Angle Of Insonation Research Articles

Assessment of intracranial collateral flow by transcranial color-coded duplex sonography using a temporal and frontal axial insonation plane.

The insonation of the posterior communicating artery (PcomA) is often hampered by the unfavorable insonation angle when the temporal acoustic bone window (TBW) is used. This problem may be ameliorated by a lateral frontal bone window (LFBW). This study evaluated the TBW and LFBW for the assessment of collateral intracranial flow conditions and aimed at defining diagnostic transcranial color-coded duplex sonography (TCCS) criteria that do not need compression maneuvers. The A1 segment of the anterior cerebral artery (ACA), the PcomA, and the P1 segment of the posterior cerebral artery (PCA) were insonated by TCCS in 40 controls and 20 patients (16 internal carotid artery [ICA] occlusions or high grade stenoses, 3 middle cerebral artery stenoses or occlusions, 1 PCA stenosis). Detection rates for the A1 ACA and P1 PCA were higher for the TBW (94%, 98%) compared to the LFBW (86%, 81%) in controls. The PcomA was identified more frequently through the LFBW (86%) compared to the TBW (80%). Through the LFBW angle, corrected flow velocity (FV) measurements were possible for the PcomA with an average correction of 6.5 degrees. In controls, in > 80% of identified PcomAs, flow was directed towards the ICA. Side to side differences were below 7% for peak systolic FVs. In the patients with ICA disease, a flow reversal in the ipsilateral A1 ACA and a FV difference of > 30% seemed feasible for diagnosis of anterior communicating artery crossflow. Criteria for PcomA crossflow were side differences of FVs in the PcomA of > or = 30% and in the P1 PCA of > or = 20%. The LFBW proved useful as a complementary insonation plane to assess intracranial crossflow conditions, especially via the PcomA. We were able to define TCCS criteria for functional relevant collateralization without the need of compression maneuvers.

Effect of Age on Cerebral Blood Flow Velocity in Patients After Aneurysmal Subarachnoid Hemorrhage

To the Editor: We read with interest the article by Torbey et al1 on effect of age on cerebral blood flow velocity in patients after aneurysmal subarachnoid hemorrhage, published in the September issue of Stroke . Using conventional transcranial Doppler ultrasonography, the authors report an unexpectedly large decrease in flow velocity in the middle cerebral artery (MCA) in patients older than 68 years in comparison to those younger than 68 years. The mean flow velocity in the MCA was found to be 42 cm/s in the former and 81 cm/s in the latter group. Thus, the difference was as much as 48%, whereas elsewhere, in other large groups of healthy subjects, the range of difference was only between 17% and 22%.2,3⇓ The fact that the authors found a higher incidence of vasospasm in the younger group cannot explain the discrepancy because such significant differences in flow velocity were found at admission, ie, before the vasospasm usually develops. The authors have addressed only superficially a fundamental question: why does subarachnoid hemorrhage affect cerebral vessels in older patients differently? The problem is even more intriguing given the fact that vasoreactivity appears not to be affected by normal aging.4,5⇓ We suspect that the decline in flow velocity in reality does not need to be as substantial as the authors state. The conventional Doppler technique they used does not allow measurement of the angle of insonation of the vessel, which is crucial in their setup of the study. In young persons the horizontal portion of the MCA projects laterally toward the temporal acoustic window, whereas in older subjects it bows ventrally, which results in a wider angle of insonation.6 No exact data on the real magnitude of this angle in normal elderly subjects have been published to date. …

Wavelet analysis of bathymetric sidescan sonar data for the classification of seafloor sediments in Hopvågen Bay - Norway

In this paper we examine the use of bathymetric sidescan sonar for automatic classification of seabed sediments. Bathymetric sidescan sonar, here implemented through a small receiver array, retains the advantage of sidescan in speed through illuminating large swaths, but also enables the data gathered to be located spatially. The spatial location allows the image intensity to be corrected for depth and insonification angle, thus improving the use of the sonar for identifying changes in seafloor sediment. In this paper we investigate automatic tools for seabed recognition, using wavelets to analyse the image of Hopvagen Bay in Norway. We use the back-propagation elimination algorithm to determine the most significant wavelet features for discrimination. We show that the features selected present good agreement with the grab sample results in the survey under study and can be used in a classifier to discriminate between different seabed sediments.

Real‐Time Strain Rate Imaging: Validation of Peak Compression and Expansion Rates by a Tissue‐Mimicking Phantom

Strain rate imaging is a new modality in echocardiography intended for analysis of left ventricular function. This modality extends ultrasonographic techniques for analysis of tissue velocities by providing information about rates of local myocardial compression and expansion. Cyclic cardiac deformation is a complex process. Precision and accuracy of real-time strain rate (rtSR) measurements have not been studied under controlled laboratory conditions. Using a cyclically compressed tissue-mimicking gelatin phantom, we compared rtSR values to corresponding strain rate values calculated off line from local tissue velocities measured by Doppler echocardiography. We tested a clinically relevant range of strain rates (0.5 - 3.5 sec(-1)) and different angles of insonation. Initial tests showed high precision (r > or = 0.973, P < 0.001), but the assessment of accuracy (bias < or = 0.559 sec(-1)) suggested a trend toward systematic underestimation of the reference values. We suspected a confounding influence of a clutter filter and repeated the tests with the filter inactive. The resulting accuracy improved tenfold (bias < or = 0.045 sec(-1)), and the systematic underestimation was no longer present. We conclude that the rtSR is precise and accurate for a range of the tested values.

Quantification of fetal power Doppler: determination of the intravascular standardization point

Background: With its sensitivity to low flow, lack of aliasing and relative angle independence, power (amplitude) Doppler ultrasound is well suited to assessment of tissue perfusion. However, the influence of machine settings, depth and other factors related to attenuation means that perfusion measurements taken from deep tissue without standardization to 100% flow are relatively meaningless. Previously published adult research has proposed a technique to estimate a true value for 100% amplitude from a cumulative power distribution across a large local vessel. This standardization value allows measurement of fractional moving vascular volume as an ultrasound index of perfusion.Methods: Fetal renal and aortic blood flow was evaluated using the power Doppler mode of the Acuson Sequoia™. Color flow information was digitally segmented to a linear 8‐bit scale and analyzed using CQ Analysis software as previously reported by our group. Using images from the fetal aorta with and without the kidney, of both segmented and unsegmented images, an attempt was made to plot the cumulative power distribution in eight fetuses (27–37 weeks' gestation). Fetal aortic amplitude information was then examined using a combination of CQ Analysis, Scion Image and Excel software. Peak amplitude was examined between different ultrasound clips in a single fetus and in 50 frames through the cardiac cycle in 10 fetuses. Spatial variation in peak aortic amplitude was examined in 50 frames from four fetuses with varying angle of insonation from 73° to 88°. Temporal variation was examined in 50 frames from a single fetus.Results: In the human fetus, there is no peak vascular value or corresponding ‘knee point’ attributable to the effects of rouleaux. In contrast, the peak aortic value is relatively constant for 100% flow, both between multiple imaging clips and throughout the cardiac cycle in the 10 fetuses. Spatial variation for the 100% flow value increased from an average coefficient of variation of 6.5% at 79° to 28% at 89°. Temporal variation was 8% over 50 frames.Conclusions: The human fetus has a reduced degree of rouleaux formation in part due to an altered form of fibrinogen and reduced concentration of plasma proteins, so the peak amplitude measurement in the center of large vessels represents true 100% flow. This finding is confirmed by the lack of cardiac cycle effects on the amplitude profile. The central value of larger blood vessels, such as the fetal aorta, if measured at an appropriate angle of insonation, may provide a relatively constant standardization value for vessels or regions at a similar depth. From these, true measurements of fractional moving vascular volume may be derived.Acknowledgements: Alec Welsh was supported by a Research Training Fellowship from RCOG/WellBeing, the BUPA Research Foundation Clinical Scientist Award 2000 and the 2001 Bernhard Baron/RCOG Travelling Scholarship.

Ultrasound contrast agents: properties, principles of action, tolerance, and artifacts.

The concept of contrast imaging was introduced to ultrasound almost 30 years ago. The development of ultrasound contrast agents (USCAs), initially slowed by technical limitations, has become more dynamic during the past decade. The ideal USCA should be non-toxic, injectable intravenously, capable of crossing the pulmonary capillary bed after a peripheral injection, and stable enough to achieve enhancement for the duration of the examination. While satisfying cost-benefit requirements, it should provide not only Doppler but also gray-scale enhancement. Already, Doppler examinations are improved by using USCAs when studying deep and small vessels, vessels with low or slow flow, or vessels with a non-optimal insonation angle. Ultrasound contrast agents also enhance detection of flow within abnormal vessels, including tumor vascularization and stenotic vessels, and provide better delineation of ischemic areas. Research is focusing on the development of specific contrast imaging sequences that allow detection of tissue enhancement similar to that obtained with CT or MRI. These sequences take advantage of the nonlinear behavior of the microbubbles within the ultrasound field, bringing real-time perfusion imaging for liver, kidney, and the myocardium into reach. New objectives include targeted agents that could further widen USCA applications to specific delivery of active drugs such as anticoagulants or cytotoxic compounds. The combination of new generations of USCAs and new ultrasound image sequences appears to be very promising and currently represents a significant part of ultrasound research.

The importance of Doppler angle of insonation on differentiation between 50-69% and 70-99% carotid artery stenosis.

to investigate the importance of Doppler angle differentiating between 50-69% and >/=70% internal carotid artery (ICA) stenosis. fifty-one patients with a previous diagnosis of 50-69% ICA stenosis (n =53) were re-evaluated by duplex scanning. Spectral Doppler velocity waveforms were obtained from common carotid (CCA), ICA and external (ECA) carotid arteries with the same Doppler angle of insonation as used at the initial duplex scanning, followed by repeated measurements with a fixed 60 degrees angle of insonation. the peak systolic velocity (PSV) in the ICA was 181+/-55 cm/s (mean+/-SD) at the second duplex scanning when the same angle of insonation (mean 46 degrees +/-9) was used as during the initial investigation. When the examination was done with a 60 degrees angle of insonation, PSV ICA was 261+/-96 cm/s (mean+/-SD). In fifteen arteries the estimated degree of ICA stenosis changed from 50-69% to 70-99% due to the application of a fixed Doppler angle of insonation at 60 degrees. the Doppler angle of insonation has a significant effect on spectral Doppler velocity measurements. It is crucial that duplex criteria are standardised with a fixed angle of insonation and that this angle is consistently used during velocity estimations.

The use of beam angulation to overcome anisotropy when viewing human tendon with high frequency linear array ultrasound.

Anisotropy is the property of tendons, nerves and muscles to vary in their ultrasound appearance depending on the angle of insonation of the incident ultrasound beam. Loss of reflectivity in tendons may also denote underlying disease. We describe beam angulation, a simple technique available with most modern ultrasound machines, which allows the operator to overcome the potential pitfall of anisotropy in ultrasound assessment of peripheral tendons.

Which Parameter Measures the Effectiveness of Volume Preload in Pregnant Patients?

Osaka University Medical SchoolSuita, Osaka, Japan.ueyama@hp-op.med.osaka-u.ac.jpIn Reply:—We thank Dr. Marcus for the interest in our work and the comments. In parturients with normal uteroplacental circulation, uterine blood flow is the major determinant of oxygen transport to the fetus. The increase in uterine blood flow after colloid preload suggested by Dr. Marcus is interesting. Our results suggested that colloid preloading resulted in marked increases in maternal cardiac output without significant change in blood pressure. Therefore, the increase in uterine blood flow may be associated with an increase in maternal cardiac output.Doppler ultrasonography is the most commonly used method to measure uterine blood flow in humans. The velocity of the blood flow is one of the representative parameters measured with Doppler ultrasonography. However, the reliability of the measurements is controversial because shape of the waveform is affected by many factors, such as maternal cardiac output, elasticity of the vessel wall, outflow impedance, and blood viscosity. Calculation of blood flow necessitates precise determination of mean velocity, angle of insonation, and vessel diameter. Although angle of the insonation and blood velocity are determined correctly, accurate measurement of small-vessel diameters, such as the diameter of a uterine artery, is difficult. It is also not clear whether the blood flow reflects the functional placental perfusion because some portion of blood flow is shunted to the myometrium. Therefore, extrapolation of measurements from the Doppler ultrasonographic method must be done with caution.As Dr. Marcus pointed out, an understanding of the uteroplacental blood flow is essential in obstetric anesthesia practice. However, the goal of our anesthetic management is to maintain fetal oxygenation, not uterine artery blood flow. We think that, in the future, fetal oxygenation monitoring would show the effect of preloading on fetal oxygenation.

Modeling and analysis of ultrasound backscattering by spherical aggregates and rouleaux of red blood cells

The present study concerns the modeling and analysis of ultrasound backscattering by red blood cell (RBC) aggregates, which under pathological conditions play a significant role in the rheology of blood within human vessels. A theoretical model based on the convolution between a tissue matrix and a point spread function, representing, respectively, the RBC aggregates and the characteristics of the ultrasound system, was used to examine the influence of the scatterer shape and size on the backscattered power. Both scatterers in the form of clumps of RBC aggregates and rouleaux were modeled. For all simulations, the hematocrit was kept constant at 10%, the ultrasound frequency was 10 MHz, the insonification angle was varied from 0 to 90 degrees , and the scatterer size (diameter for clumps and length for rouleaux) ranged from 4 mum to 120 mum. Under Rayleigh scattering by assuming a Poisson distribution of scatterers in space, the ultrasound backscattered power increased linearly with the particle volume. For non-Rayleigh scatterers, the intensity of the echoes diminished as the scatterer volume increased, with the exception of rouleaux at an angle of 90 degrees . As expected, the backscattered power was angularly dependent for anisotropic particles (rouleaux). The ultrasound backscattered power did not always increase with the size of the aggregates, especially when they were no longer Rayleigh scatterers. In the case of rouleaux, the anisotropy of the backscattered power is emphasized in the non-Rayleigh region.

Volumetric flow in the umbilical artery: Normative data

Objective Provide normative data for the volumetric blood flow (cc/min and cc/min/kg) in the umbilical artery. Methods Flow was determined from an umbilical artery in 252 normal obstetrical patients from 18–40 weeks' gestation utilizing pulsed Doppler and color flow Doppler with an angle of insonation of 30–60°. Simultaneous velocimetry studies (S/D ratio, resistance and pulsatility indices), fetal biometry, and an anatomic survey were obtained to further define the normal population. Results There was a steady increase in the flow (cc/min) in the umbilical artery as pregnancy progressed. Flow/kg showed a steady decline as fetal weight increased. Umbilical artery diameter increased until reaching a plateau at 32–34 weeks. Velocimetric results were consistent with known data. Conclusions Volumetric blood flow in the umbilical artery can be determined with relative ease and normative data from 18–40 weeks is presented for the first time. J. Matern.-Fetal Med. 9:224–228, 2000. © 2000 Wiley-Liss, Inc.

Intrinsic spectral broadening (ISB) in ultrasound Doppler as a combination of transit time and local geometrical broadening

Doppler signals collected with a focused transducer are known to be affected by the so-called intrinsic spectral broadening (ISB). This article aims to point out how ISB is, in general, related to both the limited lateral extent of a focused beam (leading to a finite transit time), and the presence of several local insonation angles around the beam axis, due to focusing and diffraction effects (local geometrical broadening). The influence of these two elementary spectral contributions on the whole ISB is shown by considering the Doppler signal as simultaneously modulated in amplitude and frequency, and applying well-known relationships employed in the communication field. Such an analysis reveals that transit time and local geometrical broadening are two different phenomena, whose simultaneous knowledge is necessary for correctly evaluating the overall ISB. Finally, thanks to a novel technique for separately measuring transit time and local geometrical broadening effects on transducers with markedly different focusing properties, more than 1000 experimental acquisitions show how a proper combination of such measured contributions gives an accurate ISB estimation, confirming the theoretical expectations.

Benefit of echocontrast-enhanced transcranial color-coded duplex ultrasound in the assessment of intracranial collateral pathways.

Although clinically important, proper assessment of intracranial arterial collateral pathways by transcranial color-coded duplex sonography (TCCD) in patients with internal carotid artery (ICA) high-grade stenosis or occlusion is occasionally made difficult by an insufficient temporal bone window, an unfavorable insonation angle, or low flow velocity or volume. In these cases, echocontrast could be helpful to increase the diagnostic confidence or to make the diagnosis at all. We investigated 50 temporal windows of 44 patients with ipsilateral high-grade (>/=70%) ICA stenosis or occlusion and insufficient native transtemporal insonation conditions before and after the application of the echo enhancer Levovist with an infusion pump. Compared with the precontrast scans, echocontrast allowed for more segments to be evaluated by pulsed Doppler sonography (P<0. 0001) and for longer lumen segments to be displayed on color mode (P<0.0001). Also, collateral flow via the anterior and posterior communicating artery could be demonstrated in 25 and 32 scans, respectively, compared with only 1 demonstration of each collateral pathway before the application of contrast medium (both P<0.0001). Similarly, with the help of contrast medium, flow velocity in the middle cerebral artery could be measured in 45 cases compared with only 26 cases before contrast was applied (P<0.0001). In patients with poor precontrast visualization of intracranial arteries, echocontrast-enhanced TCCD is very helpful in the assessment of intracranial collateral pathways recruited downstream to ICA stenoses and occlusions.

Relative Ultrasonographic Echogenicity of Standard, Dimpled, and Polymeric-coated Needles

To use quantitative ultrasonographic measurements to compare the effect of a polymeric coating designed to increase needle echogenicity to commercially available needles. Commercially available standard smooth and dimpled echogenic tip 21-gauge needles established reference levels of echogenicity in gelatin-based and turkey breast phantoms. Examples of both types of needles were coated with a thin polymeric film that utilizes entrapped microbubbles of air on its surface to increase echogenicity. Samples of each type in both coated and noncoated versions were placed in phantoms in matched positions and imaged with clinical ultrasound machines. Similar numbers of each category were evaluated at various angles of insonation for a total of 109 images. Similar numbers of each category were imaged at 5-minute intervals for up to 38 minutes for a total of 226 images. Images were recorded, digitized, and evaluated for relative echo strength in arbitrary echogenic brightness units. Coating increased peak echogenicity over the entire needle to a level that closely approximates the peak echogenicity of dimpled needle tips (means: dimpled = 834, coated smooth = 803, coated dimpled = 823; P = .54). Smooth is lower than this group at 468 (P = .0001). Representative area echogenicity increased with coating or dimpling (smooth = 377 vs coated smooth = 778, coated dimpled = 690, dimpled = 775; P = .0001). Coating increased peak values 74% and area values 95% compared to smooth. Decreased angles of insonation moderately reduced echogenicity on coated smooth, coated dimpled, and dimpled, while it decreased to below good visibility threshold on standard smooth needles. The echogenicity of the coated needles fades in saline with time (1%/min). Objective measurements show that this coating significantly increases echogenicity of entire needles to match that obtained with a dimpled tip.

Intra-operative measurement of cortical arterial flow volumes in posterior circulation using Doppler sonography

Little has been reported on the flow volume of cortical arteries in the posterior circulation. During craniotomy in 28 patients, we measured the flow velocity of the arteries using microvascular Doppler sonography and recorded their arterial radii and the insonation angle. The flow velocities and radii were 25.7 cm sec–1 and 0.11 cm for the posterior cerebral artery (PCA), 19.5 cm sec–1 and 0.07 cm for the superior cerebellar artery (SCA), 19.6 cm sec–1 and 0.04 cm for the anterior inferior cerebellar artery (AICA), 14.9 cm sec–1 and 0.05 cm for the posterior inferior cerebellar artery (PICA), 28.3 cm sec–1 and 0.18 cm for the basilar artery, and 18.5 cm sec–1 and 0.16 cm for the vertebral artery, respectively. Since the flow velocities of these arteries were confined in a narrow range compared to the cross-sectional areas, the latter was considered to be the primary determinant for flow volume in these arteries. Based on certain assumptions, we estimated the flow volume of the PCA, SCA, AICA and ICA to be 60, 20, 10 and 10 ml min–1, respectively, which could be regarded as the current reference values for the arterial flow volumes. [Neurol Res 2000; 22: 194-196]

Doppler flow measurement using surface integration of velocity vectors (Sivv): in vitro validation

Blood flow measurement using an improved surface integration of velocity vectors (SIVV) technique was tested in in vitro phantoms. SIVV was compared with true flow (12–116 mL/s) in a steady-state model using two angles of insonation (45° and 60°) and two vessel sizes (internal diameter = 11 and 19 mm). Repeatability of the method was tested at various flow rates for each angle of insonation and vessel. In a univentricular pulsatile model, SIVV flow measured at the mitral inlet was compared to true flow (29–61 mL/s). Correlation was excellent for the 19-mm vessel (r 2= 0.99). There was a systematic bias but close limits of agreement (mean ± 2 SD = −24.1% ± 7.6% at 45 °; +16.4% ± 11.0% at 60 °). Using the 11-mm vessel, a quadratic relationship was demonstrated between between SIVV and true flow (r 2 = 0.98–0.99), regardless of the angle of insonation. In the pulsatile system, good agreement and correlation were shown (r 2 = 0.94, mean ± 2 SD = −4.7 ± 10.1%). The coefficients of variation for repeated SIVV measurements ranged from 0.9% to 10.3%. This method demonstrates precision and repeatability, and is potentially useful for clinical measurements.

Volumetric flow in the umbilical artery: normative data.

Provide normative data for the volumetric blood flow (cc/min and cc/min/kg) in the umbilical artery. Flow was determined from an umbilical artery in 252 normal obstetrical patients from 18-40 weeks' gestation utilizing pulsed Doppler and color flow Doppler with an angle of insonation of 30-60 degrees. Simultaneous velocimetry studies (S/D ratio, resistance and pulsatility indices), fetal biometry, and an anatomic survey were obtained to further define the normal population. There was a steady increase in the flow (cc/min) in the umbilical artery as pregnancy progressed. Flow/kg showed a steady decline as fetal weight increased. Umbilical artery diameter increased until reaching a plateau at 32-34 weeks. Velocimetric results were consistent with known data. Volumetric blood flow in the umbilical artery can be determined with relative ease and normative data from 18-40 weeks is presented for the first time.

Ultraschallkontrastmittel - Bedeutung für die neurosonologische Diagnostik

Transcranial colour-coded duplex ultrasound is frequently hampered by an insufficient temporal or foraminal window (in our experience this makes up for approximately 20 % of the cerebrovascular patients). Correspondingly, extracranial colour-coded duplex ultrasound has its limitations by plaque calcification and shadowing of the ultrasound beam. Weak Doppler signals due to a large insonation angle or low flow volume are another problem for both techniques. These limitations led to the development of echocontrast agents which were able to survive pulmonary and capillary transit and improved the echogenecity of the flowing blood. During Doppler sonography, these echocontrast agents enhance the signal by up to 30 dB. Echocontrast increases the success rate of ultrasound examinations, shortens the time needed for the examination, and allows for visualisation of more vessels and longer vessel segments. Still under investigation are brain perfusion mapping, harmonic imaging, a technique based on harmonics, and stimulated emission based on ultrasound scattering by bursting echocontrast microbubbles.

Quantitative Doppler measures in coiled vessels: investigation on excised umbilical veins

Quantitative assessment of umbilical venous blood velocity with Doppler ultrasound (US) must cope with the coiled structure of the vein inside the cord. Both an experimental and a theoretical approach showed remarkable variations in the insonation angle when the probe was moved along the vein, provided the inclination between the Doppler probe and the cord was kept constant. Inaccurate signal processing, stochastic variability and flow disturbances could, however, mask the influence of the geometry. The above hypotheses were assessed by investigating five cords in vitro a few hours after delivery from normal pregnancies at term. The Doppler signal was sampled at different sites along each cord and the mean Doppler shift estimated by FFT spectral analysis, both directly and through the noise rejection D’Alessio’s algorithm, which proved effective in improving the Doppler shift estimate in condition of low signal-to–noise ratio (SNR).

Sonographic evaluation of the posterior cruciate ligament in amputated specimens and normal subjects.

The purpose of this study was to define the sonographic appearance and echogenicity of the normal posterior cruciate ligament. We examined the posterior cruciate ligament of five amputated specimens and five normal subjects using a 10 MHz linear array transducer. One K-wire was inserted into the substance of the posterior cruciate ligament of the amputated knee specimens to verify the location of the ligament on the sonogram. Various angles of insonation were used to examine the echogenicity of the posterior cruciate ligament. The results showed that the in situ posterior cruciate ligament appeared as a hypoechoic band relative to the surrounding tissue on sonograms, but it appeared hyperechoic when it was isolated and immersed in a water bath. The specific spatial orientation of the posterior cruciate ligament and anisotropy phenomenon contributed to the hypoechogenicity of the posterior cruciate ligament in situ on sonogram.