Eighty in vitro experiments were performed with single (n = 51) or multiple (n = 29) gallstones in order to find out which parameters are of prime importance for their disintegration by extracorporeal shock waves. A Dornier lithotripter and an upper limit of 1,500 discharges were employed. Although computed tomography density was significantly lower in cholesterol stones than in the noncholesterol stones (p less than 0.0001) and although the latter were significantly more often radiopaque (p less than 0.0001), we found no clear-cut correlation between the cholesterol content or computed tomography density and the degree of fragmentation of the stones. The most important variable which limited successful disintegration was the total stone volume. In stones with a mean total volume of 0.83 ml +/- 0.25 S.E. (diameter for single stones = 11.5 +/- 0.9 mm), none of the fragments exceeded 2 mm, whereas in stones with a mean volume of 3.6 ml +/- 0.64 (diameter = 17.2 +/- 1.5 mm) at least one fragment larger than 2 mm remained (p less than 0.002). Under the in vitro conditions, fragmentation was similar in multiple and solitary stones, provided the volume of the stones was comparable. These data show that, in general, the number and size of the stones, i.e. their total volume, and much less significantly their chemical composition are the major determinants of fragmentation by extracorporeal shock waves.

A comparative study of the effectiveness of two types of lithotripter in fragmenting gall bladder stones is reported. The machines used were a Piezolith 2300, which generates shock waves by the piezoceramic principle, and a Dornier MPL 9000, which produces the shock waves by underwater spark discharge. With each machine, corresponding stones (Table). Volume was determined by hydrostatic weighing.Computed tomograms were performed on all stones to assess calcification and density. All scans were performed by the same Siemens Somatom DRH. The stones were placed in a container and immersed 3 cm into distilled water. The whole container was scanned with 2 mm slices (125 kV, 720 mas, scan time 5 seconds). On the slice with the largest stone diameter, the border of the calculus was marked by a cursor to determine the region of interest. The computed tomographic densities in this region were processed by computer and the mean value expressed in Hounsfield units (HU).Lithotripsy was performed with the Piezolith 2300 (Richard Wolf GmbH) at the highest setting (setting 4) and with the MPL 9000 (Dornier Medizintechnik GmbH) at 18 kV (80 nF), which was equivalent to the mean power used in patient treatment in former studies.42 The individual stones were placed in a specially constructed test apparatus (Fig 1) which consisted of a plastic basket (2 mm grid) for supporting the stones, placed in a water filled container fitted with a silicone rubber base to allow passage ofthe shock waves. The apparatus was immersed in the Piezolith bowl or, for the MPL 9000, placed in contact with the water cushion so that it lay within the focus of the shock waves. Shock waves were applied until all of the fragments had passed through the 2 mm grid.After fragmentation, samples of 1 to 1.5 mg were subjected to infrared spectrophotometry (Perkin Elmer 377) in order to obtain a qualitative and quantitative estimate of the composition. They were classified as cholesterol stones when the cholesterol content was greater than 70%. ResultsOne stone from each of the 45 pairs of stones was treated in each lithotripter. The pairs were 312 on 11 May 2018 by guest. Protected by copyright.

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