Doctoral Theses

Coherent High-Resolution Ultrasound Reflection Mode CT Imaging

Juha Ylitalo, Ph.D. June 1987

University of Oulu, Oulu, Finland


A coherent high-resolution ultrasound reflection mode CT imaging method has been developed for imaging small restricted areas Inside objects such as liver. The high spatial resolution of the method results from a large, fully enclosing imaging aperture and coherent signal processing. Since only a single radial scan and common straight-line CT reconstruction are required, the processing time and computer as well as hardware requirements are reduced considerably compared to those of ordinary transmission or reflection CT. The main limitation of the method is the need for correction for speed variations in an intervening medium. This is done by tracing "brightest" sinusoids in the Radon space of the data to obtain estimates of the time shifts.

Images of simulated objects, real phantoms, and liver specimens are presented and, in experiments with tissues, compared to images obtained by compound B-scans from exactly the same cross-sectional planes of the object. Experiments show that the new imaging method is operational and that the spatial resolution of about 0.3 mm can be achieved using a commercial 3.5 MHz transducer.


  • acoustical imaging
  • computerized tomography
  • image reconstruction