Three-dimensional myocardial strain estimation from volumetric ultrasound data using a novel transformation model adapted to the heart

We previously demonstrated that 3D cardiac strain estimation using non-rigid registration based on a B-spline freeform deformation model (FFD) is feasible. However, the traditional arrangement of the B-spline control points on a Cartesian grid (CFFD) may be suboptimal for cardiac applications as it treats the blood pool and myocardium similarly and as it enforces smoothness in non-physiologic directions. The aim of this study was therefore to overcome these limitations by proposing a novel anatomical FFD (AFFD) adapted to the heart and test its performance experimentally. Volumetric data was recorded in gel phantoms and in 5 sheep. Reference radial (ϵ_RR), longitudinal (ϵ_LL) and circumferential strain (ϵ_CC) were obtained using sonomicrometry. The strain range was modulated by increasing the stroke volume (phantoms; 25-150ml) or by (pharmacological/surgical) inotropic modulation (sheep). Correlation coefficients for ϵ_RR, ϵ_LL and ϵ_CC were 0.98, 0.62 and 0.94 respectively in the phantom data and 0.87, 0.65 and 0.74 respectively in the sheep data. Moreover, the shape of the strain curves, timing of peak values and location of dysfunctional regions were recovered well. Further validation and its comparison to the CFFD model is the topic of ongoing research.