Comparison of a 1-MHz and a 2-MHz probe for microembolus detection using transcranial Doppler ultrasound

Objectives: Clinically silent microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). There is theoretical evidence that lower ultrasound emission frequencies may lead to a higher signal intensity and thus sensitivity to detect MES. We compared a 1-MHz probe with a 2-MHz...

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Published in:	Neurological research (New York) Vol. 27; no. 5; pp. 471 - 476
Main Authors:	Droste, Dirk W., Lerner, Thomas, Dittrich, Ralf, Ritter, Martin, Ringelstein, E. Bernd
Format:	Journal Article
Language:	English
Published:	England Taylor & Francis 01.07.2005 Maney Publishing
Subjects:	Adolescent Adult Aged CEREBRAL BLOOD FLOW Dose-Response Relationship, Radiation EMBOLISM Female Humans Intracranial Embolism - diagnostic imaging Male Middle Aged Middle Cerebral Artery - diagnostic imaging Observer Variation Reproducibility of Results Sensitivity and Specificity Signal Processing, Computer-Assisted Time Factors ULTRASONICS Ultrasonography, Doppler, Transcranial - instrumentation Ultrasonography, Doppler, Transcranial - methods
ISSN:	0161-6412, 1743-1328
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Summary:	Objectives: Clinically silent microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). There is theoretical evidence that lower ultrasound emission frequencies may lead to a higher signal intensity and thus sensitivity to detect MES. We compared a 1-MHz probe with a 2-MHz probe regarding sensitivity in the detection of MES. Moreover, embolus detection by transcranial Doppler ultrasound is very time consuming and semi-automated detection is mandatory. Therefore, we studied an on-line algorithm using the bi-gate technique and the two transmission frequencies. Methods: After defining detection thresholds of ≥ 12 dB (1 MHz) and ≥ 10 dB (2 MHz) with eight normal subjects as MES-negative controls, taking into account natural fluctuations of the Doppler spectrum, we studied 36 patients with ischaemic events and five asymptomatic patients with incidental embolic sources. All patients subsequently underwent a 1-hour unilateral embolus detection from the middle cerebral artery (MCA) or the posterior cerebral artery (PCA), respectively, using 1 and 2 MHz for 30 minutes each in a randomized order. The software algorithm was compared with a blinded off-line analysis by an experienced observer as a gold standard. Results: The investigator detected 198 MES (range 0-41 MES) in the recordings of 29 patients out of the 41 patients using the 1-MHz probe and 101 MES (range 0-32 MES) in the recordings of 14 patients using the 2-MHz probe (p=0.0007). Sensitivity of the software to detect MES confirmed by the investigator was 31% using 1 MHz and 41% using 2 MHz. The positive predictive value was 6 and 30%, respectively. Discussion: The sensitivity and positive predictive values of the automated algorithm to detect MES were unacceptably low for clinical practice with both frequencies. The use of 1 MHz instead of 2 MHz may, however, be useful when evaluating the recordings off-line by an experienced blinded observer.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-General Information-1 content type line 14 ObjectType-Feature-3 ObjectType-Article-1 ObjectType-Feature-2 content type line 23 ObjectType-Feature-1
ISSN:	0161-6412 1743-1328
DOI:	10.1179/016164105X15695