High frequency nonlinear scattering and imaging of a submicron contrast agent

We investigate high frequency nonlinear scattering and imaging of a contrast agent comprised of submicron bubbles. Agent characterization experiments conducted at 20 and 30 MHz transmit frequencies with a broadband PVDF transducer confirm the production of substantial amounts of energy in the subharmonic and second harmonic regions. Nonlinear contrast imaging with intravascular ultrasound (IVUS) is then explored with a prototype mechanically scanned system. Pulse-inversion techniques were employed with a 20 MHz transmit frequency (F20) for second harmonic imaging (H40), and with a 40 MHz transmit frequency (F40) for subharmonic imaging (SH20). H40 was found to produce improvements in contrast-to-tissue signal ratios (CTR) for low transmit amplitudes (<0.3 MPa). SH20 was demonstrated at a range of pressures (0.2 to 2.2 MPa). These results show the feasibility of using a submicron agent for high frequency (>15 MHz) nonlinear contrast imaging and suggest the potential application of these techniques in IVUS.