At Forschungszentrum Karlsruhe an Ultrasound Computer Tomography system USCT) is under development for
early breast cancer detection. To detect morphological indicators in sub-millimeter resolution, the visualization
is based on a SAFT algorithm (synthetic aperture focusing technique). The current 3D demonstrator system
consists of approx. 2000 transducers, which are arranged in layers on a cylinder of 18 cm diameter and 15 cm
height. With 3.5 millions of acquired raw data sets and up to one billion voxels for an image, a reconstruction
may last up to months.
In this work a performance optimized SAFT algorithm is developed. The used software environment is
MathWorks' MATLAB. Several approaches were analyzed: a plain M-code (MATLAB's native language), an
optimized M-code, a C-code implementation, and a low-level assembler implementation. The fastest found
solution uses an SIMD enhanced assembler code wrapped in the C-interface of MATLAB. Additionally a 10%
speed up is gained by reducing the function call overhead. The overall speed up is more than one order of
magnitude. The resulting computational efficiency is near the theoretical optimum. The reconstruction time is
significantly reduced without losing MATLAB's comfortable development environment.
The point spread function (PSF) of an imaging system may be used as measure for the imaging quality. The PSF usually depends on position and an several other system parameters. Our current 3D imaging system for ultrasound computer tomography consists of a rotatable cylinder with approx. 2000 ultrasound transducers. 3D images are reconstructed by means of synthetic aperture focusing technique (SAFT) using all available emitter-receiver-combinations. No analytical solution exists for determining the spatially varying PSF for arbitrary placement of the transducers.
This work derives a new numerical approach for the approximation of the 3D PSF for arbitrary transducer geometries including the beam pattern of the ultrasound transducers, a directional point scatterer model, damping of the breast and arbitrary pulse shapes.
As an exemplary application the spatially varying 3D PSF of the current cylindrical geometry is analyzed under idealized conditions (point sources, no damping, and isotropic scattering) and compared to non-idealized results of the PSF analysis. The results show the necessity to take the system specific parameters into account for a realistic
prognosis of 3D imaging performance.