Effects of frame rate on 3D speckle tracking based measurements of myocardial deformation

Myocardial strain has been shown useful in the evaluation of left ventricular (LV) function using 2D and 3D speckle tracking echocardiography (STE). 3D STE is potentially more accurate, because it is not affected by through-plane motion. While with 2D STE, high frame rates are necessary because speckles may move out of the imaging plane, we hypothesized that they should be tracked with 3D STE, even with lower frame rates, because they always remain within the scan volume. Sixteen normal volunteers underwent 2D (at 62±9 fps) and 3D imaging, which was performed at 4 different frame rates, achieved by varying the number of beats used for volume acquisition (6, 4, 2 and 1). The principal components of strain and the corresponding strain-rates were calculated from both 2D and 3D images. Strain and strain-rates were the same for 3D STE with 6- and 4-beat datasets, corresponding to 25 and 18 fps, respectively, and were not significantly lower than 2D STE-derived values, indicating that there was no loss of information due to lower frame rates. In contrast, 3D STE with 1- and 2-beat datasets, corresponding to 5 and 10 fps, resulted in significantly lower values. 3D STE strains and strain-rates are not compromised by low frame rates, when derived from 18 or 25 fps datasets, but are underestimated with lower frame rates.