VIRTUAL BIOPSY BY MEANS OF MINIATURIZED FIBER OPTICS ULTRASONIC TRANSDUCERS

摘要

Most advanced ultrasonic diagnostic systems, both for Non Destructive Testing and for clinical applications, are based on spectral analysis of ultrasonic signals (Watson et al., 2000). The diagnostic power of these systems strongly depends on the available ultrasonic bandwidth for differentiating media, due to their frequency selective attenuation. In addition, recent developments in ultrasonic biomedical applications, especially for intravascular and intraluminal echography, have led to significant demand for simple and miniaturized devices having good efficiency, in order to allocate the transducer in extremely small and low-cost catheters. Unfortunately, the present generation of transducer for clinical echography adopts piezoelectric ceramics (Foster, 2000), which exhibit a typical spectrum centered on a resonance frequency; the widening of the spectrum is obtained to the detriment of efficiency, by mechanically damping the oscillations. Moreover, these devices need cumbersome electrical wiring for excitation and signal readout. Recent progresses in optoacoustics let us foresee the possibility to realize complete miniaturized transmitting-receiving transducers able to generate and detect wide-band high-frequency ultrasounds by laser light. Thermoelastic ultrasound generation is an intrinsically wide-band technique and, under proper conditions, flat-band ultrasonic signals can be produced (Schruby and Drain, 1990). The case in which the light is arried by a fiber and the laser target is constituted by a thin absorbing film is of special interest for medical application; it has been widely studied by our group (Biagi et al., 2001), and the results are reviewed in Section 2.1. Many works presented in literature (Beard et al., 2000; Hamilton et al., 2000) indicate the way in which a fiber-based optoacoustic interferometric receiver can be realized. Several experiments carried out by us confirm this fact and the results are reported in Section 2.2.