The Influence of Angle of Insonation and Target Depth on Speckle-Tracking Strain

Abstract

Speckle-tracking strain is almost universally cited as being independent of angle of insonation, but there are minimal confirmatory studies, and this claim may not be consistent with the known limitations of ultrasound axial and lateral spatial resolution. The aim of this study was to assess the influence of angle and depth on longitudinal peak systolic strain (LPS). Thirty-four healthy pediatric subjects (age range, 6-18years; 47% male) with normal cardiac anatomy and good image quality were prospectively imaged. Angular comparisons of LPS were investigated by examining interangle reproducibility on the basis of one standard and one alternative image acquisition relative to intraobserver reproducibility of two standard views of the same left ventricular segments. A single-window comparison was used to evaluated septal LPS: standard apical four-chamber versus right ventricular centered four-chamber. Two paired standard and alternative window comparisons were as follows: (1) four-chamber: standard apical versus subcostal; and (2) three-chamber: standard apical versus parasternal long-axis. The global LPS intraobserver difference using the paired standard and alternative window comparisons was lower than the interangle difference in global LPS (-1.0 ± 0.1% vs -2.1 ± 2.4%). Intraobserver reproducibility was significantly higher than interangle reproducibility (intraclass correlation coefficient=0.9 vs 0.29, P<.001). Similar results were found in the segmental strain analysis. Interangle reproducibility was significantly decreased compared with intraobserver reproducibility in the septal single-window comparison. Target depth assessment demonstrated a systematic bias between the near-field and far-field segments. Echocardiographically derived LPS values were modestly dependent on angle of insonation and target depth in this pediatric population. Normal strain ranges derived from standard apical images should not be applied to strain derived from sub-costal images, off-axis apical imaging, or applications in which a standard window cannot be defined.