Production of artificial urinary stones from natural materials and their physical properties. First results

The Use of Chemical Treatments for Improved Comminution of Artificial Stones

PURPOSE

The acoustic and mechanical properties of various stone compositions are significantly different and thus result in varying degrees of fragility. Consequently, results to shock wave lithotripsy (SWL) are influenced accordingly. We report the results of a study of fragility of various stone compositions, and the influence on each stone's baseline physical properties and fragility when exposed to various chemolytic solutions.

MATERIALS AND METHODS

Before SWL artificial stones of differing compositions were irrigated with various chemolytic solutions. Calcium oxalate monohydrate (COM) stones were treated with ethylenediaminetetraacetic acid (EDTA), stones composed of magnesium ammonium phosphate hydrogen were treated with hemiacidrin, and stones made of uric acid (UA) were treated with tromethamine. Synthetic urine served as a control for all stone groups. Using an ultrasound transmission technique, longitudinal wave propagation speed was measured in all groups of artificial stones. Stone density was also measured by using a pycnometer (based on Archimedes' principle). Based on these measurements transverse (shear) wave speed (assuming a constant Poisson's ratio), wave impedance and dynamic mechanical properties of the artificial stones were calculated. Moreover, the microhardness of these artificial stones was measured, and fragility testing using SWL with and without pretreatment with the previously mentioned chemolytic solutions, was performed.

RESULTS

Wave speed, wave impedance, dynamic mechanical properties and microhardness of EDTA treated COM stones and tromethamine treated UA stones were found to decrease compared to untreated (synthetic urine) control groups. The suggestion that chemolytic pretreatment increases stone fragility was verified by the finding of increased stone comminution after SWL testing. Combining this medical pretreatment and SWL, the findings demonstrate a significant impact of various solvents on stone comminution, in particular EDTA treated COM stones, tromethamine treated UA stones and hemiacidrin treated magnesium ammonium phosphate hydrogen stones. These data suggest that by altering the chemical environment of the fluid surrounding the stones it is possible to increase the fragility of renal calculi in vitro.

CONCLUSIONS

These results indicate that appropriate chemical treatments may provide a useful adjunctive modality for improving the efficacy of stone comminution during shock wave lithotripsy.

Evaluation of Synchronous Twin Pulse Technique for Shock Wave Lithotripsy: Determination of Optimal Parameters for In Vitro Stone Fragmentation

PURPOSE

The Twinheads extracorporeal shock wave lithotriptor (THSWL) is composed of 2 identical shock wave generators and reflectors. One reflector is under the table and the other is over the table with a variable angle between the axes of the 2 reflectors. The 2 reflectors share a common second focal point, making it possible to deliver an almost synchronous twin pulse to the targeted stone. We studied the optimal parameters for in vitro stone fragmentation.

MATERIALS AND METHODS

Two types of 1 cm artificial stones were used, namely Bon(n)-stones of 3 compositions (75% calcium oxalate monohydrate [COM] plus 25% uric acid, struvite and cystine) and plaster of Paris. The parameters tested were shock wave number (100, 500 and 1,000), shock wave power (8, 11 and 14 kV) and angle between the reflector axes (67, 90 and 105 degrees). After the optimal parameters were determined we studied the disintegrative efficacy of THSWL for 3 types of human urinary calculi, including COM, calcium hydrogen phosphate (brushite) and cystine. Each stone received 1,000 twin shock waves at 14 kV with an angle of 90 degrees between the reflectors. All experiments were done using a rate of 60 twin shock waves per minute. Following lithotripsy stone fragments were processed and sized. The ratio of the weight of fragments greater than 2 mm-to-total weight of all fragments was calculated.

RESULTS

Optimal stone fragmentation results for THSWL were obtained with the maximum number of shock waves (1,000) and full power (14 kV). There was no significant statistical difference in fragment size or the ratio of fragments greater than 2 mm with the use of different angles except for cystine and plaster of Paris calculi, for which the right angle was most effective. At application of the optimal parameters to human stones THSWL produced small fragment size for COM and cystine stones, while brushite stones were not fragmented to the same extent.

CONCLUSIONS

The efficacy of synchronous twin pulse technology improves as the number of shock waves and power increase. A 90-degree angle between the shock wave reflectors is advantageous for certain stones (that is cystine and plaster of Paris) but it is not a factor for other stone compositions. THSWL has satisfactory disintegrative efficacy for human stones, especially COM and cysteine calculi.

Combining Lithoclast and ultrasound power in one device for percutaneous nephrolithotomy: in vitro results of a novel and highly effective technology

OBJECTIVES

A new device for percutaneous nephrolithotomy, combining Lithoclast (LC) and ultrasound (US) lithotripsy, was developed. Under standardized in vitro conditions, we evaluated the efficacy of the new technique using artificial stones. Combined application of pneumatic and US lithotripsy was compared with each of the two components alone.

METHODS

Five different artificial stones of defined hardness were used. Disintegration was performed under defined pressure in a water bath. The time until the first fragmentation and until complete disintegration to fragments of 2 mm or smaller was measured for LC and US alone and for combined lithotripsy. Furthermore, the disintegrated partition after 1 minute and time until 50% disintegration of each stone was determined.

RESULTS

With regard to first fragmentation and complete disintegration, LC and US combination showed superior efficacy. First fragmentation was achieved 25 to 200 times faster and complete disintegration in a range of 11 to 15 minutes. No complete disintegration was possible by LC and US alone within a time limit of 20 minutes. The disintegrated stone mass after 1 minute was 1.5 to 4 times larger in combined lithotripsy and the 50% disintegration time was 30% to 50% compared with LC or US alone. No technical defects occurred.

CONCLUSIONS

Combining LC and US in one device for percutaneous nephrolithotomy shows promising in vitro results in an artificial stone model. It seems to provide superior efficacy in the disintegration parameters important for clinical practice.

Experimental studies and first clinical experience with a new Lithoclast and ultrasound combination for lithotripsy

OBJECTIVES

A new lithotriptor for intracorporeal lithotripsy was developed combining the two most effective lithotriptors. A combination of the mechanically driven Lithoclast Master and a new ultrasonic device was constructed. Efficacy was tested in standardized model stones and in patient treatment.

MATERIAL

The new lithotriptor is composed of a Lithoclast Master and an ultrasonic device (EMS, Nyon, Switzerland). The 1.0 mm Lithoclast probe is advanced off-center through the hollow 3.3 mm ultrasonic probe and protrudes about 1 mm. Five different artificial stones of defined hardness and density were used as model stones for disintegration. Time until first fragmentation and complete fragmentation (particles smaller than 2.2 mm to fit through the ultrasonic probe), percent disintegration after 1 min and time until 50% disintegration were determined for the new device as well as lithoclast and ultrasound alone. A total of 68 patients were treated by percutaneous nephrolitholapaxy (PNL) with the new device from February 1999 to August 2001. Lithotripsy was performed after fluoroscopically guided puncture of the lower calix and dilatation of the nephrostomy tract with coaxial bougies. Thirty-five patients had complete and 33 patients partial staghorn calculi.

RESULTS

First fragmentation was reached 25-200 times faster with the combination as with either mode alone. Disintegrated stone mass after 1 min was 1.5-4 times larger in combined lithotripsy and 50% disintegration time 30-50% shorter. Clinically, complete stone free rate (KUB and ultrasound) was 66% after the first PNL. Sixteen out of 68 patients had a second look PNL with an overall stone free rate of 89.7% by dismission. Stone composition was calcium-oxalate-monohydrate in 13%, Ca-ox-monohydrate/uric acid in 35%, apatite in 20% and cystine in 11%.

CONCLUSION

In in vitro experiments and clinically the new lithotriptor provides easy handling and high effectivity in fragmentation of all stones regardless of their composition.

A new type of artificial urinary calculi: in vitro study by spiral CT

RATIONALE AND OBJECTIVES

Artificial urinary calculi similar to natural stones have long been sought in urologic research. In an experimental study, the authors assessed the CT characteristics of a new type of artificially produced urinary calculus [BON(N)-STONE].

METHODS

Six different types of urinary calculi (uric acid, struvite, cystine, calcium oxalate, brushite, and apatite) were produced by a coating technique in which several layers of a suspension of pure substance were applied around a core and dried. A total of 60 stones (10 per group) were studied by spiral CT at two energy levels (100 and 120 kV, 250 mA) with 1-mm slice thickness.

RESULTS

All calculi showed a small hyperdense core surrounded by a homogeneous matrix and a slightly hyperdense outer rim. From the least to the most dense, the stone types were uric acid, struvite, cystine, calcium oxalate, brushite, and apatite. Absolute CT values at 100 and 120 kV could differentiate between all groups of stones at a significance level of P < 0.001 or better. Attenuation values were in a comparable range to reported values for natural stones, with the exception of uric acid and struvite, which were notably lower.

CONCLUSION

These artificially produced urinary calculi showed properties similar to those of natural stones. Thus, this seems to be a promising stone model for further investigations.