合LDCT诊断,将胸腔镜病理结果为早期肺癌诊断“金标准”,比较AI联合LDCT诊断与单纯LDCT诊断肺癌的差异,分析对肺原位癌诊断灵敏度、特异度和准确率的诊断效能。结果:AI联合LDCT对于直径≤5 mm结节、完全实性结节、磨玻璃结节、胸膜下结节以及外周型和中心型结节的早期肺癌检出率显著高于LDCT诊断,差异有统计学意义(χ^(2)=30.355,χ^(2)=9.426,χ^(2)=23.587,χ^(2)=9.553,χ^(2)=16.321,χ^(2)=6.335;P<0.05)。130个肺部结节中确诊恶性结节55个,良性结节75个。LDCT检出恶性结节82个(其中32个结节病理最后确诊为良性),良性结节48个;AI联合LDCT检出恶性结节53个,良性结节77个。AI联合LDCT对早期肺癌的诊断灵敏度、特异度、阳性预测值、阴性预测值和准确率分别为94.55%、98.67%、98.11%、96.10%和96.92%,LDCT诊断的特异度、阳性预测值和准确率分别为57.33%、64.10%和71.54%,显著低于AI联合LDCT诊断,差异有统计学意义(χ^(2)=37.335,χ^(2)=21.177,χ^(2)=33.393;P<0.05)。但两种检查方法的诊断灵敏度和阴性预测值之间无明显差异。结论:AI联合LDCT对于早期肺癌的诊断效率更高,可作为临床医师筛查肺结节的有效手段,具有一定的临床诊断意义。

平稳小波域深度残差CNN用于低剂量CT图像估计

针对低剂量计算机断层扫描(LDCT)重建图像中存在大量噪声的问题,提出了一种平稳小波的深度残差卷积神经网络(SWT-CNN)模型,可以从LDCT图像估计标准剂量计算机断层扫描(NDCT)图像。该模型在训练阶段,将LDCT图像经平稳小波(SWT)三级分解后的高频系数作为输入,将LDCT图像高频系数与NDCT图像高频系数相减得到残差系数作为标签,通过深度卷积神经网络(CNN)学习输入和标签之间的映射关系;在测试阶段,利用此映射关系即可从LDCT图像的高频系数中预测NDCT高频系数,最后通过平稳小波反变换(ISWT)重构预测的NDCT图像。实验采用50对大小为512×512的同一体模的常规剂量胸腔及腹腔扫描切片和投影域添加噪声后的重建图像作为数据集,其中45对作为训练集,其余5对作为测试集。将所提模型与效果较好的非局部降噪算法、K-奇异值分解(K-SVD)算法、匹配三维滤波(BM3D)算法及图像域CNN(Image-CNN)模型对比,实验结果表明,SWT-CNN模型预测的NDCT图像信噪比(PSNR)和结构相似性(SSIM)高,且均方根误差(RMSE)小于其他算法处理结果。该模型对于提高低剂量CT图像质量是可行且有效的。

基于VGG网络与深层字典的低剂量CT图像去噪算法

低剂量计算机断层扫描(LDCT)能够有效降低X射线辐射对人体健康造成的危害,已广泛应用于医学临床诊断。针对LDCT图像中存在大量的斑点噪声和条形伪影的问题,提出一种结合改进的VGG网络和深层字典的图像去噪算法,以弥补深层字典去噪能力的不足。在深层字典学习到第一层字典原子和稀疏矩阵后,通过改进的VGG网络将字典原子区分为信息原子和噪声原子,同时将稀疏矩阵中噪声原子所对应的元素设置为零,降低噪声原子对图像去噪效果的影响。实验结果表明,与K-SVD算法、正则化K-SVD算法和深层字典学习算法相比,该算法的峰值信噪比和结构相似性指数平均提高了1.4 dB和0.03,能够有效抑制LDCT图像噪声和伪影,且保留较多的边缘和细节信息。

用于低剂量CT降噪的伪影感知生成对抗网络

近年来,生成对抗网络(GAN)用于低剂量CT(LDCT)伪影抑制表现出一定性能优势,已成为该领域新的研究热点。由于伪影分布不规律且与正常组织位置息息相关,现有GAN网络的降噪性能受限。针对上述问题,提出了一种基于伪影感知GAN的LDCT降噪算法。首先,设计了伪影方向感知生成器,该生成器在U型残差编解码结构的基础上增加了伪影方向感知子模块(ADSS),从而提高生成器对伪影方向特征的敏感度;其次,设计了注意力判别器(AttD)来提高对噪声伪影的鉴别能力;最后,设计了与网络功能相对应的损失函数,通过多种损失函数协同作用来提高网络的降噪性能。实验结果表明,与高频敏感GAN(HFSGAN)相比,该降噪算法的平均峰值信噪比(PSNR)和结构相似度(SSIM)分别提升了4.9%和2.8%,伪影抑制效果良好。

单体检中心23695例体检者首次胸部低剂量CT筛查结果及肺结节相关易感因素的研究

目的通过对体检者胸部低剂量CT(low-dose computed tomography,LDCT)筛查的结果及肺结节的相关易感因素进行分析,为早期肺癌筛查提供科学依据。方法回顾性搜集体检中心23695例体检者首次进行LDCT筛查的资料,对疑似肺癌的随访结果以及相关年龄、性别、生活史、既往史、家族史及部分检查状况进行整理统计。结果本次筛查肺结节检出率79.79%,其中实性结节为71.43%,亚实性结节为22.98%;其他方面以心血管和肝脏疾病的检出率较高,分别为21.42%和24.49%。另外,疑似肺癌病例315例,随访确诊肺癌84例,其中Ⅰ期占比最高(69.05%,58例)、其次是Ⅱ期(20.24%,17例),早期诊断率为89.29%。肺结节的恶性病变检出率为0.44%,肺癌检出率为0.35%。其中部分实性结节的恶性病变率及确诊肺癌检出率较实性结节偏高。性别、年龄、吸烟、高血压病史是肺结节发生的独立易感因素(OR=0.969、0.790、0.922、0.863,均P<0.05)。结论LDCT适合对人群进行大规模肺癌筛查,有助于及早发现肺内及其他部位可疑病变。在临床筛查过程中,更应重视对男性、年龄≥55岁、有吸烟史及高血压史等易感人群的肺癌筛查。