ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aPA2. A review of current research on optical techniques for acoustic measurements in lithotripsy.

Andrew J. Coleman

Medical Phys. Directorate, Guy's and St. Thomas' Hospital Trust, London SE1 7EH, UK

Peter C. M. Galloway

Natl. Physical Lab., Teddington, Middlesex TW11 OLW, UK

This paper reviews some recent research on optical techniques for acoustic pressure measurement along with initial results obtained in the field of a newly developed electromagnetic-type shock wave source. A long-path-difference Michelson interferometer enables direct determination of the Doppler shift from a target to evaluate particle velocity in water in the range 1--100 ms[sup -1]. The instrument operates as a high-resolution spectroscope with a 532-nm wavelength laser source and a remote optical-head utilizing fiber links. The aim is to establish measurement standards in lithotripsy where conventional hydrophone-based procedures are inadequate. A second optical fiber ultrasound sensor, orginally developed for the measurement of photoacoustic transients in tissue, is also described [P. C. Beard and T. N. Mills, Proc. SPIE 2388, 446--457 (1995)]. This sensor employs a Fabry--Perot interferometer comprising a 50-(mu)m polymer film acoustically matched to water which is illuminated with light emerging from the fiber. An electromagnetic shock wave source developed recently by the Medical Physics Directorate (Guy's and St. Thomas' Hospital, London) has been used to compare measurements from the two interferometer systems with conventional hydrophone measurements.