Variability of Shear Wave Velocity using Different Frequencies in Acoustic Radiation Force Impulse (ARFI) Elastography: A Phantom and Normal Liver Study

Abstract

Purpose: To assess the variability of shear wave velocity (SWV) from acoustic radiation force impulse (ARFI) elastography at various depths using different frequencies.

Materials and Methods: ARFI elastography of the elasticity phantom and normal liver was performed at different depths (2 – 5 cm) with convex (1 – 4 MHz) and linear (4 – 9 MHz) probes. Ten valid SWV measurements at each depth were performed. This was repeated ten times with the phantom and performed in eight healthy volunteers (M:F = 3:5, age 20 – 34 years). The mean value and standard deviation of the SWV were calculated.

Results: In both the phantom and liver, the mean velocities as measured by two probes at the same depth were different. Variabilities of SWV at different depths were also different for the two probes. The depth with lower variability in the phantom was 4 and 5 cm with a convex probe and 2 cm with a linear probe. In the liver, the depth with lower variability was 4 cm with a convex probe and 3 and 4 cm with a linear probe. In comparative analysis of the two probes, the linear probe displayed a lower variability at a depth of 2 and 3 cm in the phantom and at 3 cm in the liver, whereas the convex probe displayed a lower variability at a depth of 4 cm in both the phantom and the liver.

Conclusion: SWVs and variability are different depending on the depth and the frequency used. SWVs with a low frequency probe had a tendency to be higher at the same depth. To reduce variability of SWV, a high frequency probe is recommended for a depth of 2 – 3 cm, and a low frequency probe is recommended for a depth of 4 – 5 cm.

Zusammenfassung

Ziel: Die Bewertung der Schwankung der Scherwellen-Geschwindigkeit (SWG) bei der ARFI (Acoustic Radiation Force Impulse)-Elastografie bei verschiedenen Messtiefen und unterschiedlichen Frequenzen.

Material und Methoden: Die ARFI-Elastografie des Elastizitätsphantoms und der Leber wurde bei verschiedenen Messtiefen (2 – 5 cm) mit konvexen (1 – 4 MHz) und linearen (4 – 9 MHz) Schallköpfen durchgeführt. Zehn gültige SWV Messungen wurden in jeder Tiefe durchgeführt. Diese wurden zehn Mal am Phantom und bei acht gesunden Freiwilligen wiederholt (M:F = 3:5, Alter 20 – 34 Jahre). Die Mittelwerte und Standardabweichungen der SWG wurden berechnet.

Ergebnisse: Sowohl beim Phantom als auch bei der Leber wurden mit den beiden Schallköpfen bei gleicher Tiefe unterschiedliche mittlere Geschwindigkeiten gemessen. Die Schwankungen der SWG bei verschiedenen Tiefen waren mit den beiden Schallköpfen unterschiedlich. Beim Phantom betrug die Messtiefe mit der geringeren Schwankung 4 und 5 cm für den konvexen Schallkopf und 2 cm für die lineare Sonde. In der Leber betrug die Tiefe mit der geringeren Schwankung 4 cm für die konvexe und 3 und 4 cm für die lineare Sonde. In der vergleichenden Analyse der beiden Schallköpfe zeigte die Linearsonde eine niedrigere Schwankung bei Tiefen von 2 und 3 cm im Phantom und von 3 cm in der Leber, während der konvexe Schallkopf geringere Schwankungen bei Tiefen von 4 cm sowohl beim Phantom als auch in der Leber zeigte.

Schlussfolgerung: Die SWGs und Schwankungen unterscheiden sich je nach Messtiefe und Frequenz. Die SWGs bei Verwendung von Niedrigfrequenz-Schallköpfen tendieren dazu, bei der gleichen Messtiefe höher zu sein. Um die Schwankungen der SWG zu verringern, wird empfohlen, einen Hochfrequenz-Schallkopf bei einer Tiefe von 2 – 3 cm und einen Niedrigfrequenz-Schallkopf bei einer Tiefe von 4 – 5 cm zu verwenden.

Key words

acoustic radiation force impulse-imaging - phantom - liver - variability

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