Ultrasound strain imaging based on information theoretic delay estimation

Ultrasound strain imaging has great importance as tumor or cancerous tissues are much stiffer than normal tissues. Estimations of strain calculating the time delays between consecutive ultrasound echo signals are common approaches in quasi-static elastography. Because of the ill posed nature of strain images, the ultrasound strain estimation still remains challenging. In this paper, we present an iterative strain estimator that uses mutual information between stochastic pre and post compressed radio frequency (RF) signals to define time delays. For each RF signal, a past and future is defined by cutting sample sequences into two parts. The time delay is considered to be the time shift between the cutting moments for which the mutual information between both past vectors and future vectors reaches a minimum. Displacement calculation with this time delay provides effective strain estimation for small strains. A synthetic phantom of tissue with tumor is modeled using the finite element method (FEM) and the pre-/post-compressed RF signals are generated using ultrasound simulation package Field II. Using these simulated RF data displacements and strain of deformation are calculated in MATLAB. The Contrast to Noise Ratio (CNR) and Signal to Noise Ratio (SNR) are found better compared to conventional cross-correlation method. This algorithm can detect inclusions having echogenicity very close to that of the surrounding tissues and hence can be useful for detection of tumors or cancers.