Characterization of the phase-contrast radiography edge-enhancement effect in a cabinet x-ray system

The purpose of this study was to demonstrate that a commercially available cabinet x-ray system is capable of phase-contrast radiography (PC-R) and to evaluate the effect of different system parameters on the degree of edge enhancement. An acrylic plastic edge phantom was imaged at different tube potentials (25-60 kV) and in different geometries (variable object-to-detector distances, R(2), at a constant source-to-detector distance, R(1) + R(2)). In addition, the effect of noise on the perceived edge enhancement was studied as a function of exposure time. Our results show that a modest degree of phase contrast can be achieved in an unmodified cabinet x-ray system. In addition, the particular system evaluated allowed low-noise PC-R images to be obtained with short (6 s or less) exposures. These results suggest that with appropriate geometric choices PC-R is already available to a wide range of research scientists for use in both small-animal and human-specimen experiments.     

Quantification of the effect of system and object parameters on edge enhancement in phase-contrast radiography

The purpose of this study was to evaluate the effects of system parameters (focal spot size, tube voltage, geometry, detector resolution, and image noise) and object characteristics (edge gradient/ shape, composition, thickness, and overlying attenuating material) upon the edge enhancement effect in phase-contrast radiography. Each variable of interest was adjusted and images of a 3 mm lucite phantom were obtained with the other variables remaining constant. A microfocus x-ray source coupled to a CCD camera with an intensifying screen was used to acquire the digital images. Two parameters of image analysis were used to quantify the effects. The edge enhancement index (EEI) was used to measure the absolute degree of edge enhancement, while the edge enhancement to noise ratio (EE/N) was used to measure the conspicuity of the edge enhancement relative to image noise. Little effect on EEI was seen from tube voltage, object thickness, overlying attenuating material, while focal spot size and system geometry demonstrated measurable effects upon the degree of edge enhancement. It was also shown that while the edge enhancement effect over straight edges is highly dependent upon how the edge aligns with the x-ray beam, rounded edges, which better model biological objects, do not suffer from this dependence and the EEI reaches its maximal level at any alignment. Decreasing detector resolution diminished the EEI slightly, but even with pixel sizes of 0.360 x 0.360 mm edge enhancement effects were readily visible. The effect of image noise on EE/N was evaluated using different exposure times showing an expected improvement with longer exposure time with EE/N approaching a plateau at 5 min. Many of the parameters that will go into the design of a future PC-R imaging system have been quantified in terms of their effect on the degree of edge enhancement in the acquired image. These results, taken together, indicate that either a specimen or even clinical breast imaging system could be created with currently available technology. The major limitation to a clinical system would be the low x-ray flux from the microfocal x-ray source.     

Dual focal-spot imaging for phase extraction in phase-contrast radiography

The purpose of this study was to evaluate dual focal spot imaging as a method for extracting the phase component from a phase-contrast radiography image. All measurements were performed using a microfocus tungsten-target x-ray tube with an adjustable focal-spot size (0.01 mm to 0.045 mm). For each object, high-resolution digital radiographs were obtained with two different focal spot sizes to produce matched image pairs in which all other geometric variables as well as total exposure and tube kVp were held constant. For each image pair, a phase extraction was performed using pixel-wise division. The phase-extracted image resulted in an image similar to the standard image processing tool commonly referred to as "unsharp masking" but with the additional edge-enhancement produced by phase-contrast effects. The phase-extracted image illustrates the differences between the two images whose imaging parameters differ only in focal spot size. The resulting image shows effects from both phase contrast as well as geometric unsharpness. In weakly attenuating materials the phase-contrast effect predominates, while in strongly attenuating materials the phase effects are so small that they are not detectable. The phase-extracted image in the strongly attenuating object reflects differences in geometric unsharpness. The degree of phase extraction depends strongly on the size of the smallest focal spot used. This technique of dual-focal spot phase-contrast radiography provides a simple technique for phase-component (edge) extraction in phase-contrast radiography. In strongly attenuating materials the phase-component is overwhelmed by differences in geometric unsharpness. In these cases the technique provides a form of unsharp masking which also accentuates the edges. Thus, the two effects are complimentary and may be useful in the detection of small objects.     

上颌第一前磨牙X线法髓腔物理量

目的:探讨上颌第1前磨牙X线片法髓腔物理量方面的数据.方法:用X线平行投照法拍摄实体牙颊舌向和近远中向X线片牙影像,根据本研究对髓腔根管定的分型标准对根管进行分型.用电脑配套的柯达成像系统测量X线片牙的髓高、髓宽、根中颊径、根中舌径、根尖颊径和根尖舌径.用SPSS17.0软件统计处理X线片牙的髓腔物理量值.结果:100颗上颌第1前磨牙中X线片牙根管有6种类型,Ⅰ-1-1型占33％,Ⅰ-2-2型占17％,Ⅰ-2-1型占13％,Ⅰ-1-2型占4％,Ⅰ-2-1-2型占3％,Ⅱ-2-2型占30％.X线片牙的测量值(mm)显示,髓高3.09±1.18,髓宽3.88±0.61,根中颊径1.76±1.18,根中舌径0.59±0.34,根尖颊径0.79±0.39,根尖舌径0.35±0.28.髓腔物理量各测值差异均存在统计学意义.结论:上述结果说明,湖北地区上颌第1前磨牙根管类型主要是Ⅰ-1-1型,Ⅰ-2-2型,Ⅱ-2-2型.X线片牙物理量测值经相关及回归分析,如果有相关性的配对项,可用回归方程中的自变量值(X)来推测因变量的值(Y),为口腔临床实践提供髓腔物理量方面的未知数据.     

Paediatric entrance doses from exposure index in computed radiography

Over the last two years we have evaluated paediatric patient doses in projection radiography derived from exposure level (EL) in computed radiography (CR) in a large university hospital. Entrance surface air kerma (ESAK) for 3501 paediatric examinations was calculated from the EL, which is a dose index parameter related to the light emitted by the phosphor-stimulable plate, archived in the Digital Imaging and Communications in Medicine (DICOM) header of the images and automatically transferred to a database using custom-built dedicated software. Typical mean thicknesses for several age bands of paediatric patients was estimated to calculate ESAK from the EL values, using results of experimental measurements with phantoms for the typical x-ray beam qualities used in paediatric examinations. Mean/median ESAK values (in microGy) for the age bands of <1 year, 1-5 years, 6-10 years and 11-15 years have been obtained for chest without a bucky: 51/41, 57/34, 91/54 and 122/109; chest with a bucky (for only the last three age bands): 114/87, 129/105 and 219/170; abdomen: 119/91, 291/225, 756/600 and 1960/1508 and pelvis: 65/48, 455/314, 943/707 and 2261/1595. Sample sizes of clinical images used for the (indirect) measurements were 1724 for chest without a bucky, 799 for chest with a bucky, 337 for abdomen and 641 for pelvis. The methodology we describe could be applicable to other centres using CR as an imaging modality for paediatrics. Presently, this method is the only practical approach to automatically extract parameters contained in the DICOM header, for the calculation of patient dose values for the CR modality.     

Quantification of wall shear stress in large blood vessels using Lagrangian interpolation functions with cine phase-contrast magnetic resonance imaging

Arterial wall shear stress is hypothesized to be an important factor in the localization of atherosclerosis. Current methods to compute wall shear stress from magnetic resonance imaging (MRI) data do not account for flow profiles characteristic of pulsatile flow in noncircular vessel lumens. We describe a method to quantify wall shear stress in large blood vessels by differentiating velocity interpolation functions defined using cine phase-contrast MRI data on a band of elements in the neighborhood of the vessel wall. Validation was performed with software phantoms and an in vitro flow phantom. At an image resolution corresponding to in vivo imaging data of the human abdominal aorta, time-averaged, spatially averaged wall shear stress for steady and pulsatile flow were determined to be within 16% and 23% of the analytic solution, respectively. These errors were reduced to 5% and 8% with doubling in image resolution. For the pulsatile software phantom, the oscillation in shear stress was predicted to within 5%. The mean absolute error of circumferentially resolved shear stress for the nonaxisymmetric phantom decreased from 28% to 15% with a doubling in image resolution. The irregularly shaped phantom and in vitro investigation demonstrated convergence of the calculated values with increased image resolution. We quantified the shear stress at the supraceliac and infrarenal regions of a human abdominal aorta to be 3.4 and 2.3 dyn/cm², respectively. © 2002 Biomedical Engineering Society. PAC2002: 8761-c, 8719Uv     

Quantification of nanoscale nuclear refractive index changes during the cell cycle

Intrigued by our recent finding that the nuclear refractive index is significantly increased in malignant cells and histologically normal cells in clinical histology specimens derived from cancer patients, we sought to identify potential biological mechanisms underlying the observed phenomena. The cell cycle is an ordered series of events that describes the intervals of cell growth, DNA replication, and mitosis that precede cell division. Since abnormal cell cycles and increased proliferation are characteristic of many human cancer cells, we hypothesized that the observed increase in nuclear refractive index could be related to an abundance or accumulation of cells derived from cancer patients at a specific point or phase(s) of the cell cycle. Here we show that changes in nuclear refractive index of fixed cells are seen as synchronized populations of cells that proceed through the cell cycle, and that increased nuclear refractive index is strongly correlated with increased DNA content. We therefore propose that an abundance of cells undergoing DNA replication and mitosis may explain the increase in nuclear refractive index observed in both malignant and histologically normal cells from cancer patients. Our findings suggest that nuclear refractive index may be a novel physical parameter for early cancer detection and risk stratification.     

Quantification of the effect of gas exchange on the slope of phase III

It was previously shown that gas exchange could contribute to the rising slope of phase III of the single-breath nitrogen (SB-N2) test. This study was done to quantify this role. We studied eight normal volunteers with a series of SB-N2 derived tests where the RV gas was progressively changed from room air to 90% O2 and 10% N2, by 10% increments in O2 and 10% decreases in N2 concentrations (i.e. room air, 70% N2 30% O2, 60% N2 40% O2, etc.). A similar series of SB-R (single-breath reversed gradients test) derived tests was done. Here the RV contained 100% O2 by previous washout, while the inspired gas was changed by 105 steps from room air to 10% N2 90% O2. We therefore have a situation where dilutional N2 gradients change with the % N2, in either the RV or the inspired gas. However, the alveolar volume loss remains the same for all tests. The mean +/- SD slope of phase III in the SB-N2 series for our eight subjects decreased from 0.87 +/- 0.25 with room air to 0.14 +/- 0.07 with 10% N2 90% O2, while its steepness in the SB-R series decreased from 0.62 +/- 0.23 with the inspired room air to 0.11 +/- 0.06 with the final inspiration being 10% N2 90% O2. From these data, we could calculate that the mean % contribution of gas exchange to the slope of phase III was 10.2%.     

Studies of performance of antiscatter grids in digital radiography: effect on signal-to-noise ratio

We developed a theoretical model which describes the improvement of signal-to-noise ratio (SNR) by a grid in digital radiography. The model takes into account the effects of spatial variations in the scatter-to-primary ratio and in the large-area contrast over an image with structured background on quantum noise, and the effects of noise in the imaging system such as electronic noise and digitization noise. Based on the theoretical model, we analyzed the effects of these factors on the SNR when a grid is employed. We performed experimental measurements to evaluate the improvement in the SNR by a grid when quantum noise is the dominant noise source. It was found that the measured SNR improvement factor due to quantum noise agreed closely with that determined from the measured transmission values of a grid, as predicted from our theoretical model. In order to evaluate the relative performance of grids with various geometric design parameters for digital radiographic systems, we employed Monte Carlo calculations and determined the transmission values of a number of grids under various scatter conditions. The calculated SNR improvement factor, due to quantum noise, correlated well with the measured improvement of the SNR by the grids. Our model predicts that the SNR improvement factor depends strongly on the local contrast ratio and also on the scatter-to-primary ratio. The SNR improvement factor is higher in the underpenetrated regions than in the well-penetrated regions of an image.     

基于相位衬度成像的小鼠肺肿瘤三维可视化研究

目的肿瘤的早期发现对患者意义重大。鉴于相位衬度成像对于如肺部这样的软组织成像效果显著,本文提出利用相位衬度成像技术,以微米尺度的空间分辨对肿瘤进行成像,并定量分析,早期发现肿瘤。方法在KM小鼠肺部原位接种人肺癌细胞,培育10d后取出肺组织,利用上海同步辐射光源进行相位衬度成像获取投影图像,拍摄结束后对样本进行切片、HE染色,并光学显微镜观察病理切片。然后利用滤波反投影对获取的投影图进行CT断层重建,并通过病理切片对比验证肿瘤位置,最后通过Amira软件进行三维模型的建立。结果重建出了清晰的三维模型,在模型上可以发现小肿瘤结节的存在,并测量得出该肿瘤体积为0．655mm3。结论相位衬度成像对软组织分辨率高,能发现体积较小的肿瘤．对肿瘤的早期发现有一定意义。     

The effect of time of day on apnoea index in the sleeping rat

This study tested the hypothesis that apnoea index would be greater during daytime sleep than nighttime sleep in the rat. Electroencephalogram and electromyogram were monitored via biotelemetry implant and respiration was measured using whole body plethysmography in six male rats in two separate 34h recording sessions per animal. Apnoeas were classified as "spontaneous" or "post-sigh". Daily average spontaneous apnoea index was 35 times greater (p<0.0001) during rapid eye movement (REM) sleep than in non-REM (NREM) sleep. In contrast, daily average post-sigh apnoea index was not significantly greater in REM sleep than in non-REM (NREM) sleep (p=0.39). There was a greater post-sigh apnoea index during daytime REM than during nighttime REM (p=0.043) but REM-related spontaneous apnoea index was unaffected by time of day. There was no day to night difference in spontaneous apnoea index or post-sigh apnoea index during NREM sleep. Respiratory variability (coefficient of variation for breath duration and tidal volume) was not affected by time of day in REM or NREM sleep. We conclude that the circadian timing system has no effect on apnoea index during NREM sleep in the rat, but it may influence the propensity for post-sigh apnoea during REM sleep.     

Optimal kvp selection for dual-energy imaging of the chest: evaluation by task-specific observer preference tests

Human observer performance tests were conducted to identify optimal imaging techniques in dual-energy (DE) imaging of the chest with respect to a variety of visualization tasks for soft and bony tissue. Specifically, the effect of kVp selection in low- and high-energy projection pairs was investigated. DE images of an anthropomorphic chest phantom formed the basis for observer studies, decomposed from low-energy and high-energy projections in the range 60-90 kVp and 120-150 kVp, respectively, with total dose for the DE image equivalent to that of a single chest radiograph. Five expert radiologists participated in observer preference tests to evaluate differences in image quality among the DE images. For visualization of soft-tissue structures in the lung, the [60/130] kVp pair provided optimal image quality, whereas [60/140] kVp proved optimal for delineation of the descending aorta in the retrocardiac region. Such soft-tissue detectability tasks exhibited a strong dependence on the low-kVp selection (with 60 kVp providing maximum soft-tissue conspicuity) and a weaker dependence on the high-kVp selection (typically highest at 130-140 kVp). Qualitative examination of DE bone-only images suggests optimal bony visualization at a similar technique, viz., [60/140] kVp. Observer preference was largely consistent with quantitative analysis of contrast, noise, and contrast-to-noise ratio, with subtle differences likely related to the imaging task and spatial-frequency characteristics of the noise. Observer preference tests offered practical, semiquantitative identification of optimal, task-specific imaging techniques and will provide useful guidance toward clinical implementation of high-performance DE imaging systems.     

颈椎间盘突出程度与颈椎X线片相关指标测量值的相关性研究

目的探讨单节段脊髓型颈椎病患者颈椎X线片相关指标与椎间盘突出导致的颈脊髓压迫严重程度的相关性。方法回顾性分析2012年8月—2014年3月安徽医科大学第一附属医院脊柱外科诊治的60例单节段脊髓型颈椎病患者的临床资料,均为男性,年龄42~65岁,平均(54.8依9.3)岁。在颈椎MRI矢状位成像上按照颈脊髓受压的比例( E值)分为Ⅰ组、Ⅱ组及Ⅲ组。在颈椎MRI横断面成像上测量并计算颈髓横切面积( S1)与有效椎管横切面积( S0)的比值,以此判断椎间盘突出程度;在不同体位颈椎X线摄片上测量责任椎间隙的活动度值(B值)、椎间隙前缘高度( D值)、颈椎C2~7 Cobb角及椎间孔面积( M值)等相关指标。采用直线相关回归分析颈椎间盘突出程度与各观测指标之间的相关性。结果3组间S1/S0值、E值、B值、D值、C2~7 Cobb角和M值差异均有统计学意义(F值分别为44.187、112.789、7.232、3.778、3.232、15.813,P值均<0.05)。随着S1/S0值的增加,E值、B值、D值、C2~7 Cobb角和M值均逐渐减小,提示责任椎间隙E值、B值、D值、C2~7 Cobb角、M 值与 S1/S0值均呈负相关性( R 值分别为-0.821、-0.581、-0.378、-0.419、-0.576,P值均<0.05)。经多元线性回归分析,B 值、D 值、M 值是 S1/S0的3个独立影响因素, S1/S0值的预测方程为^Y=118.955-1.348X1-2.850X2-0.541X3(复相关系数R=0.742,决定系数R2=0.550,F=22.841,P<0.01),回归模型有统计学意义。结论不同体位颈椎X线摄片的相关指标B值、D值、M值是影响脊髓型颈椎病椎间盘退变突出程度的独立因素,对评估单节段脊髓型颈椎间盘突出的严重程度有一定的诊断价值;采用D值、B值及M值为3个自变量指标,可对椎间盘突出进行预测。     

Use of storage phosphor imaging plates in portal imaging and high-energy radiography: the intensifying effect of metallic screens on the sensitivity

The sensitivity of storage phosphor imaging plates (SPIP) at megavolt photon energies (60Co, 6-, 10-, and 18-MV radiotherapy beams) is studied both experimentally and by Monte Carlo radiation transport calculations. In addition, the same techniques are used to investigate the intensifying effect of metal screens on the sensitivity of the SPIP. The results provide evidence that the sensitivity of the SPIPs is proportional to the absorbed energy in the phosphor layer per cGy. The spectral sensitivity is calculated for photon energies between 10 keV and 20 MeV for various SPIP-screen combinations.     

Experimental validation of the Wigner distributions theory of phase-contrast imaging

Recently, a new theory of phase-contrast imaging has been proposed by Wu and Liu [Med. Phys. 31, 2378-2384 (2004)]. This theory, based upon Wigner distributions, provides a much stronger foundation for the evaluation of phase-contrast imaging systems than did the prior theories based upon Fresnel-Kirchhoff diffraction theory. In this paper, we compare results of measurements made in our laboratory of phase contrast for different geometries and tube voltages to the predictions of the Wu and Liu model. In our previous publications, we have used an empirical measurement (the edge enhancement index) to parametrize the degree of phase-contrast effects in an image. While the Wu and Liu model itself does not predict image contrast, it does measure the degree of phase contrast that the system can image for a given spatial frequency. We have found that our previously published experimental results relating phase-contrast effects to geometry and x-ray tube voltage are consistent with the predictions of the Wu and Liu model.