Transmitted ultrasound for relief of obstruction in ureters and arteries: Current status

Abstract

In 1970, we embarged on a project to use ultrasonic energy for the recanalization of blocked arteries. This study was prompted by a suggestion by a patient with severe coronary artery disease, who is a member of the Department of Electrical Engineering. At that time we were aware that efforts had been made to use ultrasonic energy for therapeutic purposes, and have since become awrare of others. For example, Dotter (1) and others had attempted recanalization of femoral arteries using simple mechanical methods of dilatation with catheters of increasing size; such procedures had achieved limited success in the alleviation of gangrene of the foot.Our initial efforts were directed toward designed and constructing an apparatus t o transmit ultrasonic energy t o the tip of a flexible line which could be passed through a catheter. We rejected the concept of placing the transducer within the body -i.e., at the tip of the linebecause of the difficulties of ensuring adequate insulation at potentially lethal voltages. Accordingly, our efforts were concentrated on the design of an external transduction system. Because there was a considerable reservoir of information on ultrasonic transducers, our main problem was therefore the development of an efficient transmission system with optimal impedance matching.* The requirements to be met were: selection of the best materials, minimizing heat production, and preventing mechanical failure of the line or its connections. High strength aircraft aluminum (7075-T6) was selected for the quarter-wave matching stubs and concentrating cone (Fig. 1, 1 and 2). The transducers, of lead-zirconium titanate , are located at a stress maximum between the quarter-wave matching stubs and are pre-stressed by an aluminum collar to -30 tons/sq. in. ( 4 x l o 9 dynes/sq. cm).Electrical contact between the silvered faces of the t,wo transducers is made by means of a brass disc (solid in Figure 1, l ) , and the two quarter-wave matching stubs are symmetrical about this. The concentrating cone (Fig. 1, 2) is catenoidal in design and one-half wavelength in length at 25 kHz. Thus each quarter-wave matching stub is about 2 ins. long and the cone 4 ins. Design equations for matching stubs and cone are well-known (2), and are of the following general form :where p = density of material used R = radius at any given point z = longitudinal displacement variable x = independent displacement variable E = Young's modulus Boundary conditions are zero stress at one termination of the quarter stubs and at both ends of the cone.The above equation governs dispersive propagation in the stubs and cone. For non-dispersive propagation in the transmission line (Fig. 1, 3), equation (1) yields X' L = p w h e r e A= wavelength and % = frequency.Cobalt nickel alloy (Elgiloy) was selected for the transmission line because of its excellent P VOLUME 2, NUMBER 3 217

Ultrasonic fragmentation of large risidual Biliary tract stone

“…On February 9, 1977 the stone was looped in a 50 mm basket through the T-tube tract. The ultrasonic drill (8) was passed through the hollow core of the basket. Under fluoroscopic control, the stone was drilled (Fig.…”