迭代重建算法的发展及其在CT中的应用

随着CT成像技术的不断发展,其在临床中的应用越来越广泛,而临床对于CT诊断的要求也不断提高。一直以来,CT检查的辐射剂量及图像质量的改善都是人们关注的热点。早期,降低辐射剂量的主要方法就是降低管电压、降低管电流、增加螺距及减少扫描次数等,但这些方法在降低辐射剂量的同时也在一定程度上降低了图像质量。随着CT技术的不断改进,不同类型的重建算法及扫描方式也随之出现,能够通过不同的重建算法来改善图像质量,从而有助于     

双源CT低剂量冠状动脉血管成像检查在临床中应用

近几年来,随着冠状动脉CT血管成像（CCTA）技术的不断提升,在临床中对于冠心病的诊断价值已得到认可与肯定［1］,但伴随着冠状动脉CT检查的高辐射剂量问题影响CCTA在临床发展。因此遵循ALARA（as low as reasonably achievable）原则控制辐射剂量在实际工作中越来越受到重视。作者就综合运用CCTA低剂量扫描方法在临床工作中作了初步总结,以评价低剂量扫描方法对于图像质量与辐射剂量的影响。报道如下。     

应用CT轴位扫描降低腰椎间盘病变放射辐射剂量的研究

目的探讨CT轴位扫描应用于腰椎间盘扫描以降低辐射剂量的可行性及其临床应用价值。方法随机抽取正常BMI的60例志愿者行CT腰椎间盘检查,在其他参数均相同情况下分别进行常规剂量(270 mA)和低剂量(180 mA、135 mA)扫描,比较两种不同低剂量CT扫描所得图像与常规剂量的图像质量差异,以及发现椎间盘病变的差异。结果在扫描图像质量方面,两种不同低剂量与常规剂量扫描有统计学差异(P<0.05)。但在诊断疾病方面,两种不同低剂量扫描与常规剂量扫描无统计学差异(P>0.05)。在满足诊断需要的同时,患者接受的辐射剂量分别降低36.5%及54.0%。结论轴位扫描应用于腰椎间盘CT扫描具有一定的可行性,并可大幅度降低患者辐射剂量。     

对比不同CT扫描方式的辐射剂量与图像质量

目的:对比评价常规CT扫描与胸部能谱成像应用于临床检查时的射线辐射剂量与图像质量。方法:将医院2017年1月~4月收治因病情需要行胸部CT检查的52例患者作为研究对象,患者均行常规CT平扫与胸部能谱成像扫描,并对两种CT扫描方式的辐射剂量与图像质量进行比较,以评价最佳扫描方式。结果:不同CT扫描方式比较可见,常规CT平扫与能谱动脉期成像的辐射剂量及图像质量相当(P0.05);而能谱静脉期成像虽然比常规CT平扫有较高辐射剂量,但所提供的图像质量也更佳(P0.05)。结论:与120k Vp常规CT平扫相比,胸部动脉期能谱成像的辐射剂相当,胸部静脉期能谱成像虽然有较高辐射剂量,但所获得的图像质量,可在临床酌情考虑应用。     

RevolutionCT对冠脉CTA图像质量的影响因素研究

越来越多的冠心病患者将冠脉CTA作为首选检查,而RevolutionCT作为超高端CT,在图像质量和辐射剂量之间取得了更好的平衡,在检查过程中,有诸多因素影响着图像质量及辐射剂量。     

体型特异性剂量估计的最新概念及临床应用

CT检查时设置扫描参数的原则是在得到临床诊断可接受的图像质量的前提下,尽可能降低辐射剂量。而患者所接受的辐射剂量,不仅与CT设备的输出剂量有关,也与患者本身体型相关。现有的CT设备提供的辐射剂量信息,如容积CT剂量指数（CTDI_vol）,是基于固定大小聚甲基丙烯酸甲酯模型测量所得,并未考虑到患者的不同体型信息。美国医学物理师学会（AAPM）在204和220报告中提出了一种新的患者辐射剂量估算方法——体型特异性剂量估计（SSDE）,综合考虑了CT辐射输出量和患者体型信息,能准确评估患者辐射剂量。本文对SSDE的最新概念和临床应用进展进行综述。     

冠状动脉CT血管造影成像中前瞻性与回顾性心电门控技术的比较

目的 评价前瞻性与回顾性心电门控冠状动脉CT血管造影成像的图像质量及辐射剂量.方法 选择心率≤65次/分,节律规则的冠状动脉受检者69例,随机分为实验组(34例)和对照组(35例),分别采用前瞻性和回顾性心电门控进行CT冠状动脉检查.记录两组的辐射剂量并进行统计学分析,同时采用双盲法对图像质量进行评价.结果 实验组和对照组的平均辐射剂量分别为(2.00±0.23)mSv、(10.20±0.96)mSv,差异有统计学意义(P＜0.001).两组各段冠状动脉图像质量方面差异无统计学意义(P＞0.05).结论 冠状动脉CT血管造影成像的前瞻性心电门控技术可大幅降低冠状动脉成像时的辐射剂量,对于心率较低的受检者具有推广价值.     

Flash双源CT低剂量扫描在冠脉成像中的应用

目的：比较双源FLASH CT不同扫描方案在冠脉成像中图像质量和辐射剂量的差别.材料与方法：对需做冠脉CT心率小于等于65次/分,心律整齐患者118例,随机分为A、B两组,分别采用Flash模式与前瞻性心电门控触发模式进行冠脉扫描,盲法评价分析A、B两组患者冠脉图像质量及X线辐射剂量.结果：Flash扫描模式下扫描与前门控触发扫描所得具有诊断价值的血管节段数和平均图像质量评分无显著统计学差异.Flash模式下扫描辐射剂量显著低于前瞻性心电门控触发模式.结论：Flash扫描模式能显著降低患者冠脉CTA的辐射剂量.     

双层光谱探测器CT临床应用与研究进展

双层光谱探测器CT从探测器角度进行技术革新，实现同时、同源、同向和同步能量分离扫描，可降低噪声、优化图像质量，提高病灶检出率，抑制伪影，具有定量定性分析物质、降低辐射剂量和减少对比剂用量等优势，临床应用前景广阔。本文对双层光谱探测器CT临床应用与研究进展进行综述。     

低剂量胸部CT扫描诊断肺癌的临床价值分析

目的探讨低剂量胸部CT扫描诊断肺癌的临床价值。方法选取就诊的64例肺癌患者为研究对象,分别进行常规剂量和低剂量胸部CT扫描。比较两种检查方式肺癌检出情况、图像质量及放射剂量等情况。结果常规剂量共检出肺癌63例,检出率为98.44%,低剂量共检出肺癌61例,检出率为95.31%。两组比较,差异无统计学意义(P0.05);常规剂量图像优良率为96.88%,低剂量图像优良率为93.75%,两组比较,差异无统计学意义(P0.05);低剂量中CT剂量容积及剂量长度乘积、CT权重剂量指数、最大有效辐射剂量均低于常规剂量,差异有统计学意义(P0.05)。结论低剂量胸部CT扫描应用于肺癌的临床诊断中,在降低辐射度的同时,具有较高的临床诊断准确率和图像质量,利于确保生命安全,值得推广。     

Feasibility of Using Iterative Reconstruction to Reduce Radiation Dose for Computed Tomography Pulmonary Angiograms

ObjectiveThe purpose of this study was to assess the potential for iterative reconstruction algorithms to be used to reduce patient radiation dose for computed tomography pulmonary angiography examinations while maintaining diagnostic image quality.Materials and MethodsThis two-stage study first considered current computed tomography pulmonary angiography image quality through an audit of current practice. Secondly, an experimental design was adopted using an anthropomorphic phantom with the addition of contrast-enhanced tubes to mimic pulmonary arteries. The radiation dose was reduced by incrementally reducing the milliampere seconds value from the standard institutional protocol, and subjective and objective (contrast-to-noise ratio [CNR] and signal-to-noise ratio [SNR]) quality measures were recorded for each exposure and reconstruction.ResultsA sample of 10 patients met the inclusion criteria for the audit, and a mean CNR of 44.2 and an SNR of 47.9 were established as baseline quality. A clear positive correlation was identified between the number of iterations and objective quality measures (CNR [r = 0.78, P < .001] and SNR [r = 0.78, P < .001]). No relationship was identified between the subjective measures and either radiation exposure (milliampere seconds) or the number of iterations. Findings suggest that a potential reduction in effective dose of 1.46 mSv (57.0%) is possible with no associated loss of image quality with the use of iterative reconstruction.ConclusionFindings suggest that the potential dose reduction may be as great as 57%; however, further work is required to confirm this in a patient population.     

Assessment of Image Quality and Dosimetric Performance of CT Simulators

BackgroundCT simulator for radiation therapy aims to produce high-quality images for dose calculation and delineation of target and organs at risk in the process of treatment planning. Selection of CT imaging protocols that achieve a desired image quality while minimizing patient dose depends on technical CT parameters and their relationship with image quality and radiation dose. For similar imaging protocols using comparable technical CT parameters, there are also variations in image quality metrics between different CT simulator models. Understanding the relationship and variation is important for selecting appropriate imaging protocol and standardizing QC process. Here, we proposed an automated method to determine the relationship between image quality and radiation dose for various CT technical parameters.Material and MethodThe impact of scan parameters on various aspects of image quality and volumetric CT dose index for a Philips Brilliance Big Bore and a Toshiba Aquilion One CT scanners were determined by using commercial phantom and automated image quality analysis software and cylindrical radiation dose phantom.Results and DiscussionBoth scanners had very similar and satisfactory performance based on the diagnostic acceptance criteria recommended by ACR, International Atomic Energy Agency, and American Association of Physicists in Medicine. However, our results showed a compromise between different image quality components such as low-contrast and spatial resolution with the change of scanning parameters and revealed variations between the two scanners on their image quality performance. Measurement using a generic phantom and analysis by automated software was unbiased and efficient.ConclusionThis method provides information that can be used as a baseline for CT scanner image quality and dosimetric QC for different CT scanner models in a given institution or across sites.     

乳腺摄影自动曝光模式控制下DR系统、PCM系统和CR系统的比较

目的 比较三种数字乳腺摄影系统(DR,PCM,CR)在自动曝光控制(AEC)模式下成像性能的差异.方法 使用不同厚度的PASMAM-1054模体和CDMAM3.4模体,以AEC模式分别在DR、PCM和CR系统进行摄影;测量腺体平均剂量(AGD);由三位观察者分析模体的X线影像,计算CDMAM 3.4模体的IQF值;采用SAS 9.1软件,广义线性模型统计分析方法,比较三套系统总体影像质量之间的差异.结果 PASMAM-1054模体分析结果,DR与PCM图像质量差异无统计学意义(P=0.3960),DR、PCM图像质量都优于CR(P=0.0024);CDMAM 3.4模体的影像质量DR优于PCM(P＜0.05),PCM优于CR(P=0.0003).结论 在本实验的三套数字乳腺成像系统中,DR与PCM系统的成像性能相对较好,不仅影像质量较高,而且具有较低的AGD;CR系统的AGD虽然较低,但是影像质量相对较低,综合成像能力不如DR和PCM系统.     

超低管电流三维自适应迭代剂量降低重建CT猪结肠成像质量与辐射剂量

目的 探讨超低管电流三维自适应迭代剂量降低(AIDR3D)重建CT猪结肠成像的图像质量与辐射剂量。方法 制作10段猪结肠息肉模型,每段猪结肠黏膜设有30枚直径1~15 mm的结节样模拟息肉。对所有模型均采用640层CT机进行扫描,管电压120 kVp,电流剂量分别为10、20、30、40、50 mAs。并获得滤波反投影(FBP)和AIDR3D重建图像,不同管电流及重建方法组合10组数据:A组(10 mA,FBP)、B组(10 mAs,AIDR3D)、C组(20 mAs,FBP)、D组(20 mAs,AIDR3D)、E组(30 mAs,FBP)、F组(30 mAs,AIDR3D)、G组(40 mAs,FBP)、H组(40 mAs,AIDR3D)、I组(50 mAs,FBP)、J组(50 mAs,AIDR3D)。测算图像的噪声、SNR及CNR作为定量指标,并对图像质量进行主观定性评分。以有效辐射剂量为指标比较各组图像的辐射剂量。结果 相同管电流条件下,AIDR3D图像的噪声低于FBP图像,SNC及CNR均高于FBP图像(P均<0.05)。D组与I组图像的噪声(P=0.052)、SNR(P=0.129)及CNR(P=0.053)差异均无统计学意义。B组图像的噪声(P=0.002)高于I组,SNR及CNR均低于I组(P均<0.001)。相同管电流条件下,AIDR3D图像的质量评分高于FBP图像(P均<0.05)。D组与I组的图像质量评分差异无统计学意义(P=0.121)。B组的图像质量评分低于I组(P<0.001)。 与I组(50 mAs,FBP)比较,D组(20 mAs,AIDR3D)的有效辐射剂量降低了59.90%,差异有统计学意义(P<0.05)。结论 超低管电流(20 mAs)扫描结合AIDR3D重建的猪结肠CT图像质量可媲美常规低管电流(50 mAs)扫描结合FBP重建的图像质量,并有效减低辐射剂量。     

SAFIRE重建算法对胸部CT图像质量和辐射剂量的影响

目的 利用仿真胸部体模,比较原始数据域迭代重建(SAFIRE)算法与滤波反投影(FBP)算法对胸部CT图像质量和辐射剂量的影响。方法 在新双源CT(Somatom definition flash CT)设备上预设80、100、120 kV三组管电压值,采用自动毫安秒care dose 4D技术对仿真胸部体模进行扫描,分别用FBP及SAFIRE重建算法(等级1~5)重建图像,比较胸部不同组织结构的噪声及CT值,并由2名放射科医师独立评价图像质量。每组扫描结束后,记录CT剂量加权指数(CTDIvol)和剂量长度乘积(DLP),计算并比较有效剂量。结果 相同扫描参数检查时,SAFIRE重建算法较FBP算法图像噪声明显降低(P<0.05);不同扫描参数检查时,无论FBP算法或SAFIRE重建算法,图像噪声均随管电压增加而降低;胸部各组织结构的噪声会随重建算法和管电压改变而发生变化;100 kV/SAFIRE(等级3)的主观和客观图像质量指标均优于120 kV/FBP,且辐射剂量降低37.61%。结论 胸部CT扫描中,采用SAFIRE重建算法能有效提高图像质量,降低辐射剂量。     

乳腺计算机X射线摄影图像质量和剂量最优化研究

目的 比较数字乳腺系统中手动曝光与自动曝光控制(AEC)下图像质量的差异,观察图像后处理在改善图像质量和降低受检者辐射剂量方面的作用。方法 分别选用CDMAM 3.4模体和TORMAM模体,在一套乳腺CR系统中选取5个不同厚度,每一个厚度分别为1次全自动曝光和3次手动曝光,手动曝光的剂量分别为AEC剂量的80%、60%和40%。由3名放射技师对模体影像进行2次评分,一次直接对原始图像评分;另一次对图像进行后处理以符合最佳显示条件并评分。比较手动低剂量曝光的影像与AEC曝光的影像质量的差异。结果 CDMAM 3.4模体中影像质量因子(IQF)测值表明,经过后处理的图像质量优于未处理时,部分低剂量图像的质量经过处理后优于AEC曝光剂量的图像。对于不同厚度的模体,通过手动改变曝光参数降低曝光量以及图像后处理,可降低受检者辐射剂量20%~60%。在TORMAM模体中,图像后处理对于纤维丝细节和圆形细节改善显著(P<0.001),而对于颗粒群细节无明显改善(P=0.74)。结论 乳腺CR数字摄影中,通过图像后处理可以改善图像质量,并在保持图像质量的同时降低受检者辐射剂量。     

胸部低剂量CT辅助诊断新型冠状病毒肺炎

目的 探讨胸部低剂量CT（LDCT）辅助诊断新型冠状病毒肺炎（COVID-19）的临床应用价值。方法 收集50例咽拭子新型冠状病毒（2019-nCoV）核酸检测阳性的COVID-19患者。首次胸部CT采用常规剂量扫描（常规剂量组），随访胸部CT采用LDCT扫描方案（LD组），对2组图像质量进行评价。采用Kappa检验分析2名医师评价2组图像质量结果的一致性，比较2组图像质量及2种CT扫描方案X线有效辐射剂量（ED）。结果 2名医师图像质量评分一致性较高（Kappa=0.65，P<0.05）LD组与常规剂量组之间图像质量差异无统计学意义（Z=-0.93，P=0.35）。LD组ED[（2.43±0.66）mSv]较常规剂量组[（4.02±1.03）mSv]减少约39.55%（t=0.85，P<0.01）。结论 胸部LDCT可用于临床筛查和辅助诊断COVID-19，图像质量可满足临床诊断要求，且能降低辐射剂量，具有重要临床应用价值。     

Radiation exposure and dose reduction measures in cardiac CT

Noninvasive visualization of the heart by CT is highly accurate and useful, but its association with ionizing radiation and the potential risk of cancer induction has raised concerns. Dose-saving algorithms, new CT scanners, and scanning techniques have been developed to effectively reduce the amount of radiation exposure without deterioration of image quality. Furthermore, additional strategies for dose reduction can be pursued in daily practice following the ALARA (as low as reasonably achievable) principle. However, there still is a high additional dose-saving potential in a consequent application of dose reduction measures, and we recommend individually adapted scan protocols to obtain cardiac CT studies with optimal diagnostic image quality and lowest possible radiation dose.     

Dose Optimization in Lumbar Spine Radiographic Examination by Air Gap Method at CR and DR Systems: A Phantom Study

ObjectiveThis study aims at investigating the feasibility of replacing an antiscatter grid with an air gap to achieve dose reduction for lumbar spine radiography while retaining image quality at an acceptable diagnostic level.MethodsFrontal and lateral projections of lumbar spine radiographic examinations were performed on an anthropomorphic phantom. Nongrid images of both the computed radiography (CR) and digital radiography (DR) systems with air gap thickness ranging from 0 to 25 cm were produced and compared with their corresponding grid images. Dose measurements using thermoluminescent dosimeters at the ovary and testes regions of the phantom were conducted. The image quality of all the images was evaluated by five radiographers using image quality score and visual grading analysis tests. Data on dose measurements and image quality tests were input for statistical analysis. The dose area product (DAP) of all the examinations was recorded and input for the computation of effective doses using a PC-based Monte Carlo program (PCXMC 2.0; STUK, Helsinki, Finland).ResultsSignificant dose reduction effects on the ovaries of 60.2%–74.1% and 55.1%–73.3% were found, respectively, at the frontal and lateral projections of nongrid lumbar spine examinations compared with their corresponding grid ones in both the CR and DR systems. Results on the image quality score and visual grading analysis tests showed that nongrid images with 10-cm and 5-cm of air gap thicknesses respective to the frontal and lateral images of the lumbar spine were rated with the highest scores. In general, a dose reduction effect using the air gap method was found to be more pronounced in the CR system compared with the DR system. Nevertheless, the CR system delivered a 2.4–4.5 times higher ovary dose respective to the frontal and lateral projections of lumbar spine examinations compared with the DR system.ConclusionsTen and 5 centimeters were found to be the optimal air gap thicknesses respective to the frontal and lateral lumbar spine radiographic examinations of the tested Rando phantom (Alderson Laboratories, Stamford, CT) in both the CR and DR systems. Significant dose reduction effects on both the ovary and testes regions of the nongrid examinations were shown. The effective dose computed from PCMCX 2.0 reflected that the risk of cancer induction was halved when an antiscatter grid was replaced by the nongrid method with an optimal air gap thickness in the tested examinations. Further reduction on cancer risk could be achieved by using DR instead of the CR system.