Miniaturized fiber-optic ultrasound probes for endoscopic tissue analysis by micro-opto-mechanical technology

Abstract

A new Micro-Opto-Mechanical System (MOMS) technology for the fabrication of optoacoustic probes on optical fiber is presented. The technology is based on the thermoelastic emission of ultrasonic waves from patterned carbon films for generation and on extrinsic polymer Fabry-Perot acousto-optical transducers for detection, both fabricated on miniaturized single-crystal silicon frames used to mount the ultrasonic transducers on the tip of an optical fiber. Thanks to the fabrication process adopted, high miniaturization levels are reached in the MOMS devices, demonstrating fiber-optic emitters and detectors with minimum diameter around 350 and 250 μm respectively. A thorough functional testing of the ultrasound emitters mounted on 200 and 600 μm diameter optical fibers is presented, in which the fiber-optic emitter with a diameter of 200 μm shows generated acoustic pressures with peak-to-peak value up to 2.8 MPa with rather flat emission spectra extended beyond 150 MHz. The possibility to use the presented optoacoustic sources in conjunction with the fiber-optic acousto-optical detectors within a minimally invasive probe is also demonstrated by successfully measuring the ultrasonic echo reflected from a rigid surface immersed in water with various concentration of scatterers. The resulting spectra highlight the possibility to discriminate the effects due to frequency selective attenuation in a very wide range of frequencies within a biological medium using the presented fiber-optic probes.

Carbon‐Nanotube–PDMS Composite Coatings on Optical Fibers for All‐Optical Ultrasound Imaging

“…The ultrasound bandwidths achieved in this study were larger than most previously obtained with PDMS–carbon composites, which is important for achieving high spatial resolution. One exception can be found in the study of Vannacci et al, which yielded bandwidths beyond 150 MHz using coatings on optical fibers; however, the authors raised concerns about the degradation of their coatings with time . For the bilayer coatings in this study, improvements in bandwidth could be likely achieved by minimizing the thickness of the excess PDMS layer that overlies the composite.…”

Optical fiber ultrasound transmitter with electrospun carbon nanotube-polymer composite

“…A variety of methods have been reported for optical ultrasound transmitter fabrication. These include techniques such as dip-coating, 2,4 spin-coating, 15 chemical vapor deposition, 11,14,16 metal evaporation, 6 and etching 12,17 . Dip-coated and spin-coated absorber-elastomer composites on glass substrates have been implemented for fabrication of carbonaceous optical ultrasound generating surfaces 1,2,16 .…”

Laser generated ultrasound sources using carbon-polymer nanocomposites for high frequency metrology

“…Photoacoustics in this context is therefore often referred to as Laser Generated Ultrasound (LGUS). The key findings from the literature review of LGUS sources, including pressure amplitudes and bandwidths obtained, are briefly summarized in Table I. LGUS sources were either nanocomposites made of carbon nanoparticles and polymeric materials [30][31][32][33][34][35][36][37][38][39][40][41][42] or fabricated gold nanoparticle arrays and films. [43][44][45][46][47] Carbon nanoparticles such as multi-walled carbon nanotubes, candle soot nanoparticles, carbon nanofibers, carbon black and reduced graphene oxide or gold nanoparticles, were used as light absorbers.…”