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Background and Purpose-A recent study showed a dramatic increase in cerebral hemorrhage comprising atypical locations with low-frequency ultrasound-mediated recombinant tissue plasminogen activator-thrombolysis in humans. Here, we provide a possible explanation for this phenomenon by a side effect observed in a study using the similar ultrasound device. Methods-The study was originally undertaken to investigate by transcranial Doppler sonography, positron emission tomography and perfusion MRI whether transcranial application of wide-field low-frequency ultrasound (300 kHz) improves cerebral hemodynamics in patients with cerebral small vessel disease. Results-Showing no clear positive effect on cerebral hemodynamics in 4 patients and on cerebral perfusion (positron emission tomography) in 2 patients, the study has been terminated early because of a remarkable side effect in the first patient (a 62 year-old man) undergoing perfusion-MRI: detection of frontoparietal extravasation of Gadolinium contrast agent (applied during MRI perfusion imaging preinsonation) on MRI immediately postinsonation. Conclusions-Abnormal permeability of the human blood-brain barrier can be induced by wide-field low-frequency insonation.The observed excessive bleeding rate with low-frequency sonothrombolysis might thus be attributable to primary blood-brain barrier disruption by ultrasound. Key Words: blood-brain barrier Ⅲ hemodynamic phenomena Ⅲ leukoaraiosis Ⅲ side effect Ⅲ ultrasound A recent study showed a dramatic increase in cerebral hemorrhage with ultrasound-mediated recombinant tissue plasminogen activator (rtPA)-thrombolysis in humans using low-frequency ultrasound. 1 We provide a possible explanation for this phenomenon by a side effect observed in a lately performed study using the similar ultrasound device.In that study, we originally aimed to investigate whether transcranial application of low-frequency ultrasound improves cerebral perfusion and hemodynamics in chronically hypoperfused brains such as of patients with cerebral small vessel disease. The investigation was stimulated by animal data showing NO-mediated flow recovery in ischemic tissue by lowfrequency ultrasound. 2,3 MethodsFour men (aged 62 to 73 years) with severe cerebral small vessel disease were studied after approval by the local Ethics committee. Within different sessions, cerebral hemodynamics before and immediately after application of low-frequency ultrasound were to be assessed by transcranial Doppler (TCD) measurements in the middle cerebral artery (for details see Table), 15 O-H 2 O positron emission tomography (PET) studies, and MRI perfusion measurements (including application of Gadolinium-DTPA [Gd-DTPA] before and after insonation).Low-frequency ultrasound was applied through the right temporal bone window using an array transducer fixed by a headband. The insonation system (NeuroFlow, Walnut Technologies, Inc) was the same used in the sonothrombolysis study. 1 It consisted of an array transducer emitting low-frequency ultrasound (Ϸ300 kHz) with ...

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height. In the experiments grey cast iron (0.6025) was machined with typical high speed cutting parameters (v c = 450 m/min, f = 0,16 mm) without cooling lubricant supply. Figure 5 summarises the results for a prototype with a diameter of d = 10.6 mm. In comparison to experiments with standard cemented carbide drills the primary processing time could be reduced to 50±75 % depending on the recommended cutting parameters. In addition, a considerably better bore hole quality could be achieved. The surface roughness lies in a range of R z = 3±7 lm in contrast to R z = 6±14 lm in experiments with the cemented carbide drill. Similarly the diameter deviation could be kept in the IT 7 range (comp. exp.: DD = 0.018±0.05 mm) and the roundness deviation Dt lies between 0.0075 mm and 0.017 mm (comp. exp.: Dt = 0.01±0.035 mm). The cutting edge of the ceramic insert did not show any wear during the entire machining process.The tools finally failed spontaneously at the contact zone of ceramic and carbide exactly in the region for which the maximum residual stresses were computed. [5] Therefore, the shape of the contact zone must be optimised so that the residual load of the structure after the brazing process is reduced. In addition to the currently performed FE-analyses of the brazing process, the mechanical load during the machining process will be taken into account in future FE-simulations. Here especially the force distribution along the cutting edge should be considered appropriately in order to achieve valid results. [6,7] The ultrasonic welding technique is wide spread in industry. It is mainly used for joining polymers with polymers and metals with metals. [1±5] For several years ultrasonic weldings between different materials as metals with ceramics or metals with glasses were successfully performed at the Institute of Materials Science, University of Kaiserslautern. [6] Recent results show, that beside compact glass also fibre glass with or even without thermoplastic matrix can be welded to metals. In principle both ultrasonic plastic welding as well as ultrasonic metal welding can be used. [7] The significant difference between these welding techniques is the direction of the ultrasonic oscillation. It is perpendicular to the weld area in the plastic welding technique and parallel to the weld contact area in the metal welding technique. The investigations described in the paper were carried out using both kinds of welding techniques.Weldings between consolidated PA-12/E-glass composite material and AlMg3 sheet metals are described. Some test series were performed with an annealed foil of pure aluminium in between the composite and the metal (Fig. 1).