SummaryBackgroundWhether surgery is beneficial for patients with asymptomatic carotid stenosis is controversial. Better methods of identifying patients who are likely to develop stroke would improve the risk–benefit ratio for carotid endarterectomy. We aimed to investigate whether detection of asymptomatic embolic signals by use of transcranial doppler (TCD) could predict stroke risk in patients with asymptomatic carotid stenosis.MethodsThe Asymptomatic Carotid Emboli Study (ACES) was a prospective observational study in patients with asymptomatic carotid stenosis of at least 70% from 26 centres worldwide. To detect the presence of embolic signals, patients had two 1 h TCD recordings from the ipsilateral middle cerebral artery at baseline and one 1 h recording at 6, 12, and 18 months. Patients were followed up for 2 years. The primary endpoint was ipsilateral stroke and transient ischaemic attack. All recordings were analysed centrally by investigators masked to patient identity.Findings482 patients were recruited, of whom 467 had evaluable recordings. Embolic signals were present in 77 of 467 patients at baseline. The hazard ratio for the risk of ipsilateral stroke and transient ischaemic attack from baseline to 2 years in patients with embolic signals compared with those without was 2·54 (95% CI 1·20–5·36; p=0·015). For ipsilateral stroke alone, the hazard ratio was 5·57 (1·61–19·32; p=0·007). The absolute annual risk of ipsilateral stroke or transient ischaemic attack between baseline and 2 years was 7·13% in patients with embolic signals and 3·04% in those without, and for ipsilateral stroke was 3·62% in patients with embolic signals and 0·70% in those without. The hazard ratio for the risk of ipsilateral stroke and transient ischaemic attack for patients who had embolic signals on the recording preceding the next 6-month follow-up compared with those who did not was 2·63 (95% CI 1·01–6·88; p=0·049), and for ipsilateral stroke alone the hazard ratio was 6·37 (1·59–25·57; p=0·009). Controlling for antiplatelet therapy, degree of stenosis, and other risk factors did not alter the results.InterpretationDetection of asymptomatic embolisation on TCD can be used to identify patients with asymptomatic carotid stenosis who are at a higher risk of stroke and transient ischaemic attack, and also those with a low absolute stroke risk. Assessment of the presence of embolic signals on TCD might be useful in the selection of patients with asymptomatic carotid stenosis who are likely to benefit from endarterectomy.FundingBritish Heart Foundation.

Plaque morphology assessed using a simple, and clinically applicable, visual rating scale predicts ipsilateral stroke risk in ACS. The combination of ES detection and plaque morphology allows a greater prediction than either measure alone and identifies a high-risk group with an annual stroke risk of 8%, and a low-risk group with a risk of <1% per annum. This risk stratification may prove useful in the selection of patients with ACS for endarterectomy.

Results are presented from an acoustic attenuation spectroscopy study of suspensions of irregularly shaped sediment particles and of nominally spherical lead-glass beads. The measured spectra cover a wide frequency band of 1–100 MHz. It is shown that the spectra can be brought into close agreement with the rigid movable sphere model using two equivalent sphere size parameters. One parameter is the diameter dG of an equal cross-sectional area sphere, and is used to scale the frequency to obtain the nondimensional size/frequency parameter ka. The other parameter is the diameter dp of an equal volume sphere, and is used to scale the particle volume to obtain the particle number density N. It was observed that for the irregular particles the attenuation for ka&gt;1 is enhanced with respect to the sphere case. The observed enhancement factors are considerable: up to 1.6 for natural sand particles and 1.8 for the most irregular particles studied (ground quartz). In terms of the two-parameter model the enhancement factor is equal to a shape parameter b0=(dG/dp)3 and can indeed be explained as a shape effect. The implications of this result for the acoustic detection of suspended sediments in aqueous environments are discussed.

Measured and theoretical total cross sections for aqueous suspensions of lead glass and polystyrene beads are presented. Attenuation is measured from 1 to 100 MHz in a recirculating suspension circuit using a swept-frequency system and broadband transducer pairs. The theoretical calculations employ the phase shift formalism and the coherent removal of a rigid scatterer background. Good agreement between theory and experiment is obtained for both types of particle, and departures from the rigid sphere cross section are due to resonance scattering. The resonance features in the glass bead cross sections are dominated by broad Rayleigh wave resonances, with frequencies close to those given by the in vacuo free-body resonance condition, and represent departures from the rigid sphere cross section of, at most, 25%. In contrast, the polystyrene bead cross sections are dominated by narrow resonance features with maximum amplitudes up to five times greater than the geometric scattering cross section. It is shown that these resonances, which we call giant resonances, occur at frequencies given by an immersed free-body resonance condition that is derived by assuming the existence of wave trapping in the fluid at the surface of the sphere. This condition yields frequencies that are wholly real, consistent with the observed narrow resonance widths, and leads to an approximate expression for the resonance amplitudes that is in good agreement with the exact calculations. The meridional wave phase speeds are consistent in the appropriate limit with Stonely waves. The giant resonances cease to exist if the meridional wave phase speed approaches the speed of sound in the ambient fluid.

daily TCD investigation in all patients undergoing CEA seems an effective strategy for the presymptomatic detection of HS.