Optimum scan spacing for three-dimensional ultrasound by speckle statistics

A technique is introduced to determine the spacing between acquired two-dimensional (2-D) planes necessary to maintain resolution in the scan direction while maximizing scan speed for 3-D ultrasound (US) imaging. We performed statistical analysis on a series of 3-D scans of agar blocks with different image spacings, quantifying speckle size (S(c)) as the full-width half-maximum (FWHM) of the autocovariance function. S(c) was approximately constant at small 2-D image-plane spacings, but increased after the scan spacing surpassed some optimum point. Optimum spacing ranged between 0.075 and 0.4 mm, increasing with the axial depth and the number of focal zones. This latter dependence is a result of successive sampling by the US machine and the digitizer at unequal rates, as demonstrated through an analysis of the noise power spectra. This analysis predicted that S(c) may be significantly reduced by using a transducer sampling rate that is twice the digitization rate. This technique permits the calculation of the most efficient scan spacings for 3-D US imaging.     

Deviations from Rayleigh statistics in ultrasonic speckle

The statistics of speckle patterns in ultrasound images have potential for tissue characterization. In "fully developed speckle" from many random scatterers, the amplitude is widely recognized as possessing a Rayleigh distribution. This study examines how scattering populations and signal processing can produce non-Rayleigh distributions. The first order speckle statistics are shown to depend on random scatterer density and the amplitude and spacing of added periodic scatterers. Envelope detection, amplifier compression, and signal bandwidth are also shown to cause distinct changes in the signal distribution.     

Laser speckle imaging of intra organ drug distribution

Laminar flow in arteries causes streaming and uneven distribution of infused agents within the organ. This may lead to misinterpretation of experimental results and affect treatment outcomes. We monitor dynamical changes of superficial cortical blood flow in the rat kidney following different routes of administration of the vasoconstrictor angiotensin II. Our analysis reveals the appearance of large scale oscillations of the blood flow caused by inhomogeneous intra organ drug distribution.OCIS codes: (120.6150) Speckle imaging, (170.1470) Blood or tissue constituent monitoring, (170.5380) Physiology     

Burr hole evacuation for infratentorial subdural empyema

Infratentorial empyema is a life threatening condition and constitutes a neurosurgical emergency. Purulent mastoiditis and medial otitis is the most common origin and a thorough eradication of the purulent foci is mandatory. Decompression craniectomy has been primarily advised in the literature as the gold standard of the surgical treatment but burr hole evacuation when there the lack of cerebellar edema is less invasive and deemed equally efficient in the few reported cases. This is the report of a seventeen year old female who presented in a comatose state due to infratentorial empyema with acute hydrocephalus and who improved immediately after burr hole evacuation. Details of the surgical procedures are given. Mastoidectomy was completed, with the patient under combined antibiotherapy. She leads a normal life now, more than six years after surgery.     

慢性硬膜下血肿的钻孔引流治疗

目的:分析单孔钻颅引流术治疗慢性硬膜下血肿的手术经验及疗效。方法:回顾分析用单孔钻颅引流术治疗的60例慢性硬膜下血肿患者的临床资料。结果:60例患者均痊愈出院,颅脑CT复查示脑组织复张良好,随访中无复发及严重并发症病例。结论:单孔钻颅引流术治疗老年慢性硬膜下血肿的疗效确切,操作安全、简便,并发症少。     

Properties of acoustical speckle in the presence of phase aberration. Part I: First order statistics

The first order statistical properties of acoustical speckle patterns are studied as a function of several types of random and structured phase error. Such errors may arise from tissue velocity inhomogeneities or limitations in the acoustical imaging system. In this paper, we review the theory describing the statistical properties of speckle, describe a computer model which predicts the mean speckle brightness in the presence of phase aberrations, and report experiments in which we measure the effect of these aberrations on speckle brightness and variance. We find that the average speckle brightness is significantly reduced by even mild phase aberrations. The phase aberrations studied include focal point errors, random phase errors, and structured errors. Good agreement is found between experiment and computer simulation. We then discuss the implications of these results for imaging through aberrating media, tissue characterization and phase compensation methods.     

A zero-crossing strain estimator for elastography

A novel zero-crossing tracking strain estimator (ZCT) has been developed for elastography. This technique is based on tracking the zero-crossings between the pre- and postcompression A-lines, and does not require global or adaptive A-line stretching. For multicompression elastography, ZCT can be implemented as a tracking scheme, where a temporal track of the zero-crossings between successive radiofrequency (RF) A-lines is obtained, or as an averaging scheme, where a cumulation of the interframe strains is performed, to yield high elastographic signal-to-noise ratio (SNR). Other advantages of the scheme include fast processing and its potential to be implemented in hardware. The limitations of the technique are the need for small compression steps due to lack of robustness when large compression steps (> 3% applied compression) are used. Simulations and experiments were performed to illustrate its utility as an alternative strain-estimation technique. This technique provides lower SNR but higher contrast-to-noise ratio (CNR) than the conventional strain-estimation techniques in elastography.     

Local versus regional procurement and distribution of granulocytes

Granulocyte concentrates obtained by discontinuous flow centrifugation (DFC) and continuous flow centrifugation (CFC) were studied. The DFC granulocytes were obtained from a regional center and stored for 24 hours prior to transfusion. The CFC granulocytes were obtained locally and transfused within a few hours. Even at 24 hours, DFC granulocytes had significantly reduced bactericidal capacity, chemiluminescence, nitroblue tetrazolium reduction, chemotaxis and random mobility. Granulocyte kinetics utilizing DF32P and skin windows demonstrated the ability of DFC granulocytes to circulate and migrate into the tissues despite the in vitro abnormalities. Until effective storage techniques for granulocyte preservation became available, rapid transportation and processing from regional centers or local procurement of granulocytes is necessary to transfuse functional granulocytes.     

New microembolus size estimator for peripheral blood vessels

Several factors affecting the power of Doppler scattered signal and, consequently, microembolus size estimation, may be eliminated when assessing the microembolus size via multiple measurements. A new microembolus size estimator is proposed based on the ratio of microembolus scattering cross-section in two directions and for two emission frequencies. Theoretical considerations indicate that the estimation of size of microembolic elements should be independent of the spatial distribution of the wave intensity, tissue attenuation and hardware factors. The simulation results indicate that this estimation only slightly depends on the material of the microembolus and acoustic properties of blood. The experimental results indicate that the accuracy of median size estimation increases with microembolus size. The measurement error is less than 27% for microemboli with median diameter larger than 360 μm. The method is constrained to the estimation of microembolus size in the vessels of extremities.     

Choosing a model for laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is a real-time full-field non-invasive technique, which is broadly applied to visualize blood flow in biomedical applications. In its foundation is the link between the speckle contrast and dynamics of light scattering particles–erythrocytes. The mathematical form describing this relationship, which is critical for accurate blood flow estimation, depends on the sample’s light-scattering properties. However, in biological applications, these properties are often unknown, thus requiring assumptions to be made to perform LSCI analysis. Here, we review the most critical assumptions in the LSCI theory and simulate how they affect blood flow estimation accuracy. We show that the most commonly applied model can severely underestimate the flow change, particularly when imaging brain parenchyma or other capillary perfused tissue (e.g. skin) under ischemic conditions. Based on these observations and guided by the recent experimental results, we propose an alternative model that allows measuring blood flow changes with higher accuracy.     

An efficient speckle tracking algorithm for ultrasonic imaging

An efficient speckle tracking algorithm is proposed for motion estimation in ultrasonic imaging. Speckle tracking involves a matching process and a searching process. The matching process of the proposed algorithm is based on a Block Sum Pyramid algorithm that significantly reduces the computational complexity while maintaining the same accuracy as the conventional sum of absolute difference approach. The searching process, on the other hand, is based on a multilevel search strategy rather than the full-search strategy used by most conventional tracking methods. Both simulated speckle images and clinical breast images were used to test the performance of the proposed algorithm. The results show that the computation efficiency is improved by up to a factor of five over the conventional approach. The improved efficiency enables real-time or near-real-time implementation of motion estimation in ultrasonic imaging, which is particularly beneficial in areas such as blood flow estimation, elasticity imaging, speckle image registration, and strain compounding.     

基于空间统计学的贵州省甲型肝炎时空分布模式分析

目的 分析贵州省甲型肝炎（甲肝）时空分布模式,为贵州省制定有针对性的甲肝防控策略提供参考依据。方法 从传染病报告信息管理系统收集2009—2018年贵州省各县甲肝病例报告数据,利用空间自相关、时空扫描统计量等空间统计学方法分析甲肝的时空分布模式。结果 2009—2018年贵州省累计报告甲肝病例10 471例,年平均报告发病率为2.84/10万,报告发病率呈现下降趋势（趋势χ2=8 280.97,P<0.001）;2009—2018年贵州省甲肝发病整体存在空间聚集性,全局Moran’s I值介于0.055～0.310,除2011年,其余年份甲肝发病有空间自相关（P<0.05）,共探测到甲肝高–高聚集区44个,主要集中在黔中地区,低–低聚集区54个,主要集中黔东南地区;时空扫描结果显示,2009—2018年贵州省甲肝发病存在6个时空聚集区,每个聚集区差异均有统计学意义（P<0.05）,这些聚集区大部分位于贵阳市、黔南州、黔东南州、遵义市、铜仁市和毕节市的部分区（县）。结论 2009—2018年贵州省甲肝发病呈现显著的下降趋势,全省整体存在时空聚集性,聚集区主要集中在黔南州...     

Using historical vital statistics to predict the distribution of under-five mortality by cause

Background: Cause-specific mortality data is essential for planning intervention programs to reduce mortality in the under age five years population (under-five). However, there is a critical paucity of such information for most of the developing world, particularly where progress towards the United Nations Millennium Development Goal 4 (MDG 4) has been slow. This paper presents a predictive cause of death model for under-five mortality based on historical vital statistics and discusses the utility of the model in generating information that could accelerate progress towards MDG 4.Methods: Over 1400 country years of vital statistics from 34 countries collected over a period of nearly a century were analyzed to develop relationships between levels of under-five mortality, related mortality ratios, and proportionate mortality from four cause groups: perinatal conditions; diarrhea and lower respiratory infections; congenital anomalies; and all other causes of death. A system of multiple equations with cross-equation parameter restrictions and correlated error terms was developed to predict proportionate mortality by cause based on given measures of under-five mortality. The strength of the predictive model was tested through internal and external cross-validation techniques. Modeled cause-specific mortality estimates for major regions in Africa, Asia, Central America, and South America are presented to illustrate its application across a range of under-five mortality rates.Results: Consistent and plausible trends and relationships are observed from historical data. High mortality rates are associated with increased proportions of deaths from diarrhea and lower respiratory infections. Perinatal conditions assume importance as a proportionate cause at under-five mortality rates below 60 per 1000 live births. Internal and external validation confirms strength and consistency of the predictive model. Model application at regional level demonstrates heterogeneity and non-linearity in cause-composition arising from the range of under-five mortality rates and related mortality ratios.Conclusions: Historical analyses suggest that under-five mortality transitions are associated with significant changes in cause of death composition. Sub-national differentials in under-five mortality rates could require intervention programs targeted to address specific cause distributions. The predictive model could, therefore, help set broad priorities for interventions at the local level based on periodic under-five mortality measurement. Given current resource constraints, such priority setting mechanisms are essential to accelerate reductions in under-five mortality.     

On the potential of the Lagrangian speckle model estimator to characterize atherosclerotic plaques in endovascular elastography: in vitro experiments using an excised human carotid artery

Endovascular ultrasound (US) elastography (EVE) was introduced to supplement endovascular US echograms in the assessment of vessel lesions and for endovascular therapy planning. Indeed, changes in the vascular tissue stiffness are characteristic of vessel wall pathologies and EVE appears as a very appropriate imaging technique to outline the elastic properties of vessel walls. Recently, a model-based approach was proposed to assess tissue motion in EVE. It specifically consists of a nonlinear minimization algorithm that was adapted to speckle motion estimation. Regarding the theoretical framework, such an approach considers the speckle as a material property; this assumption then led to the derivation of the optical flow equations, which were suitably combined with the Lagrangian speckle model estimator to provide the full 2-D polar strain tensor. In this study, the proposed algorithm was validated in vitro using a fresh excised human carotid artery. The experimental setup consisted of a cardiovascular imaging system (CVIS) US scanner, working with a 30-MHz mechanical rotating single-element transducer, a digital oscilloscope and a pressuring system. A sequence of radiofrequency (RF) images was collected while incrementally adjusting the intraluminal static pressure steps. The results showed the potential of this 2-D algorithm to characterize and to distinguish an atherosclerotic plaque from the normal vascular tissue. Namely, the geometry as well as some mechanical characteristics of the detected plaque were in good agreement with histology. The results also suggested that there might exist a range of intraluminal pressures for which plaque detectability is optimal.     

Correction for spatial averaging in laser speckle contrast analysis

Practical laser speckle contrast analysis systems face a problem of spatial averaging of speckles, due to the pixel size in the cameras used. Existing practice is to use a system factor in speckle contrast analysis to account for spatial averaging. The linearity of the system factor correction has not previously been confirmed. The problem of spatial averaging is illustrated using computer simulation of time-integrated dynamic speckle, and the linearity of the correction confirmed using both computer simulation and experimental results. The valid linear correction allows various useful compromises in the system design.