A model for ultrasonic scattering from tissues based on the K distribution.

A model for the backscattered ultrasound echo from tissues is presented. The model takes into account the fact that the range cell being insonified may contain only a few scatterers and the number may not be large enough to justify the use of a Gaussian model which results in Rayleight statistics for the echo. Furthermore, the model also considers the case where the echogenicity of the scatterers in the range cell may not be uniform, the lack of uniformity resulting from variations in scattering cross-sections produced by the chemical as well as biochemical changes brought on by the presence of disease, growth of benign or malignant tumours, etc. The model is developed from the fundamental principles of scattering using the results available in radar. This new model results in a two-parameter distribution, namely the K distribution for the echo, thereby making it possible to gain information on the number as well as scattering cross-sections of the scatterers in the range cell. The model is extended to include the effects due to the presence of scatterers having some regular or periodic orientation in the range cell, resulting in the so-called generalized K distribution which approximates to Rayleight, Rician, or Gaussian under various limiting cases. Results of computer simulations and experiments on tissue-mimicking phantoms are also provided, which strongly suggest that this new model offers potential for tissue characterization.