computational grid for the simulation of each scan line.</p>

<a name="heading3"></a>
<h2>Defining the scattering medium</h2>

<p>The contrast in an ultrasound image is generated by acoustic reflections from changes in impedance (sound speed and density). Within the human body, these heterogeneities occur across multiple length scales. At a macroscopic level, different tissue types such as fat or muscle have different bulk material properties. Specular and diffractive scattering from heterogeneities on this