Feasibility of reproducible vendor independent estimation of cardiac function based on first generation speckle tracking echocardiography

Abstract

Background: The clinical approval of speckle tracking echocardiography (STE) as an accepted measure of myocardial strain and of LV function is hindered by the discordance of the results among the vendors. Since echocardiography images are noisy, the measured displacements are smoothed or regularized, an operation affecting the strain results. We introduce an “Error-dependent weighted speckle tracking” (EWST) algorithm that allows sensitivity analysis to the different operations affecting noise and accuracy. The aim here was to study whether by modifying the properties of the post block-matching weighted smoothing in the EWST algorithm it was possible to assess the expected inter-vendor strain differences.

Methods and results: 48 echocardiographic clips generated by a software-based phantom were used as “gold standard” for validation of the EWST algorithm. Also, a cohort of 435 normal subjects and a cohort of 47 patients, scanned/re- scanned at 2 frame-rates (~70; ~35), were studied using the EWST. The results were compared to those produced by a commercial product of a leading manufacturer (STE_LV).  Peak global longitudinal strains [PRLS, (%)] and peak regional longitudinal strains [PRLS, (%)] were calculated and compared. Sensitivity to the region (ROI) determination was tested by shifting the apical endocardial boundary. The differences between the measured PGLS and the ground truth produced by the software-based phantom (average ± standard deviation) were 0.4% ± 0.6% and 1.0% ± 0.7% for the EWST and STE_LV, respectively. Normal values were calculated for 435 subjects: -18.82% ± 2.45%, -20.2% ± 5.6%, -19.62% ± 3.62%, 18.77% ± 4.31% by the EWST, and -21.24% ± 2.91%, -26.5% ± 5.0%, -21.1% ± 3.7%, -18.0% ± 3.9%, by the STE_LV, respectively, for the PGLS, the peak longitudinal apical, mid-ventricle and basal regions, respectively. A low bias, but significant, was found between PGLS, when calculated for the cohort of 47 patients scanned/re-scanned at 2 frame-rates: -0.80% ± 2.61% and -1.66% ± 2.66% for the EWST and STE_LV, respectively. When the apex location (and thus the ROI) was shifted, the bias (mm) (average ± standard deviation) relative to the default position was:  0.82 ± 1.04; 0.61 ± 0.72; -1.06 ± 0.75; and -1.87 ± 0.72, for displacement of 5 cm, 2.5 cm, -2.5 cm, and -5 cm, respectively, for the STE_LV. The EWST proved similarly sensitive to the shifting of the apex location.

Conclusions: STE is sensitive to the characteristics and amount of smoothing, as well as to the ROI positioning. Modification of the smoothing can produce different stain results, and different distribution of the regional strains.  Thus it is preferable to use automatic determination of the ROI and methods that employ minimal smoothing or regularization.