Abstract: During ultrasound checking of the results of lithotrity performed on biliary calculi, it is difficult to distinguish a calculus from crush. This problem is mitigated in accordance with the invention in that the ultrasound transducer (6) used for performing the ultrasound observation first receives a comparatively high electric power for a comparatively long period of time. As a result, the biliary calculus (4) or the crush is stirred up in the gallbladder (3); the size of the particles can be determined from the differences in behavior during settling in the gallbladder.