Influence of tube voltage and current on in-line phase contrast imaging using a microfocus x-ray source

In-line x-ray phase contrast imaging has attracted much attention due to two major advantages： its effectiveness in imaging weakly absorbing materials, and the simplicity of its facilities. In this paper a comprehensive theory based on Wigner distribution developed by Wu and Liu [Med. Phys. 31 2378-2384 （2004）] is reviewed. The influence of x-ray source and detector on the image is discussed. Experiments using a microfocus x-ray source and a CCD detector are conducted, which show the role of two key factors on imaging： the tube voltage and tube current. High tube current and moderate tube voltage are suggested for imaging.

Single-shot grating-based x-ray differential phase contrast imaging with a modified analyzer grating

X-ray grating interferometer has attracted widely attention in the past years due to its capability in achieving x-ray phase contrast imaging with low brilliance source. However, the widely used phase stepping information extraction method reduces system stability and prolongs data acquisition time by several times compared with conventional x-ray absorption- based imaging. The mechanical stepping can be avoided by using a staggered grating, but at the cost of low vertical spatial resolution. In this paper, employing a modified staggered grating and the angular signal radiography, we proposed a single-shot grating-based x-ray differential phase contrast imaging with decent vertical spatial resolution. The theoretical framework was deduced and proved by numerical experiments. Absorption, phase, and scattering computed tomography can be performed without phase stepping. Therefore, we believe this fast and highly stable imaging method with decent resolution would be widely applied in x-ray grating-based phase contrast imaging.

Cosine fitting radiography and computed tomography

A new method in diffraction-enhanced imaging computed tomography （DEI-CT） that follows the idea developed by Chapman et al. [Chapman D, Thomlinson W, Johnston R E, Washburn D, Pisano E, Gmur N, Zhong Z, Menk R, Arfelli F and Sayers D 1997 Phys. Med. BioL 42 2015] in 1997 is proposed in this paper. Merged with a ＂reverse projections＂ algorithm, only two sets of projection datasets at two defined orientations of the analyzer crystal are needed to reconstruct the linear absorption coefficient, the decrement of the real part of the refractive index and the linear scattering coefficient of the sample. Not only does this method reduce the delivered dose to the sample without degrading the image quality, but, compared with the existing DEI-CT approaches, it simplifies data-acquisition procedures. Experimental results confirm the reliability of this new method for DEI-CT applications.

Non-Linear Phase Tomography Based on Fréchet Derivative

Phase imaging coupled to micro-tomography acquisition has emerged as a powerful tool to investigate specimens in a non-destructive manner. While the intensity data can be acquired and recorded, the phase information of the signal has to be “retrieved” from the data modulus only. Phase retrieval is an ill-posed non-linear problem and regularization techniques including a priori knowledge are necessary to obtain stable solutions. Several linear phase recovery methods have been proposed and it is expected that some limitations resulting from the linearization of the direct problem will be overcome by taking into account the non-linearity of the phase problem. To achieve this goal, we propose and evaluate a non-linear algorithm for in-line phase micro-tomography based on an iterative Landweber method with an analytic calculation of the Fréchet derivative of the phase-intensity relationship and of its adjoint. The algorithm was applied in the projection space using as initialization the linear mixed solution. The efficacy of the regularization scheme was evaluated on simulated objects with a slowly and a strongly varying phase. Experimental data were also acquired at ESRF using a propagation-based X-ray imaging technique for the given pixel size 0.68 μm. Two regularization scheme were considered: first the initialization was obtained without any prior on the ratio of the real and imaginary parts of the complex refractive index and secondly a constant a priori value was assumed on ?. The tomographic central slices of the refractive index decrement were compared and numerical evaluation was performed. The non-linear method globally decreases the reconstruction errors compared to the linear algorithm and is achieving better reconstruction results if no prior is introduced in the initialization solution. For in-line phase micro-tomography, this non-linear approach is a new and interesting method in biomedical studies where the exact value of the a priori ratio is not known.

Phase Contrast Micro-Computed Tomography of Biological Sample at SSRF

In line X-ray phase contrast micro-computed tomography （IL-XPCT）, which can be implemented at third generation synchrotron radiation sources or by using a micro-focus X-ray tube, is a powerful technique for non-destructive, high-resolution investigations of a broad variety of materials. At the Shanghai Synchrotron Radiation Facility （SSRF）, the X-ray Imaging and Biomedical Applications Beamline was built and started regular user operation in May 2009. Both qualitative （without phase retrieval） and quantitative （with phase retrieval） three-dimensional IL-XPCT experimental techniques have been established at the beamline IL-XPCT experiments of a test sample （plastic pipes） used to evaluate the technique, and of a biological sample （locust） at the beamline are reported. Two series of images, qualitative and quantitative, including tomographic slices and three-dimensional rendering images were obtained. In qualitative images, there is a strong edge-enhancement which leads to very clear sample contours, while in quantitative images, the edge-enhancement fades but quantitative measurement of sample＇s phase information could be achieved. The experiments demonstrate that the combination of qualitative and quantitative images is useful for biological sample studies.

Digital microstructure insights to phase evolution and thermal flow properties of hydrates by X-ray computed tomography

Natural gas-hydrates are valuable energy resource with rich deposits,and their thermal transport and thermal dynamic mechanical behaviors significantly affect the long-term production process and phase change-based thermal energy storage characteristics of these energy resources.This paper aims to propose novel relations to predict the thermophysical properties,to investigate the hydrate phase evolution in microstructures,and to study the thermal transport and thermal dynamic mechanical properties.Hydrates formation experiments in sandpack samples and ultrasonic wave tests are conducted with the aid of X-ray CT imaging.Digitalization microstructures models and variables are defined to describe the hydrate phase evolution,and novel relations are proposed to accurately predict the thermophysical properties based on the microporosity and ultrasonic wave velocities.The thermal transport and thermal dynamic mechanical properties in microstructures with hydrate,water,residuary pore and grain phases are studied.Results show that the average errors of porosity,P-wave and S-wave velocities between the experimental data and computed results by the proposed relations are less than 5%,indicating the accuracy and reliability of the proposed method.The temperature fraction decreases with increasing underground temperature and decreasing hydrate saturation.The thermal stress and thermal displacement increase as temperature and hydrate saturation increase.There are strong anisotropy for the temperature fraction,thermal stress and thermal displacement during the thermal transport of hydrates.

Contrast ultrasound in hepatocellular carcinoma at a tertiary liver center: First Indian experience

AIM: To assess the role of contrast enhanced ultrasonography in evaluation of hepatocellular carcinoma (HCC) at the first Indian tertiary liver center. METHODS: Retrospective analysis of contrast enhanced ultrasound (CEUS) examinations over 24 mo for diagnosis, surveillance, characterization and follow up of 50 patients in the context of HCC was performed. The source and indication of referrals, change in referral rate, accuracy and usefulness of CEUS in a tertiary liver center equipped with a 64 slice dual energy computer tomography (CT) and 3 tesla magnetic resonance imaging (MRI) were studied. Sonovue (BR1, Bracco, Italy, a second generation contrast agent) was used for contrast US studies. Contrast enhanced CT/MRI or both were performed in all patients. The findings were taken as a baseline reference and correlation was done with respect to contrast US. Contrast enhanced MRI was performed using hepatocyte specific gadobenate dimeglumine (Gd-BOPTA). Iomeron (400 mg; w/v) was used for dynamic CT examinations. RESULTS: About 20 (40%) of the examinations were referred from clinicians for characterization of a mass from previous imaging. About 15 (30%) were performed for surveillance in chronic liver disease; 5 (10%) examinations were performed for monitoring lesions after radiofrequency ablation (RFA); 3 (6%) were post trans-arterial chemoembolization (TACE) assessments and 3 (6%) were patients with h/o iodinated contrast allergy. About 2(4%) were performed on hemodynamically unstable patients in the intensive care with raised alpha fetoprotein and 2(4%) patients were claustrophobic. The number of patients referred from clinicians steadily increased from 12 in the first 12 mo of the study to 38 in the last 12 mo. CEUS was able to diagnose 88% of positive cases of HCC as per reference standards. In the surveillance group, specificity was 53.3% vs 100% by CT/MRI. Post RFA and TACE specificity of lesion characterization by CEUS was 100% in single/large mass assessment, similar to CT/MRI. For non HCC lesions such as regenerative and dysplastic nodules, the specificity was 50% vs 90% by CT/MRI. The positive role of CEUS in imaging spectrum of HCC included a provisional urgent diagnosis of an incidentally detected mass. It further led to a decrease in time for further management. A confident diagnosis on CEUS was possible in cases of characterization of an indeterminate mass, in situations where the patient was unfit for CT/MRI, was allergic to iodinated contrast or had claustrophobia, etc.CEUS was also cost effective, radiation free and an easy modality for monitoring post RFA or TACE lesions. CONCLUSION: CEUS is a valuable augmentation to the practice of ultrasonography, and an irreplaceable modality for confounding cases and interpretation of indeterminate lesions in imaging of HCC.

Correlation of the CT values of abdominal aorta,renal artery and renal cortex with its thickness on 64-MDCT contrast enhanced imagesCorrelation of the CT values of abdominal aorta,renal artery and renal cortex with its thickness on 64-MDCT contrast enhance

Objective:To investigate the correlation of abdominal aorta CT value,renal artery CT value and renal cortex thickness with renal cortex CT value on contrast enhanced 64-slice CT images.Methods:96patients(50 men and 46women;16~74years)with normal kidney function,which was confirmed by kidney function test were enrolled in this study,including bilateral kidneys of 92cases and unilateral kidney of 4cases(total of 188kidneys;92left,96right).After intravenous(IV)injection of contrast agent the kidneys of the selected patients were scanned by MDCT.The scans were performed in arterial,venous and 3min delayed phases.All statistical analyses were performed by using IBM SPSS 20.0.Graphs were generated using Graph Pad Prism 5software.Quantitative data were presented as mean±standard deviation,while qualitative data were presented as frequency(%).P<0.05was considered to be statistically significant.Results:The mean renal cortex thickness was(5.19±0.81)mm in all kidneys.In the arterial phase,a statistically significant positive correlation between renal cortex CT values and abdominal aortic CT values was showed(r=0.584;P<0.001).A statistically significant positive correlation between renal cortex CT values and renal cortex thickness was demonstrated(r=0.533,P<0.0001).Likewise,there was a positive correlation between renal cortex CT value and renal artery CT values(r=0.43,P<0.001).Conclusion:It is a promising approach to assess the individual kidney function by measuring abdominal aorta CT value,renal artery CT value,renal cortex CT value and renal cortex thickness using contrast MDCT.

Nanoparticles:Untying the Gordian Knot in Conventional Computed Tomography Imaging

X-ray computed tomography(CT)imaging plays an essential role in disease diagnosis due to its noninvasive,painless mode and superior penetration depth.However,the resolution of the soft tissue and minor lesions remains limited.And the disadvantages of conventional contrast agents,such as their inefficient targeting capability,poor biocompatibility,and short circulation times,are considered intractable in clinical use.To overcome these“Gordian knots,”nanoparticles(NPs)for CT imaging have been developed.The advantages of NPs are their exceptionally high sensitivity to X-ray,better imaging performance in vivos and even therapeutic effects.In particular,based on various designs,NP contrast agents composed of different materials integrate multiple imaging modalities,make up for the inadequacy of a single imaging type,and thus provide more accurate information for diagnosis.This review focuses on NPs for X-ray CT imaging and their multifunctional designs.Some perspectives of crucial problems and prospective challenges are also discussed.

低剂量对比剂联合生理盐水在MSCT双期脑血管成像中的应用

目的探讨低剂量对比剂加生理盐水冲洗对MSCT双期脑血管成像图像质量的影响。方法60例受试者平均分为两组:A组:低剂量对比剂+生理盐水;B组:76ml对比剂。以Test-Bolus确定脑动、静脉期延迟扫描时间,对两组受试者行MSCT双期扫描,比较CT动脉成像(CTA)、CT静脉成像(CTV)图像质量差异。结果Test-Bolus测试血管循环时间组间差异无统计学意义,CTA脑动脉分支显示及静脉干扰评分、动脉最大强化均值、动静脉最大强化差值的组间差异均无统计学意义。CTV脑静脉窦最大强化均值的差异不显著,B组均匀性优于A组(P<0.001),深浅静脉最大强化均值大于A组(P=0.02)。静脉显示评分差异无统计学意义。A组静脉窦、深浅静脉与动脉最大强化差值均大于B组(P<0.001,P<0.001),CTV期动脉强化干扰程度低于B组(P<0.001)。结论低剂量对比剂加生理盐水冲洗不影响脑CT血管图像质量,同时能显著降低CT静脉成像期的动脉干扰,不影响脑静脉清晰显示。

聚合物泡沫结构及密度分布的相衬CT表征技术

阐述了利用X射线相衬成像技术研究高分子有机泡沫材料微观结构的原理及方法,理论分析及实验结果表明,X射线相衬成像方法可以在相当大的程度上提高低Z聚合物泡沫材料的成像衬度。将相衬成像技术与计算机层析成像技术相结合,获得了泡沫样品的3维骨架结构分布,同时,提出利用统计切片骨架"粒子"质心分布的方法来表征其密度分布均匀性。结果说明,该方法能够在微观层次上实现对泡沫样品3维密度分布的完备表征。

双能量CT成像评估胃癌分化程度的价值

目的:探讨双能量CT成像对评估胃癌分化程度的价值。方法:2012年12月-2014年12月本院41例胃癌患者行双源CT双能量腹部双期增强扫描,测量100、120和140kV图像及40~140keV各单能量图像(共14组图像)上胃癌病灶在动脉期和门静脉期图像上的CT值,并计算静脉期与动脉期CT值的差值(△CT)。利用t检验分析中高分化胃癌与低分化胃癌间CT值及△CT值的差异。结果:中高分化胃癌与低分化胃癌在各组中动脉期、静脉期图像上CT值的差异均无统计学意义(P>0.05);在120、140kV以及80~130keV图像上,中高分化胃癌与低分化胃癌间△CT的差异有统计学意义(P值分别为0.043、0011、0.035、0.016、0.013、0.017、0.030和0.046)。结论:双源CT双能量增强扫描有助于评估胃癌的分化程度。

肝细胞癌微观结构的X线相衬CT成像研究

目的肝细胞癌(HCC)是最常见的恶性肿瘤之一,本文探讨X线相衬CT(PCCT)在HCC微观结构成像中的应用价值,有助于进一步了解该疾病的发展机制。资料与方法采集HCC组织8例,按病理表现分为中分化组(4例)和低分化组(4例)。在上海同步辐射装置的BL13W1线站进行相衬成像。重建HCC组织中的微观结构,与病理切片对比分析,并应用三维纹理分析方法评估两组中肝细胞排列结构的变化。结果相衬CT成像清晰地显示了HCC组织中的纤维胶原、肿瘤边缘微血管、窦样毛细血管等特征结构的二维和三维特征,与病理切片表现一致。三维纹理分析结果显示低分化组肝细胞的排列结构较中分化组发生了显著变化(P<0.05)。结论相衬CT成像可清晰地显示HCC微观结构的二维和三维图像特征,并为其结构的定量分析提供了参考,在HCC的研究中具有潜在的应用和推广价值。

脑胶质瘤在CT平扫及三期增强中的图像表现特征分析

目的分析脑胶质瘤的CT平扫及三期增强扫描典型影像特征,同时探讨CT平扫及三期增强扫描图像对脑胶质瘤的显示质量。方法选取我院2016年5月-2018年6月我院经手术病理确诊的脑胶质瘤患者76例,患者均行CT平扫及三期增强扫描,对患者的临床及影像学资料进行收集,分析脑胶质瘤患者的肿瘤大小、分布、以及与周围组织间的关系等CT影像特征。结果 CT平扫图像上4例表现为高密度、16例表现为低密度、9例表现为中等密度、6例表现为混杂密度、3例表现为等密度,其中45例伴钙化现象出现,3例伴出血。肿瘤边界多较模糊,形态多不规则,肿瘤出现明显占位现象,且周围水肿区显像明显。CT增强扫描三期,肿瘤均出现不同程度的强化,且水肿区增强扫描后表现为多环状轻度或重度强化,部分可有强化的壁结节影出现。结论 CT平扫及三期增强扫描对脑间质瘤显示良好,具有典型的脑胶质瘤影像特征,且对肿瘤形态、大小以及其对周期组织的侵犯情况显示清楚,能对脑胶质瘤进行较为准确的定位、定性。

多层螺旋CT增强和门静脉重建成像对门静脉癌栓的诊断优势

目的:探讨16层螺旋CT增强扫描和门静脉重建技术多层面重建(multiple planar reformation,MPR)、最大密度投影(maximum intensityprojection,MIP)、容积重建(volume rendering,VR)的联合应用在门静脉癌栓中的诊断价值.方法:52例门静脉癌栓患者,采用16层螺旋CT行平扫、动脉期、门脉期及平衡期扫描.扫描参数:层厚2.5 mm,重建间距:0.625 mm,注射速率为3.5-4 mL/s,对比剂注入:80-100 mL,扫描时间为25-30 s,45-60 s和120 s.影像重建技术包括:VR、MPR和MIP,图像重建由1名诊断医生完成,另由2名诊断医生评价门静脉癌栓的范围、形态以及侧支循环情况.结果:动脉期癌栓呈不均匀强化35例(67.3%);47例门静脉增粗及充盈缺损(90.4%),门静脉管壁强化19例(36.5%),侧支循环形成13例(25%),门静脉受压13例(25%),门静脉海绵样变4例(7.7%),动-静脉瘘4例(7.7%).门静脉重建技术对门静脉癌栓的显示:MPR显示52例(100%),MIP显示43例(82.7%),VR显示39例(75%).结论:CT增强结合门静脉重建技术对门静脉癌栓显示更加全面,具有重要的临床应用价值.

乳腺癌相衬成像与病理对照

常规X线摄影术在分辨软组织尤其是腺体和肿瘤的差异时,存在一定困难。本研究使用相位衬度成像来解决这一问题。相位衬度成像利用X线经过物体时的相位变化进行成像,具有软组织成像高对比度的特点。本研究使用相位衬度CT成像技术,对恶性乳腺肿瘤进行观察。并与病理切片结果相对照。结果显示,相衬CT能够发现乳腺癌的典型组织学和影像学特征,并能形成与大体病理组织切片的良好对应。相位衬度成像在乳腺癌样本成像上具备了"准病理"水平对比度的成像效果,有望用于临床环境。

应用类同轴相衬CT比较3种根管封闭剂的根充效果

目的:应用类同轴相衬CT(PCCT)评估3种根管封闭剂(AHPlus、iRootSP、GuttaFlow)结合热垂直加压充填技术的根充效果。方法:选取完整离体前磨牙32颗,随机分为4组,A组不用任何封闭剂,B组AHPlus根管封闭剂,C组iRootSP根管封闭剂,D组GuttaFlow根管封闭剂,4组均使用相同的根管预备和根管充填方法。待封闭剂完全固化后行PCCT成像检测,测量根尖1/3未充填空隙的百分比,定量分析根管充填的效果。结果:根尖1/3未充填空隙体积百分比A组大于B、C、D组(P<0.01),B组大于C组和D组,D组大于C组(P<0.05)。结论:iRootSP根尖封闭性优于GuttaFlow和AHPlus,而Gut-taFlow根尖封闭性优于AHPlus。

基于折射角的稀疏投影角度相衬CT图像重建

已有基于X射线吸收衬度机制的计算机断层成像(CT)技术很难对由轻元素构成的弱吸收物质进行高质量成像。X射线相位衬度CT成像是对弱吸收物质具有超高分辨率的一种CT技术,但该技术成像时间长、所需X射线辐射剂量大,不利于临床推广应用,因此,研究稀疏投影角度条件下的X射线相位衬度CT图像重建问题,基于压缩感知图像重建理论,使用折射角信息减少X射线辐射剂量,提出一种X射线相位衬度CT图像重建算法。实验结果表明,与滤波反投影算法相比,该算法在稀疏投影角度下可以得到较高质量的重建图像,在实际数据实验中能获得较高的峰值信噪比和数值准确性。

肝脏门静脉期CT增强的影响因素与对策

随着CT技术的发展,尤其是近几年双能CT的出现,不仅提高了影像质量,而且能够实现物质定量分析,极大拓展了临床应用范围,但同时也对优化应用提出了新的挑战。在上腹部检查中由于肝脏双重供血的特点造成了增强检查的特殊性,这突出体现在门静脉期影像质量难以达到预期而降低诊断可靠性上。因此,分析影响门静脉期增强的对比剂、病人和CT扫描等方面因素,总结在提高影像质量的同时降低对比剂剂量和辐射剂量的研究进展,并展望基于双能CT的个性化的上腹部增强检查计划设计方案。

关节软骨X线相位对比成像技术研究进展

同步辐射相位对比成像技术是近年来新兴的一种成像技术,具有高亮度、高分辨力和高度相干等成像优势,可以对关节软骨进行无创性检测,并能直观地显示软骨的微观组织学形态结构特征。相位对比成像技术能显示软骨表层纤维化、小裂隙形成等骨关节炎早期病理变化,对疾病的早期干预和治疗评估具有重要意义。就各种相位对比成像技术原理、基础研究及其进展予以综述。