Wavelet transform-based strain estimator for medical imaging

A new signal processing algorithm based on a Wavelet Transform (WT) is proposed for instantaneous strain estimation in acoustic elastography, where the interior elasticity distribution of a biological tissue is imaged. The proposed estimator weights ultrasonic echo signals acquired before tissue compression by a Gaussian window function and uses the resulting waveform as a mother wavelet to calculate the WT of the postcompression signal. Strain is estimated from the location of the WT peak in the time-frequency domain. To analyze the performance of the proposed estimator, strain errors are investigated. Estimates are shown to be unbiased while variances depend on the echo signal-to-noise ratio, bandwidth, time-bandwidth product, and the applied strain. The results are compared with those obtained from the current strain estimator based on time-delay estimates. The proposed estimator has the advantage of producing unbiased strain estimates with greater precision and potentially higher spatial resolution, dynamic ranger and sensitivity at the expense of increased computation time.