Figure 1.

The stiffness estimation framework begins with the acquisition of two gravity loaded image volumes (see figure 2). A rigid alignment between the two configurations is performed using only chest wall intensity information. The rigid registration procedure results in a translation, t, and rotation, R, that is used to transform I_g1 to be rigidly aligned with the chest wall in I_g2 (see figure 4). Also from R, a change in gravitational loading is quantified. A FEM mesh and biomechanical model is built from I_g2. A displacement field is generated from solving the biomechanical model and is used to deform I_g2. An image similarity metric is calculated between the model deformed image $(I_{g2}^{\prime })$ and the rigidly aligned baseline image (I_g1→g2). Stiffness properties are extracted when the calculated image similarity is optimized. An optimization procedure can be employed to iteratively update the material properties until the image similarity metric is minimized.