Established standard methods in diagnostic ultrasound imaging, such as B-mode, beam forming using delay-and-sum (DAS) and synthetic aperture methods (SA), are based on highly simplified physical models for the propagation of sound waves in biological materials. These simplifications can lead to unwanted image artifacts, which considerably complicate a correct interpretation of the ultrasound images. Furthermore, it is not clear which mechanical parameters of the investigated inhomogeneous biological material are mapped.
The Chair of Medical Engineering therefore develops imaging methods that take the propagation, reflection and diffraction of sound waves in biological materials into account. Such methods are based on (linearized) wave equations for soft tissue (inhomogeneous fluids) or bone structures (inhomogeneous solids).
Tomographic reconstruction of simulated ultrasound data. Transducers are arranged in a ring structure. Left: Simulated ultrasonic phantom, Right: Result of the reconstruction
In the context of the models developed, the term imaging means the graphical representation of the inhomogeneous material parameters. The latter are to be determined from measurements of the reflected and scattered sound waves. The solution of these so-called inverse problems is generally not trivial and requires the application of advanced mathematical methods and complex algorithms.