On the influence of external force induced by the ultrasound probe on internal carotid artery elastography features

Carotid strain imaging aims to quantify the deformation and translation (motion) of the artery wall and plaque. Due to changes in boundary conditions, external manual forces may induce a bias in the estimation of carotid artery mechanical properties. The purpose of this study was to investigate the impact of the compression force induced by the ultrasound probe during scanning on measured mechanical properties. Nine volunteers underwent an elastography exam of their left internal carotid artery (LICA) using a custom made force feedback handles that allowed the sonographer to control the pressure applied by the probe on the skin. The force was first recorded during normal scanning, as per operator standard practice (SP). Then, predefined compression (PDC) forces were adjusted with sound feedback to randomly selected values between 2, 4, 6, 8, 10, and 12 Newton. Radiofrequency images were acquired and converted to B-mode for automated wall segmentation. Six carotid elastography features were assessed on upper and lower walls. Results indicated that the sonographer under SP scanned with a force of 6.4 ± 1.6 Newton. Statistically significant negative linear regressions were observed between the applied force and every elastography features on the upper wall, and with only the cumulated lateral translation on the lower wall. One way ANOVA showed that some features were significantly different between PDC versus SP. In summary, slightly negative linear influence of the applied pressure on elastography features was observed. The variation of all elastography features as a function of the probe pressure mainly affected upper wall measurements.