BiPlane cardiac strain imaging: A study on valvular aortic stenosis

In this study, the first preliminary results are reported of a beagle study on valvular aortic stenosis using BiPlane strain imaging. A previously reported strain method was applied to BiPlane RF-data of the heart of four beagles. A window-level tracking algorithm was devised, using a neighbour-based regularization force and a weighting factor that is highly depended on the cross-correlation values. The tracking method was tested on a thick wall tube phantom that was heavily translated in axial and lateral direction, while the intraluminar pressure was varied. Four healthy beagles underwent surgery at the age of six weeks. One cusp of the aortic valve was fixated to the arterial wall. Raw (RF) ultrasound data of the beagles' heart were acquired monthly with a Philips SONOS 7500 live 3D ultrasound system, equipped with an X4 matrix array transducer and an RF-interface. BiPlane data were acquired using ECG-triggering at a frame rate of 100 Hz for at least one complete heart cycle. Histological analysis of the heart muscle was performed after termination. ROIs in the lateral wall in both the short and long axis view were manually segmented and subsequently tracked. Displacements and strains were calculated and the ROIs were tracked using the proposed method. In the phantom, each pixel within the ROI was tracked separately. The local strains were reconstructed correctly after tracking, despite large translations and deformations. In the animals, the strain curves were consistent with strain imaging results obtained in other animal and human studies. Furthermore, the strain curves showed less drift and higher peak strain values after tracking. Histological findings confirmed a successful creation of a valvular aortic stenosis and revealed a positive relation between severity of valvular aorta stenosis and the total amount of collagen. The corresponding mean maximum radial indicated a negative relation between pressure and strain.