Low-velocity Signals Research Articles

Compound Doppler ultrasound signal simulation for pulsatile carotid arterieswithastenosis.

The simulated Doppler blood flow signals are widely used to assess the performance of the clutter filters for removing wall components while reserving low-velocity signals scattered from physiological blood flow approaching the inner vessel-wall injured by a stenosed lesion. By simultaneously taking into account the natural attributes of the Doppler equipment, blood flow as well as vessel wall of pulsatile carotid arteries with a stenosis, a computer simulation method is presented to produce the compound Doppler ultrasound blood flow signals. The in-phase and quadrature (I/Q) axial as well as radial blood flow signals are simulated by superposing a series of cosine functions regulated by the spectrograms estimated from the axial and radial velocity profiles firstly obtained through the solution of the incompressible Navier-Stokes equations, respectively. Meanwhile, the I/Q Doppler signals echoed from pulsatile near (anterior) and far (posterior) walls are reproduced based on their radial movements during a cardiac cycle. Ultimately, those confirmed quadrature signals are summed to generate the compound Doppler signals including the contribution from both blood flow and stenosed vessel-wall. The compound Doppler ultrasound signals echoed from both axial and radial blood flows as well as vessel walls with obstruction grades of 0% (normal arteries), 10% and 25% are simulated respectively. The real signals from the left carotid artery with an approximately 10% stenosis degree are also collected for further assessing the believability of simulated versions. The simulated and clinical tests demonstrate that the proposed computer simulation method can produce compound Doppler signals with confirmed qualitative and quantitative characteristics resembled with the clinical versions, which could be used as an theoretical data source for evaluating the performance of the signal separation between pulsatile blood flows and vessel walls with mild stenosed-lesions.

Inapplicability of FMBV to VOCAL indices and the amplitude origin of power Doppler

We welcomed the Correspondence from Soares et al.1 regarding our thoughts2 on the inapplicability of the fractional moving blood volume (FMBV) concept to Virtual Organ Computer-aided AnaLysis (VOCAL) measurements. However, we believe there to be three flaws in their argument: 1) their opening sentence is slightly misleading regarding the results and conclusions of our paper; 2) a comparison between the methods of the two studies1, 2 indicates multiple differences in fixed power Doppler (PD) settings, and 3) there appear to be fundamental differences between our and their understanding of the physics of PD. Our cited paper concluded that three-dimensional (3D) FMBV using the proprietary software known as VOCAL is technically not achievable2. This is most likely to be a reflection of the fundamental properties of this particular software. We do not believe, and indeed have never claimed, that ‘fractional moving blood volume (FMBV) cannot be applied to three-dimensional power Doppler (3DPD)’. In fact, our method for generating 3D-FMBV from raw PD ultrasound signals was presented at the recent ISUOG world congress in Copenhagen3, 4. The work that is put forward to disprove our findings used different settings for frequency, line density, ensemble, smooth and balance, which may account for the variation in VOCAL index values1, 2. Whilst the underlying impact of these settings upon VOCAL indices is unknown, we would have expected Soares et al. to have used standardized settings as similar as possible to our own, in order to make appropriate comparisons. Most importantly, it appears that the authors fail to understand that PD is based upon amplitude or energy of ultrasound scattering rather than velocity5. Their Correspondence is based upon presumptions regarding Doppler shift and velocity, when it is well-established that PD is based upon amplitude. Whilst the authors are correct in stating that low pulse repetition frequencies (PRFs) ‘increase the sensitivity to detect low blood velocity’, they are incorrect in describing PD in relation to velocity of blood flow. PD is an amplitude-based technique. It quantifies all moving particles (blood) on the basis of signal strength, regardless of velocity. Doppler signals whose frequency is higher than the Nyquist limit will be aliased in spectral Doppler, but the power of the signal will not be affected by aliasing and so the PD measure should not be changed. Therefore, the assertion that high PRFs are required is irrelevant to PD, and indeed lower PRFs may at times be needed to interrogate deeper tissues. If anything, PD may be influenced by velocity at the lower rather than the higher end of the velocity range. This is because there needs to be a minimum Doppler shift detected by the transducer in order for a signal to be present that has measurable amplitude. The consequence of this is that at low flow velocities, the influence of the wall motion filter (WMF) may effectively ‘filter out’ some of the low velocity signal, which therefore cannot be measured. The authors miss this point when they describe emerging techniques to evaluate systolic and diastolic vascularity using spatiotemporal image correlation (STIC), which they erroneously describe as being ‘promising techniques to standardize 3DPD quantification’. When STIC is used to evaluate tissue vascularity it is able to produce 3D volumes from different phases of the cardiac cycle. The ratios of indices derived from volumes representative of systole and diastole may then be representative of 3D tissue resistance, as the WMF may result in more signal being filtered out in diastole than in systole6. This is the basis of novel volumetric indices such as the volumetric pulsatility index. It must be noted that these are indices that are assumed to represent impedance and they in no way act as standardization measures for 3DPD. In contrast, the FMBV technique achieves true internal standardization for vascular volume. Publication of Correspondence that erroneously applies velocity-based principles to PD imaging may mislead less experienced and emerging research groups. It is unfortunate that the derivation of indices such as those from VOCAL and their relationship to ultrasound physics are not made more explicit and readily available by the manufacturer. A. W. Welsh*†‡, S. L. Collins§¶, G. N. Stevenson** and R. Gill† †School of Women's and Children's Health, University of New South Wales, Randwick, NSW, Australia; ‡Department of Maternal-Fetal Medicine, Royal Hospital for Women, Locked Bag 2000, Barker Street, Randwick, NSW 2031, Australia; §The Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, UK; ¶The Fetal Medicine Unit, John Radcliffe Hospital, Oxford, UK; **Institute of Biomedical Engineering, Department of Engineering Science, Oxford University, Oxford, UK *Correspondence. (e-mail: [email protected])

The Origin and Clinical Significance of the Signal Opposite to the Mitral E-Wave: A Simple and Novel Indicator of Left Ventricular Filling Pressure

We noted a low-velocity signal opposite to the early diastolic transmitral flow (E) by pulsed Doppler echocardiography. The purpose of this study was to examine the origin and significance of this signal. The background of the signal remains uncertain. We studied 59 adult patients (34 men and 25 women; mean age, 58.9 [20.2] years) without mitral valve heart disease. Mitral E-wave velocity and the signal (EW) opposite the E-wave were measured by pulsed Doppler echocardiography. Early diastolic mitral valve ring motion velocity (Ea) was measured by pulsed tissue Doppler echocardiography. Pulmonary capillary wedge pressure (PCWP) was measured by a Swan-Ganz catheter in 34 of the 59 patients. A blue signal was observed during early diastole from the mitral valve ring to the mitral orifice areas by color tissue Doppler echocardiography. The velocity profile method revealed the same direction and time between peak Ea and EW. Peak EW positively correlated with Ea (r = 0.67, P < 0.01). There were significant positive correlations between mean PCWP and E/Ea (r = 0.61, P < 0.01) and E/EW (r = 0.59, P < 0.01). E/EW was significantly greater in patients with PCWP > 12 mmHg than in patients with PCWP ≤ 12 mmHg (5.6 [1.3] cm/s vs. 4.3 [0.9] cm/s, P < 0.01). EW may be related to mitral valve ring motion, and the E/EW ratio may be a noninvasive simple parameter for assessing left ventricular filling pressure.

Impact of wall filter selection on the detection of vasomotor changes in the brachial artery: a pilot study

During Doppler ultrasound assessment of blood flow, a wall filter is used to reduce or eliminate high-amplitude, low-velocity signals from the vessel wall and the surrounding tissue. This study investigated the impact of a range of wall filters (22 Hz, 75 Hz, 128 Hz, and 252 Hz) on the accuracy of forearm blood flow monitoring during the sympathoexcitatory application of lower body negative pressure, when peripheral blood flow may decrease substantially. The 252 Hz filter eliminated diastolic flow in 4 of 10 participants. In the remaining participants, the 252 Hz filter minimized the sensitivity of the pulsatility index. The interpretation of physiological responses could ultimately be compromised by using filters beyond 128 Hz.

Knock Signals in Ischemic Stroke

To the Editor: I have described a new Transcranial doppler ultrasonography finding “small vessel knock (SVK)” and have proposed that this is an obstructive arterial signal.1,2 SVK is an asymmetrical high-intensity low-velocity signal found at the baseline occurring at aortic valve opening and closure with the signals moving in opposite directions. SVK has a characteristic appearance on single-gated and M-mode spectra and can be distinguished from wall movement, which is symmetrical.3 In the February edition of Stroke , Chung et al4 report the finding of an asymmetrical SVK-like intraluminal signal in vitro, at the site of obstruction, in both silastic and glass tubing. They found that the intensity of this signal increased as the concentration of ultrasound scatterers in the lumen increased. This shows that asymmetrical SVK-like signals are intraluminal obstructive ultrasound signals. Symmetrical “knock signals” were also found because of wall movement, and these increased in intensity toward the site of obstruction. The authors stated that the lumen diameter …

Photodissociation of Propargyl Chloride at 193 nm

The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C3H3 radicals were performed, along with measurements of the Cl + C3H3 and HCl + C3H2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2P3/2) and Cl (2P1/2) (hereafter Cl) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 +/- 0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl+ mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the low-recoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C3+ ions in the mass spectrometer.

Doppler mirror image artifacts mimicking mitral regurgitation in patients with mechanical bileaflet mitral valve prostheses.

To characterize the origin and mechanisms of generation of Doppler mirror images in the left atrium observed in patients with mechanical bileaflet mitral valve prosthesis. We hypothesized that these systolic colour Doppler images are artifactual and generated by reflection of the left ventricular outflow tract flow at the leaflet of the mitral valve prosthesis. Fifty patients with mechanical bileaflet mitral valves were prospectively examined by means of transthoracic Doppler-echocardiography. From different apical views, the left atrium was carefully interrogated for systolic colour flow signals, which were further analysed by pulsed wave Doppler. In all patients, a systolic colour Doppler signal was detected in the left atrium. Pulsed wave Doppler analysis revealed a low velocity signal (= mirror image) corresponding to the shape and duration of the left ventricular outflow tract signal. The peak velocities of these mirror images, however, were consistently lower than the velocities obtained from the left ventricular outflow tract. In addition, if paravalvular mitral valve leakage was present, a high velocity signal identical to the duration of mitral regurgitation time was detected outside the ring of the prosthesis. Mirror image artifacts mimicking mitral regurgitation occur in patients with mechanical mitral valves prosthesis. As mirror image artifacts can be specifically identified by analysis of shape. velocity, and duration of pulsed wave Doppler spectra, their identification will help to avoid misinterpretation of both spectral and colour Doppler signals in patients with prosthetic mitral valves.

Accurate non-electric blasting offers odd-ball time delays : Chironis, N P Coal AgeV92, N4, April 1987, P34–36

When Amax found it must blast close to community buildings it went to controlled non-electric initiation to achieve complex patterns of timed delay shots. Instead of a safety fuse or detonating cord, some non-electric systems on the market use a hollow plastic tubing that contains an inner coating of reactive material that acts as the propagating media for a flaming gas front. One such system, for example, involves an explosive shock wave that travels through the tube at 6,500 fps to initiate non-electric detonators. But such a shock wave traveling at such high speeds was not appropriate for use as precise delay detonators. The new non-electric system at the Ayrshire mine employs a propagating rate of a low energy deflagration front traveling along the length of tubing called a transmission line. Manufactured by Ensign-Bickford Co., and called LVST Line for (for Low Velocity Signal Transmission Line), the technique initiates a signal transmission at a precise rate of 2,500 fps, or even at a slower rate, depending on the internal formulation used in the transmission line, triggering blasts from hole to hole with desired delay intervals.

Vertical Seismic Profiling--Processing and Analysis Case Study: ABSTRACT

Vertical seismic profiles require careful data collection and processing because of borehole noise and the necessity of separating upgoing and downgoing waves by apparent velocity. Major problems associated with these VSP data are tube wave noise and insufficient depth sampling. Optimum processing of these VSP data permits analysis and tracking of the compressional wave field as it propagates at depth. The aliased tube wave noise is effectively attenuated by suitable f-k filtering at some expense of signal bandwidth. Subsequently, upgoing and downgoing waves are separated and enhanced, allowing identification of primary reflections, multiples, and borehole artifacts. VSP processing results show good correlation of nearby CDP data. Limitations of VSP processing indicate the need for improved data-acquisition techniques. Increasing the source-borehole offset has been shown to attenuate borehole noise, but if interfering low-velocity signals persist, it is necessary to sample finely in depth to insure maximum signal bandwidth and high-frequency resolution after processing. End_of_Article - Last_Page 919------------