Different degrees of atherosclerosis detected by backscattered ultrasound: an in vitro study on fixed human aortic walls

The aim of the study was to establish whether ultrasonic backscattered signals may characterize the atherosclerotic process, providing a quantitative assessment of severity. Measurements on aortic specimens were made in vitro by a transducer acting as transmitter and receiver. Two different indices were measured, one based on peak amplitude value (Vmax) and the other on fast Fourier transform (FFT) analysis of ultrasonic reflected signal (IBI). Two hundred fixed aortic wall specimens (50 normal, 50 fatty streaks, 50 fibrofatty, and 50 calcific) were first characterized ultrasonically and then pathologically, both macroscopically (before ultrasonic study) and histologically (after it). Differentiation of normal, fibrofatty and calcific specimens was achieved using Vmax. Values obtained in fatty streaks overlapped with normal wall but significantly differed from values of fibrofatty and calcific subsets. The results with IBI were similar except that the difference between normal and fibrofatty specimens was not statistically significant. Such changes in acoustic behavior of atherosclerotic walls could be due to increased deposition of highly echogenic biological materials, such as collagen, cholesterol crystals (in fibrofatty specimens), and calcium salts (in calcific ones). Therefore, backscattered signals appear to provide in vitro simple parameters indicative of changes in the arterial wall structure due to the atherosclerotic process.     

Acceleration time in normal fetal umbilical artery at term and its relationship to the cord blood hematocrit

The purpose of this study was to test the hypothesis that the acceleration time (AT) of the fetal umbilical artery remains constant at term for normal pregnancies. In addition, we also examined whether the AT has any correlation with umbilical cord blood hematocrit (Hct). In total, 539 normal-term fetuses with menstrual ages (MA) ranging from 37 weeks to 42 weeks were enrolled in a cross-sectional design. The AT of the fetal umbilical artery was measured prior to delivery using a high-resolution, real-time Doppler scanner. All were delivered within 2 days of the ultrasound examination. At parturition, blood from the umbilical vein was collected and the red cell indices, including the Hct, were determined. The results indicated that the mean values of AT of the umbilical artery remained constant during normal-term pregnancies from 37 weeks to 42 weeks, menstrual age (mean: 0.104 sec, SE: 0.001 sec, n = 539). Although the AT was thought to be affected by the Hct, the AT had no correlation with umbilical venous Hct (n = 539, r = 0.002, p > 0.05). This constant value of the AT may be used as a reference for fetal physiology and perinatal medicine. © 1995 John Wiley & Sons, Inc.     

Statistical analysis of high frequency ultrasonic backscattered signals from Basal cell carcinomas

A statistical approach was implemented in the study of histologic characteristics from ex vivo basal cell carcinomas, based on the properties of backscattered acoustic waves, for the purpose of evaluating the method as a diagnostic tool. The study was developed using an ultrasound biomicroscope working at a frequency of 45 MHz. The parameters examined were signal-to-noise ratio (SNR), and shape parameters from the Weibull (b_W) and generalized gamma (c_GG and υ_GG) probability density functions. Twenty-seven carcinomatous skin samples were obtained from volunteer patients and classified into two groups (BCC1 and BCC2) based on the distribution patterns of their tumor nests; also, seven non-tumoral samples were used for comparative purposes. Significant differences between groups were obtained for all studied parameters. The successful differentiation between some tissue groups suggests its potential use for carcinoma characterization.     

Measurements of ultrasonic backscattered spectral centroid shift from spine in vivo: methodology and preliminary results

Ultrasonic backscatter measurements from vertebral bodies (L3 and L4) in nine women were performed using a clinical ultrasonic imaging system. Measurements were made through the abdomen. The location of a vertebra was identified from the bright specular reflection from the vertebral anterior surface. Backscattered signals were gated to isolate signal emanating from the cancellous interiors of vertebrae. The spectral centroid shift of the backscattered signal, which has previously been shown to correlate highly with bone mineral density (BMD) in human calcaneus in vitro, was measured. BMD was also measured in the nine subjects' vertebrae using a clinical bone densitometer. The correlation coefficient between centroid shift and BMD was r = -0.61. The slope of the linear fit was -160 kHz / (g/cm(2)). The negative slope was expected because the attenuation coefficient (and therefore magnitude of the centroid downshift) is known from previous studies to increase with BMD. The centroid shift may be a useful parameter for characterizing bone in vivo.     

心脏运动影响多普勒血流速度频谱测定的机制实验研究

目的 探讨模拟心脏与模拟血流同步及非同步运动时,心脏运动对多普勒血流速度频谱测定的影响机制。方法 用自行设计的仪器,使模拟心脏运动和模拟血液的脉动频率按一定的相位同步,非同步,观察当这两种运动同时发生时,模拟心脏运动对模拟血流速度频谱的影响及它们之间的定量关系。结果 当模拟心脏和模拟血流做同步或非同步运动时,所记录到的模拟血流频谱为模拟心脏运动和模拟血流按速度矢量相加规律所组成的复合波,而模拟心脏运动所产生的多普勒频移信号的振幅和频率都未改变且与血流信号并存于频谱中,结论 我们通常所谓的血流速度频谱实际上是血细胞在心脏内流动速度和心脏运动速度的矢量和,即两项运动的复合频谱,即便当模拟心脏和模拟血流做同步或非同步运动时也是如此。     

应用超声微泡直接测量微小血管血流速度

目的应用超声微泡直接、非侵入性测量微小血管的血流速度。方法体外实验：用硅胶管建立一种模拟血流的体外模型,应用谐波超声追踪超声微泡在管内的流动,并录像。用“DFY型超声图像定量分析诊断仪”分析每帧中微泡的位置,以微泡的移动距离除以时间,得到微泡的移动速度。体内实验：建立9只大鼠直肠癌移植瘤模型,用与体外实验相同的方法测量大鼠直肠癌移植瘤内微小血管的血流速度。肿瘤切片HE染色,显微镜下测量肿瘤血管内径。结果体外实验：在体外模型中的血流标准速度分别为37．14mm／s,21．01mm／s和4．35mm／s,应用本法测得的血流速度为（37．03±2．45）1mm／s、（24．40±2．10）mm／s和（4．86±0．45）mm／s,两者间无统计学差异。体内实验：在肿瘤模型中所测得的小血管内血流速度为5．38～20．82mm／s;HE染色发现9个肿瘤外周的最大血管内径平均为（142．76±24．03）μm,肿瘤内部的最大血管内径平均为（40．82±11．17）μm。这些小血管在常规多普勒超声下不能被探及。结论本实验测试了一种直接测量小血管的血流速度的新技术。结果表明,应用超声微泡可以准确测量小血管内的血流速度。经过对自动化跟踪技术的优化,这种新技术极有可能成为临床上非侵入性直接测量小血管血流速度的有效工具。     

Multigate Doppler measurements of ultrasonic attenuation and blood hematocrit in human arteries

A clinically applicable method for noninvasive measurement of hematocrit based on 20 MHz multigate Doppler ultrasound was developed. The ultrasound attenuation coefficient in blood is obtained by measuring the power of the signal coming from gates at different depths. A robust averaging method is introduced, which provides stable and repeatable results by using the echo signals from all depths inside the vessel. In vitro measurements have been done on porcine blood with hematocrit ranging from 3.0% to 65.0%. Steady and pulsatile flow conditions have been simulated using a peristaltic pump. The attenuation coefficient indicated the linear relation to hematocrit. The resulting correlation coefficient was R = 0.999 for the continuous blood flow and R = 0.992 for pulsatile flow. In vivo measurements have been performed in the brachial artery in 43 patients with hematocrit in the range of 32.0% to 49.3%. The mean absolute error has been 3.24% with a standard deviation of 3.72%.     

Relation of in vivo blood flow to ultrasound echogenicity

The mechanism of echogenicity of flowing blood during real-time ultrasonography was investigated experimentally in vivo by scanning venous and arterial blood and venous blood subjected to varying degrees of obstruction. Luminal echoes were more intense in flowingblood of the vena cava than in aortic blood of dogs. Vena cava and portal echoes increased in intensity as flow was decreased progressively by obstruction. We believe that an important cause of echogenicity of flowing blood is red cell aggregation which is greatest at low shear rates (low flow velocity). Echogenicity decreases with increase in shear rate (higher flow velocity) which causes red cell disaggregation.     

On the measurement of the mean velocity of blood flow over the cardiac cycle using Doppler ultrasound

A number of modern duplex scanners now have facilities for determining volumetric blood flow through intact vessels. The methods these machines use to arrive at an answer must presuppose a number of conditions which may not be met in practice. This paper examines the effect that nonuniform insonation of the target blood vessel (using continuous wave or wide-gate pulsed ultrasound) has on the mean velocity, as determined using mean, root mean square (RMS) and maximum frequency processors. It is shown that for a given beam/vessel geometry the error is dependent only on the shape of the mean component of the velocity profile which, depending on the arterial site, may be flat, parabolic or intermediate. Mean processors may overestimate the mean velocity of established flow by up to 33%, but this could be turned to advantage when it is impracticable to insonate a vessel uniformly. Maximum frequency processors are of value when either plugflow or fully established flow of low pulsatility is present in the target vessel. In the first case the mean flow is the same as the maximum flow, while in the second the mean flow is half the time averaged maximum flow, irrespective of the size and shape of the ultrasound beam. RMS processors are probably best avoided in volumetric flow measurement applications.     

Doppler ultrasound compatible plastic material for use in rigid flow models

A technique for the rapid but accurate fabrication of multiple flow phantoms with variations in vascular geometry would be desirable in the investigation of carotid atherosclerosis. This study demonstrates the feasibility and efficacy of implementing numerically controlled direct-machining of vascular geometries into Doppler ultrasound (DUS)-compatible plastic for the easy fabrication of DUS flow phantoms. Candidate plastics were tested for longitudinal speed of sound (SoS) and acoustic attenuation at the diagnostic frequency of 5 MHz. Teflon was found to have the most appropriate SoS (1376 +/- 40 m s(-1) compared with 1540 m s(-1) in soft tissue) and thus was selected to construct a carotid bifurcation flow model with moderate eccentric stenosis. The vessel geometry was machined directly into Teflon using a numerically controlled milling technique. Geometric accuracy of the phantom lumen was verified using nondestructive micro-computed tomography. Although Teflon displayed a higher attenuation coefficient than other tested materials, Doppler data acquired in the Teflon flow model indicated that sufficient signal power was delivered throughout the depth of the vessel and provided comparable velocity profiles to that obtained in the tissue-mimicking phantom. Our results indicate that Teflon provides the best combination of machinability and DUS compatibility, making it an appropriate choice for the fabrication of rigid DUS flow models using a direct-machining method.     

Physical properties of tissues relevant to arterial ultrasound imaging and blood velocity measurement

A review was undertaken of physical phenomena and the values of associated physical quantities relevant to arterial ultrasound imaging and measurement. Arteries are multilayered anisotropic structures. However, the requirement to obtain elasticity measurements from the data available using ultrasound imaging necessitates the use of highly simplified constitutive models involving Young's modulus, E. Values of E are reported for healthy arteries and for the constituents of diseased arteries. It is widely assumed that arterial blood flow is Newtonian. However, recent studies suggest that non-Newtonian behavior has a strong influence on arterial flow, and the balance of published evidence suggests that non-Newtonian behavior is associated primarily with red cell deformation rather than with aggregation. Hence, modeling studies should account for red cell deformation and the shear thinning effect that this produces. Published literature in healthy adults gives an average hematocrit and high-shear viscosity of 0.44 +/- 0.03 and 3.9 +/- 0.6 mPa.s, respectively. Published data on the acoustic properties of arteries and blood is sufficiently consistent between papers to allow compilation and derivation of best-fit equations summarizing the behavior across a wide frequency range, which then may be used in future modeling studies. Best-fit equations were derived for the attenuation coefficient vs. frequency in whole arteries (R(2) = 0.995), plasma (R(2) = 0.963) and blood with hematocrit near 45% (R(2) = 0.999), and for the backscatter coefficient vs. frequency from blood with hematocrit near 45% (R(2) = 0.958).     

体外模拟实验研究心脏运动对频谱多普勒血流速度测定的影响

目的：通过体外模拟实验，研究心脏运动对频谱多普勒血流速度测定的影响。方法：设计一套仪器，使它模拟心脏运动的速度和频率并使在其内流动的模拟血液的流速和频率及这两种运动的开启和停止时间都分别可控，观察模拟血流的频谱多普勒在模拟心脏运动影响下的变化及它们之间量的关系。结果：在模拟心脏运动作用下，原来的模拟血流波形已不存在，代之以模拟心脏运动和模拟血流控速度矢量相加规律所组成的复合波，而模拟心脏运动所产生的多普勒频移信号的振幅和频率都未改变且与上述血流信号并存于频谱中，结论：通常所谓的血流速度频谱实际上是血细胞在心脏内流动速度和心脏运动速度的矢量和。即两项运动的复合频谱。所以，为减少误差，在用多普勒血流速度频谱测定血流参数时，应考虑校正问题。     

Characterization of in vitro healthy and pathological human liver tissue periodicity using backscattered ultrasound signals

This work studied the periodicity of in vitro healthy and pathologic liver tissue, using backscattered ultrasound (US) signals. It utilized the mean scatterer spacing (MSS) as a parameter of tissue characterization, estimated by three methods: the spectral autocorrelation (SAC), the singular spectrum analysis (SSA) and the quadratic transformation method (SIMON). The liver samples were classified in terms of tissue status using the METAVIR scoring system. Twenty tissue samples were classified in four groups: F0, F1, F3 and F4 (five samples for each). The Kolmogorov-Smirnov test (applied on group pairs) resulted as nonsignificant (p > 0.05) for two pairs only: F1/F3 (for SSA) and F3/F4 (for SAC). A discriminant analysis was applied using as parameters the MSS mean (MSS) and standard deviation (sigmaMSS), the estimates histogram mode (mMSS), and the speed of US (mc(foie)) in the medium, to evaluate the degree of discrimination among healthy and pathologic tissues. The better accuracy (Ac) with SAC (80%) was with parameter group (MSS, sigmaMSS, mc(foie)), achieving a sensitivity (Ss) of 92.3% and a specificity (Sp) of 57.1%. For SSA, the group with all four parameters showed an Ac of 75%, an Ss of 78.6% and an Sp of 66.70%. SIMON obtained the best Ac of all (85%) with group (MSS, mMSS, mc(foie)), an Ss of 100%, but with an Sp of 50%.     

The production of blood cell stasis and endothelial damage in the blood vessels of chick embryos treated with ultrasound in a stationary wave field

Blood cell flow can be arrested in living tissue by exposing it to ultrasound in a stationary wave field. The cells form bands at half wavelength intervals in the blood vessels. The process is generally reversible, and during dissociation the hands assume a parabolic profile in vessels where flow is laminar. Under optimum conditions, in the chick embryo, the minimum intensity required for stasis is less than 0·5 Wcm^?2 at 3 MHz with continuous irradiation. The threshold intensity varies with the type, size and orientation of the vessel, and with the heart rate. Electron microscopy reveals damage to some of the endothelial cells lining the embryonic vessels in which stasis has occurred. Methods of avoiding stasis are suggested and the mechanisms of stasis are discussed.     

Noninvasive ultrasonic estimation of brachial artery blood flow.

Ultrasonic instrumentation based on the Doppler phenomenon fulfills the requirement that a blood flowmeter should sense a variabel which is a function of the volume of blood moved through a blood vessel in situ. The blood flow velocity waveform recorded noninvasively from the brachial artery in the antecubital fossa was used as basis for quantitatively estimating a stroke flow index. The method used in these experiments was reproducible in 31 volunteer subjects studied; the first and second brachial artery stroke flow indices determined on different days had a correlation coefficient of 0.909. The calculated minute flow index ranged from 32 to 95 ml in these subjects. A clinical application was explored by making serial measurements before and after operation in 64 patients submitting to 68 open heart operations. A significant reduction in the brachial artery blood flow velocity was recorded postoperatively in 21 of these patient. The brachial artery stroke flow index has potential value as an objective measure of cardiovascular instability.     

献血45d后献血者部分生化和免疫指标变化的研究

目的分析无偿献血者献血后部分生化免疫参数的变化及其对机体功能恢复能力的影响。方法选择生活、工作环境相同,饮食种类和运动量基本一致的献血者250名,年龄18—26岁,按血液采集标准步骤采集外周静脉血,分别测定其总蛋白、白蛋白、总淋巴细胞(CD3)、T辅助细胞(CD4)和T抑制细胞(CD8)浓度(数),45d后再次采集血液测定相同参数并进行比较。结果与献血前比较,所测定的献血后外周血中的生化指标变化无统计学意义(P>0.05);血液中总蛋白和白蛋白浓度均在正常范围内,与献血前比较其浓度明显增加(P<0.05);四色流式细胞仪检测显示,献血后CD3、CD4和CD8均显著增高(P<0.01),CD4/CD8比值变化无统计学意义(P>0.05);此外,还显示献400ml者的总蛋白、白蛋白和总淋巴细胞数有高于献200ml者的趋势。结论献血能启动献血者机体应激反应系统,蛋白合成增加,T细胞亚群比例升高,使机体进入新的平衡状态。     

Quantitative ultrasound of skeletal muscle: reliable measurements of calibrated muscle backscatter from different ultrasound systems

Widespread implementation of quantitative muscle ultrasonography in assessing skeletal muscle pathology is limited by an inability to replicate results between different ultrasound systems. We have developed a measurement of skeletal muscle pathology, calibrated muscle backscatter (cMB), which should be reproducible between different ultrasound systems. We compared the reliability of grayscale and cMB measurements between different ultrasound systems, configurations and region-of-interest (ROI) sizes. cMB of skeletal muscle was reliably measured (intraclass correlation coefficient [ICC] ≤0.98) despite very dissimilar grayscale levels (ICC ≤0.54). cMB reliability was highest between systems using similar settings (ICC: 0.82–0.98) and was lowest when transducer type varied (ICC: 0.47–0.71). Reliability was better from ROIs spanning a narrow range of depths compared with larger ranges. cMB measurements are more reliable than grayscale between different ultrasound systems and configurations. Measuring cMB could improve widespread implementation of quantitative ultrasound in assessments of skeletal muscle pathology.     

频谱多普勒超声诊断椎基底动脉供血不足的价值

目的 探讨椎基底动脉系统脑血流量和椎基底动脉收缩期峰值流速在频谱多普勒超声诊断椎基底动脉供血不足(VBI)中的价值.方法 将107例临床怀疑椎基底动脉供血不足患者分为三组:重度VBI组、轻一中度VBI组和非VBI组.分别检测椎动脉和基底动脉二维图像和血流频谱,比较椎动脉、基底动脉收缩期峰值流速和椎基底动脉系统脑血流量在诊断椎基底动脉供血不足中的差异.结果 椎动脉和基底动脉收缩期峰值流速在重度VBI组患者中明显低于轻-中度VBI组,差异有统计学意义(P＜0.05);在轻-中度VBI组患者中低于非VBI组,但差异无统计学意义(P＞0.05).结论 脑血流量在判定患者是否为椎基底动脉供血不足及程度上有诊断价值,可以作为超声诊断VBI的有效指标.