Fig. 1 (above). X-ray image of a stone (and gas) before (top picture) and after (bottom picture) lithotripsy treatment.

It would be very useful to have a continuous monitor of whether the stone is breaking up. If too few shocks are given, the stone is not broken up, and the patient has to return for re-treatment, with commensurate costs in terms of waiting- and theatre-times,

patient discomfort, staff costs etc. Conversely if more shocks are given than is required to break up the stone, there is unnecessary tissue exposure to the shock wave, and the limited lifetime of the expensive lithotripter shock wave source is unnecessarily used up.

Continuous monitoring by X-rays is not possible because of exposure issues. Therefore this project sought to develop a passive sensor which sits on the patient's body and simply listens to what is happening. This sensor sends no signal into the body and so there are no 'dosage' issues associated with it, the way there are with X-ray sensors: it simply listens and interprets the sounds, a sort-of 'smart stethoscope'.

As these pages will show, not only is it possible to diagnose stone fracture in this way, but the sensor can also indicate whether the lithotripter focus stays on-target (it can for example move if the patient does, exposing healthy tissue to the powerful shock wave).

How does it work?  Immediately after the shock wave is sent into the body, sound echoes around within the torso. These pages describes a project which uses those echoes to determine whether the lithotripsy treatment has been successful in breaking up the stone.

The work was collaboration between the University of Southampton, Precision Acoustics Ltd. and Guys and St. Thomas' Health Trust, with useful discussion with the National Physical Laboratory.

Together they designed, built the listening device, which was then tested a both in the laboratory and the clinic. Two routes for interpreting its output were following. First, the sounds of successful, unsuccessful and indeterminate (a non-acoustic judgment by the surgeon from X-rays and follow-up) treatments were played to surgeons, so that they could empirically gain a sense of what acoustic record corresponds to a given clinical outcome. Second, a computation fluid dynamics (Fig.4) were used to simulate the production of these sounds, so that we could objectively interpret the output of the listening device.

Click on the links below for details.

Non-technical Introduction

2. Introduction to lithotripsy (Tutorial)

3. Formal report on the project

4. Hear for yourself the sounds, and see whether you can distinguish a successful treatment

5. Publications

Press and media reports

Fig. 2 (above). Photograph of a the sensor prior to its placement on the patient's skin.

Fig. 3 (above). Photograph of a the sensor taped in place on the patient's skin.

Fig. 4 (above) This animation (by student AR Jamaluddin) has rotational symmetry about the axis shown by the black horizontal line in the figure. It shows a region of water 1.2 mm long, in which sites a spherical air bubbles of radius 60 microns. A lithotripter shock wave is incident from the left. It causes the bubble to collapse and involute, such that the 'upstream' bubble wall forms a liquid jet that passes through the middle of the bubble. When this impacts the 'downstream' bubble wall, a blast wave is produced. Details of the Computational Fluid Dynamics can be found here. High speed photography of a similar laser-induced bubble jetting event can be found by clicking here.

Principal Investigator: TG Leighton    Co-investigators: GJ Ball, AJ Coleman

Collaboration: PR White, A Hurrell

Students: AR Jamaluddin, F Fedele

Sponsored by the EPSRC (GR/N19243/01)