Shear Wave Elastography May Be Superior to Greyscale Median for the Identification of Carotid Plaque Vulnerability: A Comparison with Histology

Abstract

Purpose: There is a need to develop methods that reliably quantify characteristics associated with vulnerable carotid plaque. Greyscale median (GSM) and shear wave elastography (SWE) are two techniques that may improve individual plaque risk stratification. SWE, which quantifies Young’s Modulus (YM) to estimate tissue stiffness, has been researched in the liver, breast, thyroid and prostate, but its use in carotid plaques is novel.

Materials and Methods: The aim of this study was to quantify YM and GSM of plaques and compare to histology. 25 patients (64 % male) with a mean age of 76 underwent both clinical and SWE imaging. The mean GSM was quantified over a cardiac cycle. The mean YM was quantified in multiple regions within the plaque over 5 frames. Histological features were assessed following carotid endarterectomy.

Results: The mean YM of unstable plaques was significantly lower than that of stable plaques (50.0kPa vs. 79.1kPa; p = 0.027). The presence of intra-plaque hemorrhage, thrombus and increasing numbers of foam cells was also associated with a significantly lower YM. Plaque YM did not correlate well with plaque GSM (r = 0.12). The mean plaque GSM was the same in both unstable and stable plaques. Fibrous plaques had a significantly higher GSM (p = 0.036).

Conclusion: In conclusion, SWE provides additional information on plaque stiffness which may be of clinical benefit to help identify vulnerable plaque, and warrants further study.

Zusammenfassung

Ziel: Es müssen dringend Methoden entwickelt werden, die verlässlich Merkmale in Zusammenhang mit der Vulnerabilität von Karotisplaques quantifizieren. Der mediane Grauwert („grey-scale median“ GSM) und die Scherwellen-Elastografie sind zwei Methoden, die eine Stratifizierung des individuellen Plaquerisikos verbessern könnten. Die SWE, die den Youngschen Modul (YM) zur Bewertung der Gewebesteifigkeit quantitativ bestimmt, wurde bei Leber, Brust, Schilddrüse und Prostata untersucht, deren Anwendung bei Karotisplaques ist jedoch neu.

Material und Methoden: Ziel der Studie ist die Quantifizierung von YM und GSM in Plaques im Vergleich zur Histologie. Bei 25 Patienten (64 % Männer) mit einem mittleren Alter von 76 Jahren wurden jeweils klinische bildgebende Verfahren und SWE durchgeführt. Der mittlere GSM wurde über einen Herzzyklus quantifiziert. Der mittlere YM wurde in mehreren Regionen innerhalb der Plaque über 5 Einzelbilder quantifiziert. Die histologischen Befunde wurden im Anschluss an die Karotisendarterektomie erhoben.

Ergebnisse: Der mittlere YM der unstabilen Plaques (50,0 kPa) war signifikant niedriger als derjenige der stabilen Plaques (79,1 kPa; p = 0,027). Das Vorliegen von Intra-Plaque-Blutungen, Thromben und eine ansteigende Zahl von Schaumzellen waren auch mit einem signifikant niedrigeren YM assoziiert. Der YM der Plaque zeigte eine weniger gute Korrelation mit dem Plaque-GSM (r = 0,12). Der mittlere Plaque-GSM von unstabilen und von stabilen Plaques war gleich. Fibröse Plaques zeigten einen signifikant höheren GSM (p = 0,036).

Schlussfolgerung: Die SWE gibt Zusatzinformationen über die Plaque-Steifigkeit, die für die Identifikation vulnerabler Plaques von klinischem Nutzen sein können, was weitere Studien rechtfertigt.

Key words

carotid arteries - blood vessels - vascular - ultrasound - ischemia/infarction

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