Ultrasound strain imaging: From nano-scale motion detection to macro-scale functional imaging

With ultrasound strain imaging, the function of tissue and organs can be identified. The technique uses multiple images, acquired from tissue under different degrees of deformation. We recently applied this technique on hearts and skeletal muscles. Cardiac data was acquired in dogs with a valvar aorta stenosis. Muscle data was acquired from the orbicular oral muscle in the upper lip. For accurate assessment of deformation, the displacement of tissue can be determined at nanometer scale. Raw ultrasound data, containing the amplitude as well as the phase information is required for this analysis. A 2D coarse-to-fine strain estimation strategy is proposed to calculate the minute differential displacements in tissue, while the tissue itself is moving on a macro scale. The technique was validated using phantom experiments. These experiments demonstrated that accurate strain images can be determined using the proposed technique. Cardiac evaluation in dogs showed that the strain can be determined in three dimensions. The strain curves over the cardiac cycle are in correspondence with the severity of the stenosis of the aortic valve. In patients with a reconstructed cleft lip, the orbicular oral muscle in the reconstructed region showed decreased strain values. In normal individuals, similar strain values were found for all regions of the muscle. Ultrasound strain imaging is a promising technique enabling the addition of functional information to the geometrical information that is already provided by the conventional ultrasound imaging technique.