A Dual-Phantom System for Validation of Velocity Measurements in Stenosis Models Under Steady Flow

A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.41 of silicone. Dynamic scaling was performed to correct for the increased viscosity of the PIV fluid compared with that of the ultrasound blood mimic. The degree of stenosis in the models pairs agreed to less than 1%. The velocities in the laminar flow region up to the peak velocity location agreed to within 15%, and the difference could be explained by errors in ultrasound velocity estimation. At low flow rates and in mild stenoses, good agreement was observed in the distal flow fields, excepting the maximum velocities. At high flow rates, there was considerable difference in velocities in the poststenosis flow field (maximum centreline differences of 30%), which would seem to represent real differences in hydrodynamic behavior between the two models. Sources of error included: variation of viscosity because of temperature (random error, which could account for differences of up to 7%); ultrasound velocity estimation errors (systematic errors); and geometry effects in each model, particularly because of imperfect connectors and corners (systematic errors, potentially affecting the inlet length and flow stability). The current system is best placed to investigate measurement errors in the laminar flow region rather than the poststenosis turbulent flow region. (E-mail: P.Hoskins@ed.ac.uk)     

A Rotating Cylinder Phantom for Flow and Tissue Color Doppler Testing

Ultrasound Doppler using two-dimensional (2D) techniques is commonly used to study blood flow and myocardial tissue motion. This use includes measurement of velocity and time intervals, often in relation to the electrocardiogram (ECG) signal. 2D Doppler is frequently considered a real-time technique but in reality the acquisition time can be as long as 200 ms per image. We have developed a test-phantom using a rotating cylinder to simulate blood flow and tissue motion in a whole sector or space angle to evaluate velocity and timing characteristics. The phantom can produce constant velocities for velocity testing, as well as accelerating movement for testing the timing characteristics of ultrasound systems. Our investigation shows that the cylinder phantom is especially suitable for timing measurements in 2D Doppler imaging and that time delays between the Doppler signals and the ECG signal exist in the tested ultrasound system. (E-mail: andrew.walker@ltv.se)     

Acquisition of 3-D Arterial Geometries and Integration with Computational Fluid Dynamics

A system for acquisition of 3-D arterial ultrasound geometries and integration with computational fluid dynamics (CFD) is described. The 3-D ultrasound is based on freehand B-mode imaging with positional information obtained using an optical tracking system. A processing chain was established, allowing acquisition of cardiac-gated 3-D data and segmentation of arterial geometries using a manual method and a semi-automated method, 3D meshing and CFD. The use of CFD allowed visualization of flow streamlines, 2-D velocity contours and 3-D wall shear stress. Three-dimensional positional accuracy was 0.17–1.8 mm, precision was 0.06–0.47 mm and volume accuracy was 4.4–15%. Patients with disease and volunteers were scanned, with data collection from one or more of the carotid bifurcation, femoral bifurcation and abdominal aorta. An initial comparison between a manual segmentation method and a semi-automated method suggested some advantages to the semi-automated method, including reduced operator time and the production of smooth surfaces suitable for CFD, but at the expense of over-smoothing in the diseased region. There were considerable difficulties with artefacts and poor image quality, resulting in 3-D geometry data that was unsuitable for CFD. These artefacts were exacerbated in disease, which may mean that future effort, in the integration of 3-D arterial geometry and CFD for clinical use, may best be served using alternative 3-D imaging modalities such as magnetic resonance imaging and computed tomography. (E-mail: P.Hoskins@ed.ac.uk)     

Blood flow occlusion via ultrasound image-guided high-intensity focused ultrasound and its effect on tissue perfusion

This study investigated the induction of tissue necrosis by arterial blood flow occlusion using ultrasound image-guided high-intensity focused ultrasound (HIFU). We constructed a prototype HIFU transducer in combination with an imaging probe that provided color Doppler imaging and ultrasound contrast imaging. The HIFU beam was aimed into a branch of the renal artery in vivo. The renal artery branches of eight rabbits were occluded by HIFU at an intensity of 4 kW/cm(2) (from 2 to 10 times of each sonication for 5 s). When the HIFU exposure was successful, complete cessation of blood flow was observed by color Doppler imaging with success rate of 100% (8/8). Furthermore, lack of perfusion was observed in the renal cortex with a contrast-enhanced image. Postmortem histologic evaluation showed a wedge-shaped area of infarction in six of seven cases, corresponding to the lack of the contrast medium in the ultrasound image. These results demonstrated that ultrasound image-guided HIFU can be used to induce arterial occlusion, thus producing infarction and necrosis of the perfused tissue.     

Anatomical flow phantoms of the nonplanar carotid bifurcation, part I: computer-aided design and fabrication

Doppler ultrasound is widely used in the diagnosis and monitoring of arterial disease. Current clinical measurement systems make use of continuous and pulsed ultrasound to measure blood flow velocity; however, the uncertainty associated with these measurements is great, which has serious implications for the screening of patients for treatment. Because local blood flow dynamics depend to a great extent on the geometry of the affected vessels, there is a need to develop anatomically accurate arterial flow phantoms with which to assess the accuracy of Doppler blood flow measurements made in diseased vessels. In this paper, we describe the computer-aided design and manufacturing (CAD-CAM) techniques that we used to fabricate anatomical flow phantoms based on images acquired by time-of-flight magnetic resonance imaging (TOF-MRI). Three-dimensional CAD models of the carotid bifurcation were generated from data acquired from sequential MRI slice scans, from which solid master patterns were made by means of stereolithography. Thereafter, an investment casting procedure was used to fabricate identical flow phantoms for use in parallel experiments involving both laser and Doppler ultrasound measurement techniques.     

Dynamic resolution selection in ultrasonic strain imaging

Ultrasonic strain imaging promises to be a valuable tool in medical diagnostics. Reliability and ease-of-use have become important considerations. These depend on selection of appropriate imaging parameters. Two tasks are undertaken here. The tradeoff between resolution and estimation precision is examined closely to establish models for the relationships with imaging parameters and data properties. These models are then applied in a system that automatically sets the imaging parameters responsive to the data quality and the required estimation precision, so as to produce more meaningful images under varying scan conditions. The new system is applied to simulation, in vitro and in vivo data for validation. It reduces the complexity of the sonographer's role in strain imaging, and produces images of reliable quality even when the level of signal decorrelation varies throughout the ultrasound data. (E-mail: jel35@eng.cam.ac.uk)     

超声影像设备质量保证用体模国产化和标准化的迄今发展

体模、试件是超声影像设备性能检测和质量保证的关键技术手段。本文描述其国产化、标准化的发展历程和现状,并为此阐释了若干重要定义,归纳了表征超声影像设备技术性能的主要参数。     

Depth selective acousto-optic flow measurement

Optical based methods for non-invasive measurement of regional blood flow tend to incorrectly assess cerebral blood flow, due to contribution of extra-cerebral tissues to the obtained signal. We demonstrate that spectral analysis of phase-coded light signals, tagged by specific ultrasound patterns, enables differentiation of flow patterns at different depths. Validation of the model is conducted by Monte Carlo simulation. In-vitro experiments demonstrate good agreement with the simulations'' results and provide a solid validation to depth discrimination ability. These results suggest that signal contamination originating from extra-cerebral tissue may be eliminated using spectral analysis of ultrasonically tagged light.OCIS codes: (170.1065) Acousto-optics, (170.4090) Modulation techniques, (280.2490) Flow diagnostics, (170.7170) Ultrasound, (170.1470) Blood or tissue constituent monitoring, (170.3660) Light propagation in tissues     

New and future developments in cerebrovascular ultrasound,magnetic resonance angiography,and related techniques

Four-dimensional (4D) analysis of atherosclerotic plaque and wall motion, the application of 4D ultrasound to the study of atherogenesis, and the incorporation of ultrasound data into flow models for simulation of cerebrovascular hemodynamics are new frontiers in diagnostic ultrasound that use computer vision and optical flow techniques to exploit the full potential of real-time imaging and Doppler studies. New approaches to improve blood vessel delineation with ultrasound include application of contrast agents, harmonic imaging, and red blood cell density imaging. An assessment of the potential clinical utility of these new developments in cerebrovascular ultrasound requires an analysis of comparable trends in magnetic resonance (MR) technology, eg, rapid advances in the fields of MR angiography, dynamic contrast-enhanced MR, and MR diffusion imaging. Likewise, the value of ultrasound techniques for the measurement of blood flow to evaluate cerebrovascular hemodynamics must be compared to related methods in magnetic resonance, such as dynamic MR inflow tracking. This article addresses several new and future developments in cerebrovascular ultrasound and discusses their relative merits in terms of ongoing research in the field of magnetic resonance angiography, imaging, and related techniques. © 1995 John Wiley & Sons, Inc.     

Validation of Endoscopic Ultrasound Measured Flow Rate in the Azygos Vein Using a Flow Phantom

Increase in flow rate within the azygos vein may be used as an indicator of the degree of liver cirrhosis. The aim of this study was to evaluate the error in measurement of flow rate using a commercial endoscopic ultrasound system, using a flow phantom that mimicked azygos vein depth, diameter and flow rate. Diameter was underestimated in all cases, with an average underestimation of 0.09 cm. Maximum velocity was overestimated, by 4 ± 4% at 50°, 11 ± 3% at 60° and 23 ± 7% at 70°. The increase in error with beam-vessel angle is consistent with the error as arising from geometric spectral broadening. Flow was underestimated by amounts up to 33%, and it is noted that the overestimation caused by geometric spectral broadening is in part compensated by underestimation of diameter. It was concluded that measurement of flow rate using a commercially available endoscopic ultrasound system is dependent on the beam-vessel angle, with errors up to 33% for typical vessel depths, diameter and beam-vessel angle. (E-mail: P.Hoskins@ed.ac.uk)     

Quantitative Contrast-Enhanced Ultrasound Comparison Between Inflammatory and Fibrotic Lesions in Patients with Crohn's Disease

The aim of this study was to determine whether there are differences in absolute blood flow between patients with Crohn's disease with inflammation or fibrosis using contrast-enhanced ultrasound. Eighteen patients with fibrotic disease and 19 patients with inflammation were examined. Video sequences of contrast data were analyzed using a pharmacokinetic model to extract the arterial input and tissue residue functions with a custom software, enabling calculation of the absolute values for mean transit time, blood volume and flow. Feasibility of the examination was 89%. The fibrosis group had lower blood volume (0.9 vs. 3.4 mL per 100 mL tissue; p = 0.001) and flow (22.6 vs. 45.3 mL/min per 100 mL tissue; p = 0.003) compared with the inflammation group. There was no significant difference in mean transit time (3.9 vs. 5.5 s). In conclusion, absolute perfusion measurement in the gastrointestinal wall using contrast-enhanced ultrasound is feasible. There seems to be reduced blood volume and blood flow in patients with fibrotic disease.     

Perfusion MR imaging: evolution from initial development to functional studies

A critical indicator of tissue viability and function is blood delivery to the capillary bed (referred to as perfusion or tissue/capillary blood flow), so the measurement of this process has been pursued by many MR scientists. Perfusion MRI is currently an effective tool to non-invasively quantify cerebral blood flow (CBF) and to easily obtain its relative change due to neural activity or other stimulus. This article describes the author's experiences in perfusion MRI over the past quarter-century, including initial development of the field, development of a flow-sensitive alternating inversion recovery (FAIR) MRI technique, development of a functional oxygen consumption MRI measurement approach, validation of the FAIR technique, characterization of perfusion changes induced by neural activity, and determination of arterial blood volume.     

彩色多普勒超声在骨肿瘤诊断中的应用价值

目的：探讨彩色多普勒超声在诊断骨肿瘤中的价值。方法：应用二维及彩色多普勒超声显像对22例恶性和27例良性骨肿瘤进行检查，观察分析病变的声像图特征、血流分布和血流动力学变化。结果：良、恶性组问血流分级有显著差异（P＜0．01），组间收缩期峰值流速（PSV）及舒张末期流速（EDV）的差异不明显（P〉0．05），阻力指数（RI）差异显著（P＜0．01）。Pearson线性相关分析显示骨肿瘤的声像图特征和血流情况与良、恶性均有良好的相关性。结论：超声对骨肿瘤病变周围软组织浸润的判断具有独特的优势，CDFI对良、恶性的鉴别诊断有一定的意义。     

New developments in the sonographic assessment of ovarian, uterine, and breast vascularity

Recent developments in ultrasound have presented new opportunities for assessing tissue vascularity and blood flow with ultrasound. These new methods include 3D imaging, power Doppler sonography, a variety of harmonic imaging techniques, ultrasound contrast agents, electronic compounding, and pulse sequencing methods that improve the signal-to-noise relationship as well as structural conspicuity. By using these technological advances, it is now possible to assess macroscopic blood flow in organs and tumors, and to assess changes in flow and vascularity that occur in response to therapeutic efforts. This review article describes and illustrates the concepts and methods used to evaluate vascularity and blood flow in tissues with ultrasound. It describes some of the potential clinical applications of these new techniques in the ovary, uterus, endometrium, adnexal vessels, and breast.     

组织谐波成像在腹部脏器的临床应用

目的 探讨组织谐波成像技术在腹部脏器的临床应用价值。方法 分别采用常规基波成像(FI)，及组织谐波成像(THI)对138例腹部脏器正常组及疾病组二维声像图及诊断检出率进行比较。结果 THI明显改善了FI状态下二维图像质量：正常腹部脏器结构及层次显示清晰，疾病组声像图特征明显，提高了检出率及鉴别诊断水平；同时，THI明显减少伪像，增加细微组织结构分辨能力，在胆囊疾病诊断中尤其有意义。结论 随着技术的不断改善，THI能为超声提供更有诊断价值的信息。     

超声多普勒检测肾动脉最低灌注压及有效灌注压的实验研究

生理学上肾动脉存在着临界关闭压，Gosling于1991年提出用超声多普勒检测肾动脉临界关闭压（本文称其为最低灌注压Pz）的公式，为反映肾动脉实际血流灌注状况，本文将平均动脉压和最低灌注压间的差值称之为有效灌注压Pe。本研究利用超声多普勒检测犬失血性休克和补液过程中肾动脉Pz、Pe的变化以验证超声多普勒检测肾动脉Pz、Pe的可信性，并对其机理、应用价值作一探讨。结果：1．随着失血量的增加，MAP的下降，Pe呈现下降趋势；随着补液的进行，血容量的增加，Pe呈现上升趋势，指标的变化符合病理生理反应；2．Pz的变化符合失血性休克过程中肾动脉的自身和全身性调节作用；3．补液后Pe的变化和尿量的变化相关良好；4．失血过程中Pe的急骤下降先于MAP的急骤下降。结论：超声多普勒检测Pz、Pe是可信的，能反映肾血流灌注状况；对临床判断肾功能、肾血流灌注情况有实用价值。     

Pulsatile flow phantom for ultrasound image-guided HIFU treatment of vascular injuries

A pulsatile flow phantom was developed for studies of ultrasound image-guided high intensity focused ultrasound (HIFU) application in transcutaneous hemostasis of injured blood vessels. The flow phantom consisted of a pulsatile pump system with instrumented excised porcine carotid artery, which was imbedded in a transparent agarose gel to model structural configuration of in vivo tissues. Heparinized porcine blood was circulated through the phantom. The artery was injured using an 18-gauge needle to model a penetrating injury in human peripheral vasculature. A HIFU transducer with the diameter of 7 cm, focal length of 6.3 cm and frequency of 3.4 MHz was used to seal the puncture. Ultrasound imaging was used to localize and target the puncture site and to monitor the HIFU treatment. Triphasic blood flows present in the human arteries were reproduced, with flow rates of 50 to 500 mL/min, pulse rates of 62 to 138 beats/min and peak pressures of 100 to 250 mm Hg. The penetrating injury of an artery was mimicked successfully in the flow phantom setting and was easily visualized both optically through the transparent gel and with power Doppler ultrasound imaging. Hemostasis was achieved in 55 +/- 31 s (n = 9) of HIFU application. Histologic observations showed that a HIFU-sealed puncture was filled with clotted blood and covered with a fibrin cap. The pulsatile flow phantom provides a controlled and repeatable environment for studies of transcutaneous image-guided HIFU application in hemostasis of a variety of blood vessel injuries.     

Doppler ultrasound diastolic flow analysis for the early identification of peripheral arterial disease.

OBJECTIVE: The viscoelastic mechanical compliance properties of the human arterial system were examined in 100 subjects with A-mode Doppler ultrasound diastolic flow analysis. This technique of diastolic flow analysis is utilized to identify early atherogenic peripheral arterial disease. The sensitivity of the commonly utilized standard traditional ultrasound pressure-grade pneumatic cuff examination will be increased when accompanied by the diastolic flow analysis technique. SETTING: Diastolic flow analysis will aid in the early identification of lower extremity vascular claudication when lumbar spinal canal stenosis and elevated cardiovascular risk factors are present. This examination may be performed in the office setting with standard A-mode Doppler ultrasound equipment along with the usual pneumatic cuff procedure. The standard ultrasound cuff examinations are based on pressure gradients to identify lower extremity arterial disease. The low level of sensitivity of this test requires arterial obstruction of at least 50% to be present before positive identification is possible. Pathological alterations of the arterial wall occur during the early stages of atherosclerotic disease, are reflected by reduced wall distensibility and may be quantified by Doppler ultrasound. SUBJECTS: Studied were a total of 100 subjects, 50 with arterial disease risk factors and 50 normal controls. All subjects were screened for aortic coarctation, myocardial infarction, tachyarrhythmia, aortic value stenosis and mitral prolapse. The risk group subjects were all smokers and had a mixed distribution of hypertension, hypercholesterolemia and hyperglycemia. The commonly utilized standard traditional ultrasound pneumatic cuff examination was negative in all subjects. Anthropometric measurements and percent body fat were also obtained. Arterial diastolic antegrade flow analysis was performed with Doppler ultrasound on each subject. RESULTS: This study demonstrated that the elevated vascular risk factor group had a mean arterial distensibility measurement of 4.4 +/- 5.0%, and the control group displayed a mean measurement of 20.0 +/- 6.0%. The 50 elevated risk factor subjects showed approximately 5 times greater arterial stiffness and were identified with significance at an F test level of (p less than .001). CONCLUSION: This arterial compliance evaluation procedure is shown to be a reliable sensitive indicator of early atherosclerotic disease prior to the development of obstructive arterial lesions.     

An arterial wall motion test phantom for the evaluation of wall motion software

Increasing cardiovascular disease has led to new ultrasound methods of assessing artery disease such as arterial wall motion measurement. To validate arterial wall motion software, we developed a mechanically-controlled wall motion test phantom with straight upper and lower agar tissue mimicking material layers that resemble an artery cross section. The wall separation, displacements and wall velocities and accelerations can be controlled within physiologically realistic levels. A user-definable displacement or one of several pre-defined displacement waveforms can be created by the user with custom-written software. The test phantom is then controlled using the defined waveform with a stepper motor controller. Accuracy assessment of the test phantom with a laser vibrometer yielded a positional accuracy of 36+/-2 microm. A typical application of the test phantom is demonstrated by assessing a tissue Doppler imaging (TDI) method for estimating the distension waveform. The TDI-based method was found to have a minimum resolvable displacement of 22.5 microm, and a measurement accuracy of +/-8% using a physiological wall motion movement with a peak displacement of 689 microm. The accuracy of the TDI method was found to decrease with decreasing wall displacement and increasing wall velocity.     

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).