Principles of sonoelasticity imaging and its applications in hard tumor detection

A novel imaging technique named "sonoelasticity imaging" has been proposed and its applications in hard tumor detection is explored in this research. A low frequency (10-1000 Hz) external vibration source is applied to excite the internal tissue motion and the local velocities of tissue vibration are detected by Doppler ultrasound. Elastic properties of deep tissue are inferred by their response to the vibration. Hard tumors are distinguished from surrounding soft tissues by their different vibration response due to distinct elastic properties.;A number of questions must be answered before sonoelasticity imaging can become a useful clinical tool. These questions are: (1) What are the elastic properties of normal and cancerous tissue? (2) What is appropriate signal processing for the Doppler detection of vibration? (3) What are appropriate vibration source frequencies and spatial distributions? (4) How do the vibration patterns relate to local changes in elastic parameters? The goal of this research is to contribute a deeper understanding of these problems.;The problem of internal tissue vibration detection by Doppler ultrasound is formulated as a frequency modulation (FM) process. A new and general relationship between the baseband modulating signal spectrum and moments of FM power spectrum is disclosed. Novel frequency and time domain estimation techniques are proposed and evaluated through simulations. Measurements on the nonlinear stress-strain relationship, hysteresis, and preconditioning are made for phantoms and tissue specimens. Existing color Doppler imaging instruments are modified to display sonoelasticity images. Phantoms, prostate specimens from autopsy and surgery, liver with/without VX2 tumor are sonoelasticity-imaged in vitro. Modal patterns in regular geometry are observed and analyzed. Numerical analysis of hard and soft tissues responses is performed and compared with the experimental results.