Fig 1.
(A) Experimental setup for biaxial testing combined with 3D ultrasound scanning. X: lateral, Y: elevational (scanning), Z: axial (ultrasound propagation) direction of the ultrasound transducer. Note that the 3D speckle tracking and the displacement/strain estimation follow this coordinate. (B) The excised section of right ventricular free wall (RVFW) for biaxial testing. X: cross-preferred (circumferential) direction; Y: apex-to-outflow-tract (longitudinal) direction. Note that the X and Y in ultrasound transducer coordinate and the RVFW sample coordinate match respectively.
Fig 2.
(A) Typical real time force vs. actuator displacement plot measured by the biaxial tester on right ventricular free wall (RVFW). The displacement increment between two consecutive stretch steps was 70 μm. Representative (B) lateral, (C) axial, and (D) elevational displacements estimated in the middle section (X-Z) of RVFW sample by 3D-UST between two consecutive stretch steps at actuator force of 85 mN indicated by the arrow in (A).
Fig 3.
Green Lagrangian normal strain (E) obtained by 3D ultrasound speckle tracking (3D-UST) vs. second Piola-Kirchhoff normal stress (S) plots obtained by biaxial testing from epi- to endo-cardium for (A) normotensive right ventricular (RV) samples and (B) pulmonary hypertension (PH) RV samples. The error bar represents the standard deviation of average Green Lagrangian normal strains obtained from 9 normotensive RV samples and 6 PHRV samples. The normal strain (EXX) and normal stress (SXX) in circumferential direction, and normal strain (EYY) and normal stress (SYY) in longitudinal direction are presented together in the same plot for comparison.
Table 1.
The average SEF coefficients for normotensive RV samples and PHRV samples.
Fig 4.
Representative reconstructed fiber orientations of (A) normotensive and (B) PHRV samples. The fiber orientation angle was defined as Y: outflow tract (0°) and X: septum (-90°). The fiber orientations obtained by 3D-UST (red solid lines) overlaid with ultrasound images compared with histology-quantified fiber orientations (solid blue lines) overlaid with corresponding histological images at near the epi-cardium, middle myocardium and near the endo-cardium.
Fig 5.
The average fiber angles computed by 3D ultrasound speckle tracking (3D-UST)-biaxial experiment, and those quantified by histology from epi- to endo-cardium for (A) normotensive right ventricular free wall (RVFW) samples and (B) pulmonary hypertension right ventricular (PHRV) samples. The error bar represents the standard deviation of average fiber angles obtained from 9 normotensive right ventricular samples and 6 PHRV samples.
Fig 6.
Green Lagrangian normal strain (E) vs. second Piola-Kirchhoff normal stress (S) plots measured from (A) normotensive right ventricular (RV) and (B) pulmonary hypertension RV (PHRV) samples for visually tracking markers (VTM) and 3D ultrasound speckle tracking (3D-UST). The error bar represents the standard deviation of average Green Lagrangian normal strains.
Fig 7.
The Bland-Altman plots showing the differences of normal strains between the VTM and 3D-UST.
The middle red solid line indicates the mean difference of normal strains and the upper and lower red dotted lines represent 95% limit of agreement for the two measurements.