3D ultrasound imaging of tissue anisotropy using spatial coherence: Comparison between plane and diverging waves

The heart, like skeletal muscles, is made up of muscular cells arranged regularly and packed into sort of bundles commonly called cardiac fibers. After a myocardial infarction (MI) both during the acute phase and the reperfusion of the myocardium, several cells die and some local fibers orientation modifications appear. Consequently, the heart does not contract properly anymore. The evaluation of the fibers orientation and more particularly the modifications of their orientation can be useful to evaluate the extent of the lesion and to adapt the treatment after a MI. The purpose of our work is to develop ultrasound based imaging techniques to determine the cardiac fibers orientation in order to be able in fine to determine fibers orientation changes that appear due to MI. Recently, a fiber orientation ultrasound imaging technique has been proposed based on the spatial coherence of backscattered signals. In this paper, we study the spatial coherence technique in ultrafast imaging. We evaluate the feasibility to extend the previous published technique to diverging waves instead. The purpose is to extend the field of view which is typically reduced in cardiac imaging due to the limited ultrasound window possible between the ribs. Experimental data were acquired with a 1024 channels system and a 32×32 matrix array on a phantom constituted by seven wires at different orientations as a function of depth. These first results obtained with two different transmission strategies are compared and are in favor of diverging waves.