Estimation of Longitudinal Shear Strain in the Carotid Arterial Wall Using Ultrasound Radiofrequency Data

Zusammenfassung

Ziel: Der primäre Auslöser für einen Myokardinfarkt oder Schlaganfall ist eine Mobilisierung von arteriosklerotischen Plaques. Es wird vermutet, dass Scherdehnungsmechanismen (Shear Strain) in der Adventitia die Entwicklung hin zu brüchigen, instabilen Plaques initiiert und/oder stimuliert. Daher könnte die Untersuchung der Scherdehnung eine Prognoseeinschätzung bezüglich der Entwicklung von instabilen Plaques ermöglichen. Material und Methoden: Mithilfe von Simulationen und Phantom-Experimenten wurde die Scherdehnung mittels Radiofrequenz(RF)- und Envelope-basierten Methoden ermittelt und mit den angewandten Werten verglichen. Zusätzlich wurden Scherdehnungssmessungen in der Adventitia von 6 gesunden Probanden vorgenommen. Ergebnisse: In beiden Experimenten war die Varianz der RF-basierten Werte deutlich kleiner als die der Envelope-basierten Werte (Wilcoxon, p < 0,05). Die Periodizität der Scherdehnungswerte der Probanden stimmte gut mit dem jeweiligen Herzzyklus überein. Die ermittelten Werte waren bereits zuvor publizierten Daten vergleichbar. Darüber hinaus war die Signal-Rausch-Rate der Scherdehnungswerte in der hinteren Gefäßwand, die mit der RF-basierten Methode ermittelt wurden, signifikant höher als die auf Basis der Envelope-Methode ermittelten Werte (Wilcoxon, p < 0,05). Schlussfolgerung: Nicht invasiver Ultraschall mit radiofrequenzbasierten Methoden scheint geeignet zu sein, die Scherdehnung in der Adventitia der Arteria carotis zu bestimmen.

Abstract

Purpose: The primary trigger for myocardial infarction and stroke is destabilization of atherosclerotic plaques. It is hypothesized that shear strain in the adventitia initiates and/or stimulates development of these plaques into rupture-prone, vulnerable plaques. Therefore, assessment of shear strain might yield a prognosis for the development of vulnerable plaques. Materials and Methods: In simulations and phantom experiments, longitudinal shear strain was estimated using RF and envelope-based methods and compared to the applied values. Additionally, longitudinal shear strain estimates in the adventitia of six healthy volunteers were determined. Results: In both experiments, the variance of the RF-based estimates was significantly smaller than that of the envelope-based estimates (Wilcoxon, p < 0.05). The periodicity of these estimates corresponded well with the cardiac cycle. The estimated values were found to be similar to previously published data. Furthermore, the signal-to-noise ratio of the shear strain estimate in the posterior wall based on RF-data was significantly higher (Wilcoxon, p 0 < 0.05) than that based on envelope-data. Conclusion: In conclusion, noninvasive ultrasound strain imaging using radiofrequency signals appeared to allow adequate estimation of longitudinal shear strain in the adventitial layer of the carotid artery wall.

Key words

carotid arteries - ultrasound - arteriosclerosis

References

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