Friedrich Ueberle

Extracorporeal shock waves act by shock wave-gas bubble interaction

The effect of extracorporeal shock waves on hemoglobin release from red blood cells was recently found to be minimized under minute static excess pressure. It was proposed that this can be explained by shock wave-gas bubble interaction. We substantiated this further by two experiments by applying shock waves to suspended human RBC in a lithotripter at a lower frequency (1 pulse every 5 s) and by administering just a single or 2 strong shock waves at 30 kV. Compared to the usual application rate of 1 discharge per s, the lower frequency reduced the hemoglobin release under minimal static excess pressure in the range from 0-100 kPa. A single strong shock wave released a small amount of hemoglobin at ambient pressure and a similar amount at 200 kPa excess pressure. Two strong shock waves increased the hemoglobin release considerably at ambient pressure when there was a 1- or a 10-s pause between them. Under 200 kPa excess pressure, the hemoglobin release was minimal. A similar low hemoglobin release was also found with 1 shock at ambient and the other at excess pressure. The results are interpreted as clear evidence of shock wave-gas bubble interaction as a dominant mechanism of shock wave action.

Destruction of gallstones and model stones by extracorporeal shock waves

The disintegration effectivity of an electrohydraulic lithotripter was evaluated by determining the acoustic energy that had to be applied, until all fragments of three artificial materials and human gallstones were cleared from a basket of 2.8 mm mesh size. The lithotripter had either an open ellipsoid, or the ellipsoidal axis was covered with a metal cage as used in clinical lithotripters to house the ultrasound scanner. Fragmentation was assessed at a low, medium and high voltage setting using 9 and 16 mm breeze block marbles, considered to be primarily fragmented by a cavitation-mediated mechanism; 16 mm glass marbles, considered to be primarily fragmented by a direct shock wave effect; 12 and 15 mm plaster balls as commonly used to monitor lithotripter output; and gallstones with a mean diameter of 16 mm. As a result, the acoustic energy for the disintegration of 9 and 16 mm breeze block marbles was 620 and 670 mJ cm-3, of glass marbles 3369 mJ cm-3, of 12 and 15 mm plaster balls 1599 and 1764 mJ cm-3 and of gallstones 8050 mJ cm-3. It was largely independent of pulse energy, specimen size and configuration of the shock wave source. It is concluded that acoustic energy is a major determinant of disintegration, independent of the presumed mechanism of destruction.

Impaired tensile strength after shock-wave application in an animal model of tendon calcification

Extracorporeal shock-wave application facilitates dissolution of rotator cuff calcifications. Therefore, disappearance or disintegration of tendon calcifications by shock waves might be appropriate for any kind of tendon calcification. Here, shock waves with various energy flux densities were applied to the mineralized medial gastrocnemius tendon of turkeys as an animal model. After application of shock waves in vivo, with energy flux density of 0.6 mJ/mm(2), histologic examination and microradiography did not show dissolution or disintegration of tendon calcifications. After shock-wave application in vitro, even for energy flux density of 1.2 mJ/mm(2) neither dissolution nor disintegration of tendon calcifications were observed. Biomechanical testing revealed significant impairment of tensile strength following shock-wave application in vitro, with energy flux density of 1.2 mJ/mm(2), but not with 0.6 mJ/mm(2). These results are important for considerations of clinical extracorporeal shock-wave application on tendon calcifications, as well as on tendon ossifications.

Acoustic energy determines haemoglobin release from erythrocytes by extracorporeal shock waves in vitro

Haemoglobin release from erythrocytes by extracorporeal shock waves from an electrohydraulic lithotripter was quantified and correlated with the acoustic energy administered to the cell container. Cells were exposed in 2-, 5.9-, and 10.5-mL vials to 100 shock waves delivered at a low, medium and high lithotripter output setting, both with and without covering of the central ellipsoidal axis by a metal cage. Using the identical set-up, previous experiments had shown that the fragmentation efficiency was linearly correlated with the delivered acoustic energy. As a result, shock waves generated from 0.83 microgram mJ-1 (in 2-mL vials) to 1.53 micrograms mJ-1 (in 10.5-mL vials) haemoglobin. At all vial types, the amount of haemoglobin correlated linearly with the delivered acoustic energy (r = 0.96 in 2-mL, r = 0.97 in 5.9-mL and r = 0.98 in 10.5-mL vials). It was independent of the presence of the cage.

Ballistic Pain Therapy Devices: Measurement of Pressure Pulse Parameters

Ballistic pressure pulse sources are used for the treatment of soft tissue pain. The devices use a technical principle, which is known from air guns, i.e. a projectile is accelerated by pressurized air towards a metal plate (applicator). At the patient side, a fast (4..5μs), almost singular pressure pulse of 2..10 MPa is created, which is followed by an equally short rarefaction phase of about the same amplitude. In order to characterize the pressure pulse devices, a “dry” test bench was built mimicking the properties of the patient skin by a silicone layer. Comparison of measurements in water and with the silicone layer demonstrated, that the pressure pulses could be reproduced almost identical in both situations. At present, 4 different hand pieces were evaluated using the “dry” test bench. The behaviour of the hand pieces when the pulse repeat rate was changed from single pulse to maximum rate (20..21 per second) was assessed. It turned out, that the pulse amplitudes and intensities depend strongly on the type of hand piece, and on the driving pressure. A decrease of peak pressure down to 63% was found at a pulse rate of 20 Hz as compared to single pulse amplitude at the same driving pressure. Further measurements show, that a strongly damped, low amplitude inertial oscillation of ca. 10 ms period follows after each pressure pulse.

Anwendung von Stosswellen für den Transfer von Molekülen in Zellen

A mixture of human iymphocytes (LJ210) and fhiore\cent marker molecules are sitbjected to shockwaves in vitro. Due to the transient cavitation generated by the shockwaves, the cells take up the marker molecules. Cavitation /.v characterized by the bubble collapse times. An electrohydraulic generator XL-1 und a piezoelectric generator PR-ll were used; PR-ll was more effective. Depending on the pulse energy and number ofpulses, up to 70% of the surviving cells took up the molecules. Shockwave-mediated molecule transferprovides a useful tool for the transfer of molecules into cells, which can be used äs a research tool in the medical and biotechnological fields. Due to the large penetration potential of shockwaves into the body. the method may befurther developed for in vivo transfer ofdrugs and cell transfection use. Keywords— shockwave. cavitation, cell, molecule transfer, biotechnology

Cardiac MR: Imaging of the Foetal Heart Dynamics using Doppler Ultrasound Triggering

Magnetic Resonance Imaging (MRI) could be of high importance for imaging the foetal heart, especially to diagnose anomalies of the heart and the great vessels. While in the imaging of adult hearts MR triggering can be done through Electro-Cardiogram (ECG) or finger pulse oximetry (POX), these methods cannot apply because the foetus lies within the uterus. The aim of this project was to demonstrate the feasibility of non-invasive triggering of the MR by the foetal heart beat using Doppler Ultrasound. An artefact-free Doppler transducer was used to pick up the heart motion signals. An algorithm was developed which allowed triggering of the MR system. In an animal study, successful imaging of the foetal sheep heart was performed on 9 pregnant ewes at a 1.5T scanner. With dedicated software, MR cine sequences of the foetal heart beat and standard twoand four chamber images of the structures of the hearts of 124 days old foetuses could be recorded with a good resolution.

Characterization of Unfocused / Weakly Focused Pressure Pulse Sources for Extracorporeal Pain Therapy ("Radial Shock Wave Therapy" Sources).

Extracorporeal “Shock Wave” Therapy (ESWT) is widely and successfully used for the treatment of orthopedic pain situations. Based on measurements of different pressure pulse devices, a set of parameters for the characterization of unfocused / weakly focused pressure pulse sources is proposed, which may be used to initiate an internationally harmonized (IEC) standard for the measurement and characterization of these devices and to further develop an appropriate safety standard.

Field mapping of ballistic pressure pulse sources

Abstract Ballistic pressure pulse sources are used since late 1990s for the extracorporeal treatment of chronic Enthesitis. Newly indications are found in trigger-point-therapy for the treatment of musculoskeletal disorders. In both applications excellent results without relevant side effects were found in clinical trials. The technical principle of pressure pulse source is based on the same techniques used in air guns. A projectile is accelerated by pressurized air and hits the applicator with high kinetic energy. By this a compression wave travels through the material and induces a fast (4..5μs), almost singular pressure pulse of 2..10 MPa, which is followed by an equally short rarefaction phase of about the same amplitude. It is assumed that the pressure pulse accounts for the biomedical effects of the device. The slower inertial motion of the waveguide is damped by elastic stoppers, but still can be measured several micro seconds after the initial pressure pulse. In order to characterize the pressure pulse devices, field mapping is performed on several radial pressure pulse sources using the fiber optic hydrophone and a polyvinylidenfluorid (PVDF) piezoelectric hydrophone. It could be shown that the current standard (IEC 61846) is not appropriate for characterization of ballistic pressure pulse sources.

Pressure Pulse Fields: Comparison of optical hydrophone measurements with FEM Simulations.

Several approaches for simulating ultrasound are available. The main tools are Finite or Boundary element methods and the spatial impulse response methods. Finite and Boundary Element methods are the most flexible but also the most computationally expensive tools available. On the other hand the spatial impulse response is restricted only to linear acoustic problem, but with low computational demands and prime costs. While with diagnostic ultrasound it’s mostly sufficient to confine the equations on linear acoustics, this simplification is not possible with therapeutic ultrasound. High pressure amplitudes of therapeutic ultrasound transducers create strong nonlinear effects in the medium, which cannot be simulated using linear acoustic theory. We compare two types of optical hydrophones developed for pressure pulse measurements, the fiber-optic-hydrophone and the light-spot-hydrophone. Both are based on reflection changes of a laser beam due to the medium density modulation by a sound wave at the sensitive end of the device. The aim of our work is to compare the measurement of a Panametrics NDT Transducer with simulations using ABAQUS FEM Software. FEM, Abaqus, LSHD, FASO, FOPH, Acoustic Simulation