Background: Analysis of microembolic signals (MES) suggests a change of flow direction (CFD). The aim of the present study was to relate MES direction in an amplitude plot, based on the radiofrequent (RF) signal, to the vascular anatomy as seen with transcranial color-coded duplex (TCCD). Methods: In 5 patients undergoing heart valve surgery or aortic arch replacement, preoperatively TCCD of the distal part of the internal carotid artery and the middle and anterior cerebral arteries on the right side was performed to determine potential depths of changes in flow direction. Peroperatively, a transcranial pulsed Doppler (TCD) monitoring probe was fixed over the right temporal bone. A customized RF-based system, connected to the TCD device, captured and stored the MES. Off-line, the color-coded amplitude of the clutter-filtered RF signals was plotted as a function of time (sample interval 0.17 ms) and depth (sample interval 0.05 mm). Results: A total of 313 MES were recorded in 4 patients with 66 MES (21%) showing a CFD. All MES with CFD could be assigned to maximally three different depth values, six out of eight CFD depth values as seen with the RF analysis were within 1 mm from a turn in flow direction as estimated with TCCD. Conclusions: A CFD of MES occurred at a very limited number of depths and corresponded mostly with the intracranial vascular anatomy, namely a turn of the flow direction in the intracranial vessels as observed with TCCD.

1.
Ackerstaff RGA, Moons KGM, van de Vlasakker CJW, Moll FL, Vermeulen FEE, Algra A, Spencer MP: Association of intraoperative transcranial Doppler monitoring variables with stroke from carotid endarterectomy. Stroke 2000;31:1817–1823.
2.
Naylor AR, Hayes PD, Allroggen H, Lennard N, Gaunt ME, Thompson MM, London NJM, Bell PRF: Reducing the risk of carotid surgery: A 7-year audit of the role of monitoring and quality control assessment. J Vasc Surg 2000;32:750–759.
3.
Mess WH, Hennerici MG: High Intensity Transient Signals; in Hennerici M, Meairs S (eds): Cerebrovascular Ultrasound; Theory, Practice and Future Developments. Cambridge, Cambridge University Press, 2001, pp 297–316.
4.
Furui E, Hanzawa K, Ohzeki H, Nakajima T, Fukuhara N, Takamori M: ‘Tail sign’ associated with microembolic signals. Stroke 1999;30:863–866.
5.
Furui E, Hanzawa K, Nakajima T, Fukuhara N, Komai K, Yamada M: In vitro evaluation of the mechanism for ‘tail signs’ associated with microembolic signals (abstract). Cerebrovasc Dis 2000;10(suppl 1):2.
6.
Moehring MA, Spencer MP: Power M-mode Doppler (PMD) for observing cerebral blood flow and tracking emboli. Ultrasound Med Biol 2002;28:49–57.
7.
Mess WH, Willigers JM, Ledoux LAF, Ackerstaff RGA, Hoeks APG: Microembolic signal description: A reappraisal based on a customized digital postprocessing system. Ultrasound Med Biol 2002;28:1447–1455.
8.
Uhlmann F, Schulte-Mattler WJ, Georgiadis D: Postembolic spectral patterns of microembolic signals (abstract). Cerebrovasc Dis 2000;10(suppl 1):3.
9.
Smith JL, Evans DH, Naylor AR: Analysis of the frequency modulation present in Doppler ultrasound signals may allow differentiation between particulate and gaseous cerebral emboli. Ultrasound Med Biol 1997;23:727–734.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.