Biomedical subjects

Achim M Loske

Publications and source records attributed to Achim M Loske.

8 recordsLinked to original sources

PubMed2005

[Increased fragmentation efficiency by enhancement of cavitation for extracorporal shock wave lithotripsy].

The non-invasive disintegration of kidney stones using shock waves, referred to as extracorporal shock wave lithotripsy, has been successful for more than twenty years in treating patients having renal and ureteral stones. Two modified shock wave generators are described in this article. The novel systems produce two similar shock waves (tandem shock waves) generated with a short time delay. The second shock wave arrives during collapse of the bubbles generated in the neighborhood of the stone due to the first shock wave. This may increase cavitation bubble collapse and could enhance cavitation-induced damage to kidney stones during shock wave lithotripsy. In vitro comparison of standard systems with the new designs showed that fragmentation efficiency of artificial kidney stones was significantly enhanced using tandem shock waves.

Humans↗

PubMed2005

Dual pulse shock wave lithotripsy: in vitro and in vivo study.

PURPOSE: We evaluated the performance of a novel dual pulse lithotriptor for extracorporeal lithotripsy. MATERIALS AND METHODS: A piezoelectric lithotriptor was modified to produce pairs of successive (tandem) shock waves. Four kidney stone models were exposed in vitro to 500 single shock waves with a standard lithotriptor. Another set of stones was exposed 1 at a time to 250 pairs of shock waves with the tandem lithotriptor. The time delay between the first and second shock waves was increased in steps of 50 microseconds between 100 and 600 microseconds. Four stones were used per delay, ie 44 phantoms were fractured with the tandem system. Rabbits were used in vivo to demonstrate that the novel device does not produce more tissue trauma. Five rabbits were exposed to shock waves generated by the new device, 5 were treated with the standard system and 5 served as the sham treated group. Renal damage caused by the 2 systems was compared 1 week after shock wave application. RESULTS: Enhanced fragmentation efficiency was achieved at a delay of 250 microseconds. In vivo results indicate that the dual pulse shock wave generator does not produce more kidney tissue damage. CONCLUSIONS: Tandem lithotriptors may improve the quality and rate of stone comminution without increasing tissue damage. The device enhances cavitation induced damage to kidney stones. Extensive in vivo experiments will be important to evaluate the new design.

Animals↗

PubMed2004

Evaluation of a bifocal reflector on a clinical lithotripter.

PURPOSE: To perform in vitro and in vivo tests using a clinical lithotripter in order to determine whether a bifocal reflector is more efficient and produces the same or less tissue damage than a conventional ellipsoidal reflector for electrohydraulic lithotripters. MATERIALS AND METHODS: A standard ellipsoidal and a novel bifocal reflector were tested on a Tripter Compact lithotripter (Direx Medical Systems, Petach Tikva, Israel). The bifocal reflector was constructed by joining two sectors of two rotationally symmetrical ellipsoidal reflectors having different distances between their foci. The F1 foci of the sectors coincided, creating a separation between the F2 foci. The fragmentation efficiency of the reflectors was compared using kidney-stone models. Shockwave-induced trauma was evaluated in vivo by treating both kidneys of six healthy dogs. One kidney was exposed to shockwaves generated with the conventional reflector, and the other kidney was treated using the bifocal reflector. Pressure measurements were obtained for both reflectors using needle hydrophones. RESULTS: The new design appeared to be more efficient than the conventional reflector in breaking up kidney-stone models. Tissue damage did not increase when using the bifocal reflector. CONCLUSION: The use of bifocal, instead of standard ellipsoidal, reflectors should be considered as an alternative to improve extracorporeal shockwave lithotripsy.

Animals↗

PubMed2004

Out-of-focus shockwaves: a new tissue-protecting therapy?

INTRODUCTION: It seems that vasoconstriction induced by 12 Kv shock waves reduces kidney lesions caused by subsequent application of 24 Kv shock waves. The lowest shock wave voltage to induce this protective effect is not known yet and may be lower than the common energy setting of commercial lithotripters. Because of this we propose the application of shock waves as a tissue protecting method. MATERIALS AND METHODS: Preliminary pressure measurements were performed on an experimental unmodified HM3 lithotripter (at 12 and 24 Kv), using a 20 ns rise time needle hydrophone connected to a 100 MHz digital oscilloscope. Ten pressure records were obtained at different aging of the spark plug. A new spark plug was used for each voltage. Pressure measurement were also performed on a Tripter compact lithotripter at 6 positions along the focal axis, starting at F2 and moving away from the reflector, using maximum voltage and capacitance (22 Kv, HI-2). The position on the focal axis of the Tripter Compact with the same pressure as measured at 12 Kv on the HM3 at F2 was chosen as the prophylactic treatment spot (PTS). In vivo pressure measurement were done on the Tripter Compact placing the needle hydrophone inside the lower pole of the right kidney of an anesthetized healthy 25 kg female pig. Measurements were done at the same positions mentioned above, without moving the hydrophone, inside the pig. For both in vitro and in vivo measurements, the radiopaque hydrophone was aligned with the focal axis, using the fluoroscopy system of the lithotripter. RESULTS: The mean positive pressure peak at the second focus of the HM3 lithotripter was 64 and 153 mV at 12 Kv, respectively. Coefficients of variations were 0.28 and 0.13. No significant pressure differences were detected below 700 and 2220 discharges with the HM3 and the Tripter compact, respectively. The difference peak amplitudes are all significant (p<0.01 in a one tailed test) with the exception of F2 and F2+1 Ohm. CONCLUSIONS: Prophylactic administrations of out-of-focus shock waves may reduce tissue damage during SWL. Experiments in vivo are underway in order to prove this hypothesis.

Animals↗

PubMed2003

Conversion of an HM3 lithotripter into a research device.

PURPOSE: To describe the conversion of a Dornier HM3 lithotripter into a research device and evaluate its performance. MATERIALS AND METHODS: A used HM3 lithotripter was donated to our university by the St. Thomas' Hospital in London. It was disassembled, shipped to our laboratory, partially assembled, and modified as a research lithotripter. Pressure measurements at several positions and kidney stone model fragmentation tests were performed to evaluate the modified system. Results were compared with information published by other authors and data obtained in our laboratory using another electrohydraulic research lithotripter. RESULTS: Pressure records showed typical lithotripter waveforms with a rapid rise to about 50 MPa, followed by decay to a negative peak of approximately 9 MPa. Maximum compressional peaks were obtained at F2 and 25 mm below F2. Kidney stone model fragmentation was typical for electrohydraulic shockwave lithotripters. CONCLUSIONS: Comparison of pressure measurements with data obtained by other authors on the same lithotripter several years ago indicate that the pressure waveform has not changed significantly. A much smaller water tank, a small X-Y-Z positioner, and no X-ray imaging system facilitate the use of this shockwave generator for in vitro experiments with small samples such as vials containing cell suspensions, having the advantage of a reliable, well-known, and well-characterized commercial shockwave generator.

Biomedical Research↗

PubMed2002

Tandem shock wave cavitation enhancement for extracorporeal lithotripsy.

Extracorporeal shock wave lithotripsy (ESWL) has been successful for more than twenty years in treating patients with kidney stones. Hundreds of underwater shock waves are generated outside the patient's body and focused on the kidney stone. Stones fracture mainly due to spalling, cavitation and layer separation. Cavitation bubbles are produced in the vicinity of the stone by the tensile phase of each shock wave. Bubbles expand, stabilize and finally collapse violently, creating stone-damaging secondary shock waves and microjets. Bubble collapse can be intensified by sending a second shock wave a few hundred microseconds after the first. A novel method of generating two piezoelectrically generated shock waves with an adjustable time delay between 50 and 950 micros is described and tested. The objective is to enhance cavitation-induced damage to kidney stones during ESWL in order to reduce treatment time. In vitro kidney stone model fragmentation efficiency and pressure measurements were compared with those for a standard ESWL system. Results indicate that fragmentation efficiency was significantly enhanced at a shock wave delay of about 400 and 250 micros using rectangular and spherical stone phantoms, respectively. The system presented here could be installed in clinical devices at relatively low cost, without the need for a second shock wave generator.

Equipment Design↗

PubMed2002

Pressure-release versus rigid reflector for extracorporeal shockwave lithotripsy.

PURPOSE: To evaluate the advantages and disadvantages of using a pressure-release reflector instead of a rigid reflector to concentrate shockwaves for extracorporeal shockwave lithotripsy (SWL). MATERIALS AND METHODS: As in all electrohydraulic lithotripters, shockwaves were generated by electrical breakdown of water between two electrodes, located at the focus (F1) closest to a paraellipsoidal reflector. A pressure-release reflector, made out of polyurethane foam, was constructed and tested on a research lithotripter using kidney stone models. Fragmentation data and pressure measurements were compared with those of a conventional rigid reflector tested on the same device. RESULTS: The weight of stone model fragments remaining after shockwave exposure was less with the pressure-release reflector after screening through a 3.0 x 3.0-mm mesh. The residual fragment weight was less with the rigid reflector using 1.0 x 1.0- and 0.6 x 0.6-mm meshes. CONCLUSION: Pressure-release reflectors may maintain acceptable stone fragmentation while offering improved patient safety and should be considered for SWL.

Equipment Design↗

PubMedDate not supplied

CT attenuation value and shockwave fragmentation.

PURPOSE: To evaluate whether, in principle, the mean CT attenuation values of kidney stones could predict fragmentation by shockwaves. MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were tested. Artificial stones were weighed and exposed to 700 shockwaves at 21 kV at the focus of an electrohydraulic lithotripter. Fragments were strained through meshes with 2x2-mm and 3.1x3.1-mm openings. The material left on the meshes after shockwave exposure was dried and weighed on a precision scale. Half of all artificial stones were saturated by immersing them in water several days before fragmentation. Fragmentation coefficients (i.e., percent weight loss) were associated with CT attenuation values using a statistical model. RESULTS: Higher CT numbers resulted in lower fragmentation coefficients. Artificial stone weight was inversely proportional to the percent weight loss. Larger fragments were obtained at lower fragmentation coefficients. Statistical analysis revealed that fragmentation can be predicted knowing the weight and the CT number of a stone before shockwave application. CONCLUSION: Prediction of the number of shockwaves necessary for successful SWL could be possible. Our statistical model proved to fit in vitro fragmentation of artificial stones; however, clinical application requires further research.

Humans↗